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PURPOSE Compared with people living without HIV (PWOH), people living with HIV (PWH) and cancer have traditionally been excluded from immune checkpoint inhibitor (ICI) trials. Furthermore, there is a paucity of real-world data on the use of ICIs in PWH and cancer. METHODS This retrospective study included PWH treated with anti–PD-1- or anti–PD-L1-based therapies for advanced cancers. Kaplan-Meier method was used to estimate overall survival (OS) and progression-free survival (PFS). Objective response rates (ORRs) were measured per RECIST 1.1 or other tumor-specific criteria, whenever feasible. Restricted mean survival time (RMST) was used to compare OS and PFS between matched PWH and PWOH with metastatic NSCLC (mNSCLC). RESULTS Among 390 PWH, median age was 58 years, 85% (n = 331) were males, 36% (n = 138) were Black; 70% (n = 274) received anti–PD-1/anti–PD-L1 monotherapy. Most common cancers were NSCLC (28%, n = 111), hepatocellular carcinoma ([HCC]; 11%, n = 44), and head and neck squamous cell carcinoma (HNSCC; 10%, n = 39). Seventy percent (152/216) had CD4+ T cell counts ≥200 cells/µL, and 94% (179/190) had HIV viral load CONCLUSION Among PWH, ICIs demonstrated differential activity across cancer types with no excess toxicity. Safety and activity of ICIs were similar between matched cohorts of PWH and PWOH with mNSCLC.

PURPOSE Currently, there are no robust biomarkers that predict immunotherapy outcomes in metastatic melanoma. We sought to build multivariable predictive models for response and survival to anti-programmed cell death protein 1 (anti–PD-1) monotherapy or in combination with anticytotoxic T-cell lymphocyte-4 (ipilimumab [IPI]; anti–PD-1 ± IPI) by including routine clinical data available at the point of treatment initiation. METHODS One thousand six hundred forty-four patients with metastatic melanoma treated with anti–PD-1 ± IPI at 16 centers from Australia, the United States, and Europe were included. Demographics, disease characteristics, and baseline blood parameters were analyzed. The end points of this study were objective response rate (ORR), progression-free survival (PFS), and overall survival (OS). The final predictive models for ORR, PFS, and OS were determined through penalized regression methodology (least absolute shrinkage and selection operator method) to select the most significant predictors for all three outcomes (discovery cohort, N = 633). Each model was validated internally and externally in two independent cohorts (validation-1 [N = 419] and validation-2 [N = 592]) and nomograms were created. RESULTS The final model for predicting ORR (area under the curve [AUC] = 0.71) in immunotherapy-treated patients included the following clinical parameters: Eastern Cooperative Oncology Group Performance Status, presence/absence of liver and lung metastases, serum lactate dehydrogenase, blood neutrophil-lymphocyte ratio, therapy (monotherapy/combination), and line of treatment. The final predictive models for PFS (AUC = 0.68) and OS (AUC = 0.77) included the same variables as those in the ORR model (except for presence/absence of lung metastases), and included presence/absence of brain metastases and blood hemoglobin. Nomogram calculators were developed from the clinical models to predict outcomes for patients with metastatic melanoma treated with anti–PD-1 ± IPI. CONCLUSION Newly developed combinations of routinely collected baseline clinical factors predict the response and survival outcomes of patients with metastatic melanoma treated with immunotherapy and may serve as valuable tools for clinical decision making.

The role of neoadjuvant therapy is undergoing an historic shift in oncology. The emergence of potent immunostimulatory anticancer agents has transformed neoadjuvant therapy from a useful tool in minimizing surgical morbidity to a life-saving treatment with curative promise, led by research in the field of melanoma. Health practitioners have witnessed remarkable improvements in melanoma survival outcomes over the past decade, beginning with checkpoint immunotherapies and BRAF-targeted therapies in the advanced setting that were successfully adopted into the postsurgical adjuvant setting for high-risk resectable disease. Despite substantial reductions in postsurgical recurrence, high-risk resectable melanoma has remained a life-altering and potentially fatal disease. In recent years, data from preclinical models and early-phase clinical trials have pointed to the potential for greater clinical efficacy when checkpoint inhibitors are administered in the neoadjuvant rather than adjuvant setting. Early feasibility studies showed impressive pathologic response rates to neoadjuvant immunotherapy, which were associated with recurrence-free survival rates of over 90%. Recently, the randomized phase II SWOG S1801 trial (ClinicalTrials.gov identifier: NCT03698019 ) reported a 42% reduction in 2-year event-free survival risk with neoadjuvant versus adjuvant pembrolizumab in resectable stage IIIB-D/IV melanoma (72% v 49%; hazard ratio, 0.58; P = .004), establishing neoadjuvant single-agent immunotherapy as a new standard of care. A randomized phase III trial of neoadjuvant immunotherapy in resectable stage IIIB-D melanoma, NADINA (ClinicalTrials.gov identifier: NCT04949113 ), is ongoing, as are feasibility studies in high-risk stage II disease. With a swathe of clinical, quality-of-life, and economic benefits, neoadjuvant immunotherapy has the potential to redefine the contemporary management of resectable tumors.

PURPOSE Improved understanding of the incidence, risk factors, and timing of CNS metastasis is needed to inform surveillance strategies for patients with melanoma. PATIENTS AND METHODS Clinical data were extracted from the databases of 2 major melanoma centers in the United States and Australia for 1,918 patients with American Joint Committee on Cancer (AJCC) 8th edition stage III melanoma, diagnosed from 1998-2014, who had (negative) baseline CNS imaging within 4 months of diagnosis. The cumulative incidence of CNS metastasis was calculated in the presence of the competing risk of death, from stage III presentation and at benchmark time points 1, 2, and 5 years postdiagnosis. RESULTS At a median follow-up of 70.2 months, distant recurrence occurred in 711 patients (37.1%). The first site of distant metastasis was CNS only for 3.9% of patients, CNS and extracranial (EC) for 1.8%, and EC only for 31.4%. Overall, 16.7% of patients were diagnosed with CNS metastasis during follow-up. The cumulative incidence of CNS metastasis was 3.6% (95% CI, 2.9% to 4.6%) at 1 year, 9.6% (95% CI, 8.3% to 11.0%) at 2 years, and 15.8% (95% CI, 14.1% to 17.6%) at 5 years. The risk of CNS metastasis was significantly influenced by patient sex, age, AJCC stage, primary tumor site, and primary tumor mitotic rate in multivariable and conditional analyses. High primary tumor mitotic rate was significantly associated with increased risk of CNS metastasis at diagnosis and all subsequent time points examined. CONCLUSION Similar rates of CNS metastasis were observed in 2 large, geographically distinct cohorts of patients with stage III melanoma. The results highlight the importance of primary tumor mitotic rate. Furthermore, they provide a framework for developing evidence-based surveillance strategies and evaluating the impact of contemporary adjuvant therapies on the risk of CNS metastasis development.

9558 Background: Adjuvant immunotherapy has revolutionized the management of resectable melanoma, substantially reducing the risk of recurrence but at the risk of immune-related adverse events (AE). This study aimed to quantify patients' preferences for adjuvant immunotherapy, the influence of varying levels of key attributes, and baseline characteristics associated with preferences. Methods: We performed a discrete choice experiment (DCE), including patients with resected stage III melanoma considering or having received adjuvant immunotherapy. Patients chose between twelve randomly presented choice tasks of two alternative options (adjuvant immunotherapy versus observation without adjuvant immunotherapy). The two options varied across two-three levels of six attributes: chance of 3-year melanoma recurrence, mild, permanent, or fatal AE, drug regimen, and out-of-pocket costs. We calculated the marginal rate of substitution (MRS, how much an individual was willing to trade one attribute for preferred levels of another) and willingness-to-pay (WTP, maximum price to trade their preferred attributes) per year. Results: One hundred and sixteen patients completed the DCE. Patients chose adjuvant immunotherapy over observation without adjuvant immunotherapy in 70% of choice tasks. Patients preferred adjuvant immunotherapy with reduced probabilities of recurrence (OR 0.76, 95% CI 0.70-0.83, p

TPS9599 Background: Anti-PD1-based immunotherapies have been approved for many cancer types and are now a standard therapy for advanced melanoma. Despite this, ̃50% of advanced melanoma patients (pts) fail to respond or eventually progress after response. It is therefore critical to identify pts with a low likelihood of response to anti-PD1-based therapy and efficiently assess activity of rationally-selected alternative novel immunotherapies. Methods: We designed this investigator-initiated phase II PIP-Trial to evaluate two consecutive biomarker testing platforms, followed by the activity of rationally selected 5 novel agents in pts with advanced melanoma. Two separate pt populations are included: Part-A) treatment-naïve pts predicted to be resistant to either anti-PD-1 alone or combined with ipilimumab using Biomarker Test-1); and Part-B) pts who had progressed on 1 prior line of PD1-based therapy. Part-A) is a Bayesian adaptive multi-arm multi-stage design using response adaptive randomisation after a burn-in period where pts are randomised to the existing arms with equal probability. From then on, regular interim analyses will be carried out with the objective to either drop poorly performing arms or continue. Part-B) is an open platform without control that combined a selection and an expansion phase to identify best novel agent(s) as second-line therapy. Expansion phase decisions will be based on enrichment for biomarker Test-2. Dropping an arm occurs when the posterior probability of observing a clinically significant effect on the primary outcome (i.e. 6-month RECIST objective response rate (ORR)) is low. The operational characteristics of the design were investigated through simulations considering 4 plausible scenarios with 40% ORR in the control arm (anti-PD1 + Anti-CTLA4). Simulations were based on the upcoming R package BATS. Part-A has at least 85% power to detect a 30% absolute improvement in ORR with respect to the control arm (with a max N = 216 – Table below). Part-B will be able to select two promising treatments in the expansion phase and formally test their efficacy against a minimum ORR of 25% at 80% power (max N = 150). [Table: see text]

9539 Background: Neoadjuvant IPI + NIVO induces high pathologic response rates (pRR) of 74-78% in macroscopic stage III melanoma. Pathologic response ( < 50% viable tumor) is strongly associated with improved relapse-free survival (RFS); the previous OpACIN-neo study demonstrated a 2-year RFS of 96.9% in patients (pts) with pathologic response, whereas the 2-year RFS in non-responders was 35.5%. These data highlight the need for baseline biomarkers predictive for response and survival. Here, we present the predictive value of the 10-gene IFN-y expression signature algorithm (based on Ayers et al.) for pathologic response and relapse in a cohort of melanoma pts treated with neoadjuvant IPI + NIVO. Methods: Baseline tumor biopsies from lymph node metastases of stage III melanoma pts were used for IFN-y signature assessment. Pts were treated with a maximum of two cycles of neoadjuvant IPI 1mg/kg + NIVO 3mg/kg in the OpACIN-neo (arm B) and PRADO studies. RNA expression analysis was conducted using the nCounter® PanCancer Immune Profiling panel on the NanoString Flex machine (NanoString Technologies), which is clinically applicable due to its fast turn-around-time (two days). An IFN-y signature gene expression score (IFN-y score) was calculated using a NKI-developed algorithm. Association between IFN-y score and pathologic response or event-free survival (EFS) was examined by logistic regression and Cox analyses. The optimal cutoff between a high and low IFN-y score was defined based on a summary receiver operating characteristic (sROC) curve. Results: In total, 103 pts treated in the OpACIN-neo and PRADO studies had baseline tumor material available. Median age was 56 years, 62% was male, and 52% had a high baseline IFN-y score. The pRR of the total cohort was 70% (72/103 pts), including 56% (58/103) major pathologic response (MPR, 0-≤10% viable tumor) and 14% (14/103) partial responses (pPR, 10-≤50% viable tumor). 30% (31/103 pts) had no pathologic response. After a median follow-up of 25.2 months, 26 pts (25.2%) developed a melanoma relapse. The IFN-y score was significantly associated with response (OR 1.061, p < 0.001) and relapse (OR 0. 974, p = 0.029). The pRR was 89% (48/54) in pts with a high IFN-y score versus 49% (24/49) in those with a low IFN-y score (p < 0.001). Pts with a high IFN-y score were also less likely to develop a relapse (11% [6/54] versus 41% [20/49], p = 0.001). Conclusions: Pts with a high IFN-y score in pre-treatment biopsies are more likely to respond to neoadjuvant IPI + NIVO with favorable EFS. A rapid gene expression analysis enables the IFN-y score to be used in daily clinical practice to identify pts who might qualify for treatment escalation or de-escalation. The DONIMI study [NCT04133948] currently investigates different neoadjuvant treatment combinations in stage III melanoma pts based on their intratumoral IFN-y score.

TPS9605 Background: Adjuvant treatment with anti-PD1 therapy improves the recurrence free survival (RFS) in resectable stage III melanoma. The Checkmate-238 and KEYNOTE-054 trials respectively reported a 4-year RFS of 52.5% for adjuvant nivolumab and a 3-year RFS of 63.7% for adjuvant pembrolizumab. Despite these improved outcomes, a considerable proportion of patients have a relapse in the years after therapeutic lymph node dissection (TLND). The OpACIN trial showed that neoadjuvant treatment with nivolumab (NIVO) plus ipilimumab (IPI) is feasible and induces a stronger and broader T-cell response. The subsequent OpACIN-neo trial identified 2 cycles of NIVO 3mg/kg + IPI 1mg/kg as a neoadjuvant dosing scheme with decreased toxicity and preserved high pathologic response rates (77%), which was confirmed in the PRADO trial. A favorable 2-year RFS (83,6%) was achieved in the overall OpACIN-neo population, although patients with a pathological partial or non-response have a worse prognosis and may therefore benefit from additional adjuvant therapy. The efficacy of neoadjuvant checkpoint inhibition versus the current standard of adjuvant therapy needs to be confirmed in a phase III trial, before neoadjuvant therapy can be considered as a standard option for this patient population. Methods: This international, randomized phase 3 trial aims to compare the efficacy of neoadjuvant IPI + NIVO with adjuvant NIVO in macroscopic stage III melanoma. In total 420 patients diagnosed with recurrent or de novo melanoma, with at least one pathologically proven, clinically detectable lymph node (up to 3 in-transit metastases (ITMs) allowed), will be randomized to neoadjuvant or adjuvant treatment. The population will be stratified by BRAF mutation, continent and the presence of ITMs. Patients in arm A will receive 2 cycles of IPI 80mg + NIVO 240mg and will undergo TLND at week 6. In the case of pathological partial response or non-response, surgery will be followed by adjuvant NIVO (11 cycles) or adjuvant dabrafenib + trametinib (46 weeks) if BRAFV600-mutation is present. Patients in arm B will undergo upfront TLND followed by 12 cycles of NIVO 480mg. The primary endpoint will be the event free survival (EFS) defined as the time from randomization until progression to unresectable stage III or stage IV melanoma, recurrent melanoma, a new primary melanoma or death due to melanoma or treatment. Final analysis will be performed after 132 events have been observed, or at latest 2 years after the last patient is included. Baseline biopsies and blood samples (screening, week 0, 3, 6, 9 and 12) will be collected for translational research. Quality of Life questionnaires and electronic Patient Reported Outcomes will be collected using the Kaiku application. The first patient was enrolled on the 23rd of July 2021. Clinical trial information: NCT04949113.

9503 Background: Combination anti-PD(L)1 and BRAF/MEK-targeted therapy (TT) improves PFS in stage IV melanoma vs TT. In stage IV melanoma recent data suggest immunotherapy 1st until progression, rather than BRAF-TT, improves OS, and induction TT upfront adds little benefit. NeoTrio explored the optimal combination of BRAF-TT and anti-PD1 using the NAT platform in pts with stage III melanoma (NCT02858921). Methods: 60 pts with resectable, RECIST measurable stage III (no in-transit) BRAFV600-mutant melanoma were randomized 1:1:1 to 3 arms of 6 wks of NAT followed by complete lymph node dissection (CLND): A) Pembro ALONE (200mg Q3W x 2); B) SEQ - D+T (150mg bd + 2mg od) for 1 wk followed by pembro (200mg x 2); C) CON – D+T+pembro (doses as SEQ). Pts had 46 wks pembro post-CLND. Primary endpoint was the pathological response rate (pRR) and pathological complete response (pCR) at wk 6. Secondary endpoints; RECIST RR at wk 6, event-free survival (EFS), RFS, OS, adverse events (AE) and translational endpoints. Results: At data cutoff 2 Jan 2022, 20 pts per arm had similar baseline characteristics; overall 42% female, med age 53 yrs, 82% BRAF V600E, 62% clinical N1b. Med f/u was 20 months (95% CI 17-31). The pCR rate and pRR were highest in CON arm, and similar in ALONE and SEQ arms (Table). Events (progression before surgery, recurrence after surgery or death) were highest in ALONE arm at this 1st analysis (Table). Assessment of the durability of path response subtypes in each arm is ongoing. Most common Rx related AE were fatigue (65%, 70%, 70%, ALONE, SEQ and CON respectively), pyrexia (0%, 25%, 85%) and rash (50%, 35%, 35%). Gd 3/4 AE occurred in 30%, 25% and 55%, respectively; pyrexia and hepatitis were common in CON during NAT. Rx interruptions during NAT occurred in 0, 3 and 19 pts, respectively; 1, 0 and 8 pts permanently discontinued. Post NAT surgical operability was the same or improved in 81%. Longitudinal analysis of melanoma tissue, microenvironment and microbiome is ongoing. Conclusions: CON D+T+pembro achieved the highest pRR, pCR rate, but with greater toxicity. Recurrences were seen in those with pCR/near pCR in BRAF-TT containing arms, but not in pembro ALONE, in keeping with previous data of NAT with checkpoint inhibitors vs BRAF-TT. Short course of D+T prior to PD1 did not improve path response, despite previous translational data showing increased tumour infiltrating T-cells early-during treatment with D+T. Follow up is ongoing. Clinical trial information: NCT02858921. [Table: see text]

9501 Background: In the OpACIN-neo study, 2 cycles neoadjuvant (neoadj) IPI 1mg/kg + NIVO 3mg/kg (I1N3) have been identified as most favorable dosing scheme with a pathologic response rate (pRR) of 77% and 20% grade 3-4 irAEs. After 24.6 months median follow-up (FU), the 2-year (2y) RFS was 96.9% for patients (pts) with pathologic response versus 35.5% for non-responders (>50% viable tumor; pNR). These data raised the question whether therapeutic lymph node dissection (TLND) could be safely omitted in pts achieving a major pathologic response (MPR; ≤10% viable tumor) in their index node (ILN; largest LN metastasis at baseline), and if additional adjuvant (adj) therapy could improve the outcome of pNR pts. Methods: PRADO is an extension cohort of the phase 2 OpACIN-neo study aiming to confirm the pRR and safety of neoadj I1N3 and to test response-driven subsequent therapy. Pts with stage III melanoma were included to receive 2 cycles neoadj I1N3 after marker placement in the ILN. ILN resection was planned at week 6. Pts that achieved MPR in the ILN did not undergo TLND; pts with partial response (pPR; >10 – ≤50% viable tumor) underwent TLND; and pts with pNR underwent TLND and received adj NIVO or dabrafenib plus trametinib (D+T) for 52 weeks ±radiotherapy (RT). Primary endpoints were pRR in the ILN and RFS at 2y. The 2y RFS rates were calculated using a Kaplan Meier based method. Results: Between Nov 2018 and Jan 2020, 99 patients were enrolled and treated with at least 1 cycle of neoadj I1N3. We previously showed a pRR of 72% (95% CI 62 - 80), including 60 (61%) pts with MPR and 11 (11%) pts with pPR. TLND omission in MPR pts resulted in significant reduced surgical morbidity and improved quality of life. There were 27 non-responders of whom 6 developed distant metastasis before ILN resection. Of the other 21 pNR pts, 7 received adj NIVO, 10 adj D+T, 3 no adj therapy, and 1 was lost to FU. After a median FU of 27.9 months (data cutoff Jan 31, 2022), the estimated 2y RFS rate for MPR pts was 93.3% (95% CI 87.2 – 99.9), with 4/60 pts developing a regional relapse. Distant metastasis-free survival (DMFS) was 100%. Of the 11 pPR pts, 4 developed a relapse (all distant), resulting in a 2y RFS and DMFS rate of 63.6% (95% CI 40.7 – 99.5). The 2y RFS rate of the pNR pts was 71.4% (95% CI 54.5 – 93.6), and DMFS 76.2%. At data cutoff, relapse occurred in 2/7 pNR pts with adj NIVO and 3/10 with adj D+T. Final data cutoff is planned mid Feb, 2022. Conclusions: MPR pts in whom TLND was omitted showed a 2y RFS rate of 93.3% and DMFS of 100%, indicating that the ILN procedure and omitting adj therapy could become a safe approach in these pts. Adj systemic therapy in pNR pts seems to improve RFS as compared to historic control (OpACIN-neo), thus should be considered in this unfavorable pNR group. The DMFS rate of 63.6% observed in the pPR group advocates the consideration of adj therapy also for this subgroup in the future. Clinical trial information: NCT02977052.

3024 Background: Liver metastasis is a poor prognostic factor in several cancers and is associated with poor response to immunotherapy (IO) in melanoma and lung cancer. VEGFi have activity in hepatocarcinoma (HCC) and is hypothesized to be due the hypoxic microenvironment. Whether this is also true for liver mets is unknown. We sought to assess the efficacy of VEGFi in liver mets utilizing randomized-controlled clinical trials (RCTs) testing the efficacy of VEGFi, regardless of primary cancer site. Methods: Systematic searches of PubMed, Cochrane CENTRAL, and Embase were conducted from January 1, 2000, to January 1, 2022. All RCTs that compared a backbone of systemic therapy (chemotherapy [chemo] and/or IO and/or targeted therapy [TT]) or best supportive care (BSC) with vs without VEGFi in patients (pts) with liver mets from any cancer were selected. HCC trials were excluded. Study design, cancer type, number of pts, lines of treatment, study drugs and hazard ratios (HRs) with 95% CIs for overall survival (OS) and progression-free survival (PFS) were extracted. Pooled effects of VEGFi in pts with liver mets across different cancer types were estimated using random effect model with inverse variance. Heterogeneity between studies was assessed by I2 statistics. Sensitivity analyses were performed considering prespecified subgroups of trials. Results: 3170 pts with liver mets from 19 RCTs were included in this meta-analysis: 8 colorectal cancer, 4 non-small cell lung cancer, 4 renal cell cancer & urothelial cancer, 1 pancreatic cancer, 1 GIST and 1 gastric cancer. Backbone systemic therapy in these trials included: chemo (11), TT (2), IO (2), chemo+IO (1), chemo+TT (1); and 2 BSC trials. Moderate heterogeneity between studies for both PFS (I2= 55%) and OS (I2= 46%) was seen. The addition of VEGFi to standard systemic therapy or BSC was associated with superior PFS (HR = 0.61; 95% CI, 0.50-0.74; p < 0.0001) and OS (HR = 0.86; 95%CI, 0.76-0.99; p = 0.0334) in pts with liver mets, regardless of whether pts had only liver mets or concurrent other sites of mets. In the subset of RCTs with data on pts without liver mets, the benefit with VEGFi was more pronounced in patients with liver mets (HR = 0.56) vs those without liver mets (HR = 0.64) for PFS, but not for OS. Conclusions: The addition of VEGFi to standard management improved survival outcomes in pts with liver mets across different cancer types and warrants further investigation. VEGFi added to IO may be effective in pts with resistant liver mets.

9572 Background: OpACIN was the first trial testing neoadjuvant ipilimumab (IPI) + nivolumab (NIVO) versus the same combination given adjuvant. An unexpected high pathologic responses of 78% was observed in the neoadjuvant arm with a 2-year relapse-free survival (RFS) rate of 80%. The subsequent OpACIN-neo trial tested 3 different dosing schedules of neoadjuvant IPI + NIVO and identified 2 cycles IPI 1 mg/kg + NIVO 3 mg/kg q3w as most favorable schedule with a pathologic response rate of 77% and 20% grade 3-4 immune-related adverse events. Long-term data on the durability of the pathologic (path) responses upon neoadjuvant checkpoint inhibition are lacking so far. Therefore, we present here the updated RFS and overall survival (OS) data of both trials. Methods: In OpACIN 20 macroscopic stage III melanoma pts were randomized to receive either IPI 3 mg/kg + NIVO 1 mg/kg q3w 4 cycles adjuvant after lymph node dissection or split 2 cycles neoadjuvant and 2 adjuvant. In OpACIN-neo 86 macroscopic stage III melanoma pts were randomized to arm A (2x IPI 3 mg/kg + NIVO 1 mg/kg q3w, n=30), arm B (2x IPI 1 mg/kg + NIVO 3 mg/kg q3w, n=30), or arm C (2x IPI 3 mg/kg q3w followed by 2x NIVO 3 mg/kg q2w, n=26) followed by lymph node dissection in week 6. RFS and OS were estimated using Kaplan Meier method. All comparative efficacy endpoints are descriptive for OpACIN, since the trial was not powered for comparison of the arms. Results: After a median follow-up (FU) of 68.6 months for OpACIN (minimum FU of 59.8 months), median RFS and OS were not reached. Only 1/7 patients (pts) with a pathologic response on neoadjuvant therapy has relapsed. Estimated 5-year RFS and OS rates for the neoadjuvant arm were 70.0% (95%CI: 46.7-100.0) and 90.0% (95%CI: 73.2-100.0) versus 60.0% (95%CI 36.2-99.5) and 70.0% (95%CI: 46.7-100.0) for the adjuvant arm. After a median FU of 46.8 months for OpACIN-neo (minimum FU of 38.2 months), median RFS and OS were not reached. Of pts with path response on neoadjuvant therapy, 3/64 (4.7%) had an event (2 pts relapsed, 1 pt died due to toxicity), versus 14/21 (66.7%) without path response. This resulted in a 3-year RFS rate of 95.3% (95%CI: 90.3-100.0) for responding versus 36.8% (95%CI: 20.4-66.4) for non-responding pts (p

9580 Background: Neoadjuvant D+T has a high pathologic response rate and impressive short-term survival. The NeoCombi trial (NCT01972347) enrolled 35 patients with resectable stage III melanoma, with last patient commencing treatment April 19th 2017. We report 5-year outcomes from this trial. Methods: Pts received 12 wks neoadjuvant standard dose D+T, then 40 wks adjuvant D+T. Eligible pts were ≥ 18 yrs, ECOG PS ≤ 1 with clinical stage III BRAF V600E/K melanoma. CT and PET scans were performed at baseline and prior to surgery. Pathologic response was determined as per International Neoadjuvant Melanoma Consortium (INMC) criteria and defined as complete (pCR), near complete, partial (pPR) or no response (pNR). CT monitoring was continued 12 wkly thereafter to 2 yrs, then 6 monthly to 3 yrs, then as standard care. The primary endpoints were the complete pathological response (pCR) and RECIST response rate (rRR) at wk 12. Secondary endpoints included relapse free survival (RFS), OS, and toxicity. Results: 35 pts were enrolled, 6 with IIIB, 29 IIIC (7 ITM only) disease (clinical AJCCv7). At data cut August 17th 2021, median F/U was 60 mo (95% CI 56-72). No patients progressed in the neoadjuvant phase, and (49%) had a pCR, 1 near pCR, 6 pPR, 11 pNR. 5-year RFS, DMFS and OS data are shown in the Table. The majority of recurrences occurred within the first 2 years, with no recurrences beyond 3y. 21 patients recurred; 12 (57%) had first recurrence locoregional (6/12 subsequent distant recurrence) and 9 (43%) had first recurrence in distant sites (3/9 in brain). Locoregional recurrence was managed with surgery alone in 4/12, systemic therapy alone in 2/12, or both surgery and systemic therapy in 5/12 (4/5 had adjuvant systemic therapy), 1 pt was observed until distant recurrence. Subsequent systemic therapy in the 15 patients with a distant recurrence included PD-1 based immunotherapy (N=14) and BRAF targeted therapy (N=10). Conclusions: Neoadjuvant D+T in clinical stage III melanoma has impressive early activity, however patients remain at high risk of recurrence. Pathologic response can identify patients at the highest risk of recurrence, offering a chance of alternative adjuvant therapy in non-responders. Clinical trial information: NCT01972347. [Table: see text]

10536 Background: Many melanomas and keratinocyte cancers (KC) are preventable by reducing sun exposure and improving sun protection behaviors. Recent evidence indicates a melanoma prevention program involving personalized genomic risk information provision can reduce self-reported sunburns at 12 months in Australian adults with no history of melanoma. This was alongside genetic counselling and educational materials on skin cancer prevention and early detection. However, the economic impact of this approach was unclear. This study aimed to determine the cost-effectiveness of the program to prevent melanoma and KC. Methods: A decision-analytic Markov model was developed to simulate the lifetime cost-effectiveness of personalized genomic risk provision compared with standard prevention advice alone, from a health system perspective. We used data from the Melanoma Genomics Managing Your Risk Study Randomized Control Trial. Traditional risk was measured by a validated melanoma risk prediction model involving hair color, nevus density, history of non-melanoma skin cancer, family history of melanoma, level of sunbed sessions. Quality-adjusted life years (QALY) gained was the primary outcome measure used to estimate an incremental cost-effectiveness ratio (ICER). Both deterministic and probabilistic sensitivity analyses (PSA) were undertaken. Results: The cost of the genomic testing and risk counselling program was AUD$189 (USD$132) per participant. Genomic risk provision targeting high-traditional risk individuals was the most cost-effective lifetime strategy with an ICER of AUD$23,033 (USD$16,059) per QALY gained and an 80% probability of being cost-effective at a willingness-to-pay threshold of AUD$50,000, compared with standard preventive advice (Table). When genomic risk provision was extended to low-traditional risk groups the ICER was $43,746 (USD30,500) per QALY gained with a 45% probability of being cost-effective. Conclusions: Genomic risk provision targeted to individuals at high-traditional risk of melanoma is a cost-effective strategy for the prevention of melanoma and KCs. Long-term sustainability of the program’s effect should be examined in future research. Clinical trial information: ACTRN12617000691347. [Table: see text]

PURPOSE BRAF/MEK inhibition is a standard of care for patients with BRAF V600E/K–mutated metastatic melanoma. For patients with less frequent BRAF mutations, however, efficacy data are limited. METHODS In the current study, 103 patients with metastatic melanoma with rare, activating non-V600E/K BRAF mutations that were treated with either a BRAF inhibitor (BRAFi), MEK inhibitor (MEKi), or the combination were included. BRAF mutation, patient and disease characteristics, response, and survival data were analyzed. RESULTS Fifty-eight patient tumors (56%) harbored a non-E/K V600 mutation, 38 (37%) a non-V600 mutation, and seven had both V600E and a rare BRAF mutation (7%). The most frequent mutations were V600R (43%; 44 of 103), L597P/Q/R/S (15%; 15 of 103), and K601E (11%; 11 of 103). Most patients had stage IV disease and 42% had elevated lactate dehydrogenase at BRAFi/MEKi initiation. Most patients received combined BRAFi/MEKi (58%) or BRAFi monotherapy (37%). Of the 58 patients with V600 mutations, overall response rate to BRAFi monotherapy and combination BRAFi/MEKi was 27% (six of 22) and 56% (20 of 36), respectively, whereas median progression-free survival (PFS) was 3.7 months and 8.0 months, respectively ( P = .002). Of the 38 patients with non-V600 mutations, overall response rate was 0% (zero of 15) to BRAFi, 40% (two of five) to MEKi, and 28% (five of 18) to combination treatment, with a median PFS of 1.8 months versus 3.7 months versus 3.3 months, respectively. Multivariable analyses revealed superior survival (PFS and overall survival) with combination over monotherapy in rare V600 and non-V600 mutated melanoma. CONCLUSION Patients with rare BRAF mutations can respond to targeted therapy, however, efficacy seems to be lower compared with V600E mutated melanoma. Combination BRAFi/MEKi seems to be the best regimen for both V600 and non-V600 mutations. Yet interpretation should be done with care because of the heterogeneity of patients with small sample sizes for some of the reported mutations.

9543 Background: mMCC is a rare, aggressive neuroendocrine cancer which often occurs in older patients (pts) with multiple comorbidities. While initial response rates to ICI are high, optimal treatment duration, durability of response after treatment cessation and response to retreatment with ICI is unknown. Methods: mMCC pts from 12 international centres who received at least one dose of ICI and subsequently stopped treatment without progression for a minimum of 12 weeks were studied. Demographics, disease characteristics and treatment course were examined. Results: 40 pts with mMCC were included. Pt characteristics are summarised in Table. Median time on treatment was 13.5 months (range 1 to 35). Median time to best response was 4.5 months (range 1 to 17) and median time receiving treatment after best response was 8 months (range 0 to 29). 25 pts (63%) stopped primarily due to being in a complete or partial response (CR or PR), 9 (23%) due to toxicity and 6 (15%) due to other reasons, primarily pt choice or comorbidities. At time of discontinuation, 30 pts (75%) were in a CR, 8 (20%) in a PR and 2 pts (5%) had stable disease (SD). After a median follow up of 12 months from discontinuation, 14 pts (35%) have progressed (PD); 5 (36%) at a previous site, 5 (36%) at a new site and 4 (29%) at both. PD occurred after a median of 5.5 months (range 4 to 29) off treatment. 4 pts (29%) had a CNS recurrence, none of whom previously had CNS involvement. Pts in CR at time of discontinuation were less likely to progress (CR: 26% PD vs non-CR: 67% PD, p=0.044), but still had a considerable rate of PD (CR: 26%, PR: 57%, SD: 100%). Those who progressed had numerically less cycles of ICI prior to treatment cessation (17 vs 32, p>0.05). Baseline disease factors, time to best response and duration of treatment after best response were not associated with PD. ICI was restarted in 8 of 14 pts (57%) with PD, with response rate to retreatment of 75% (4 CR, 2 PR, 1 SD, 1 PD – pt with leptomeningeal disease). Median time to best response at retreatment was 3 months (range 2 to 7), with all responses ongoing after a median of 10 months back on treatment. 3 pts had an isolated site of PD successfully treated with radiation therapy and remain in remission off ICI. Conclusions: ICI responses in mMCC do not appear as durable off treatment as in other cancers, including in patients who achieve a CR. Ongoing treatment should be considered, though initial data on response to retreatment is promising.[Table: see text]

9530 Background: Ultraviolet (UV)-induced high tumor mutation burden (TMB) of NACM is associated with response to anti-PD-1 monotherapy (aPD-1). Anatomic location of the primary lesion (reflecting UV exposure) and race (reflecting eumelanin level) may serve as surrogates for TMB and be associated with varying response and irAE patterns. Methods: Pts with advanced NACM receiving aPD-1 between 2009-2019 were retrospectively analyzed from 5 institutions in the US, Australia and China. Best response, survival (PFS and OS), and organ/system-specific irAEs were compared by race (Caucasian [C] vs non-Caucasian [NC]) and primary anatomic site. Results: Among 697 patients, 616 were C, 81 were NC. Complete response rate (CRR) was 24.8% (95%CI, 21.4-28.4) and 2.6% (95%CI, 0.3-9.1) and ORR was 54.9% (95%CI, 50.9-58.9) and 15.6% (95%CI, 8.3-25.6) in C and NC, respectively (both P

9508 Background: Preliminary data from the ABC (76 pts) and CheckMate 204 (94 pts) trials showed that nivo and nivo+ipi have activity in active melanoma brain metastases, with durable responses in a subset of pts. Here, we report updated 5-yr data from all pts enrolled on the ABC trial (NCT02374242). Methods: This open-label ph2 trial enrolled 3 cohorts of pts with active melanoma brain mets naïve to anti-PD1/PDL1/PDL2/CTLA4 from Nov 2014-Apr 2017. Pts with asymptomatic brain mets with no prior local brain therapy were randomised to cohort A (nivo 1mg/kg + ipi 3mg/kg, Q3Wx4, then nivo 3mg/kg Q2W) or cohort B (nivo 3mg/kg Q2W). Cohort C (nivo 3mg/kg Q2W) had brain mets i) that failed local therapy, ii) with neuro symptoms and/or iii) with leptomeningeal disease. Prior BRAF inhibitor (BRAFi) was allowed. The primary endpoint was best intracranial response (ICR) ≥wk12. Key secondary endpoints were IC PFS, overall PFS, OS, & safety. Results: A total of 76 pts (med f/u 54 mo) were enrolled; median age 59y, 78% male. For cohorts A, B and C: elevated LDH 51%, 58% and 19%; V600BRAF 54%, 56% and 81%; prior BRAFi 23%, 24%, 75%. Efficacy and toxicity are shown in the table. There were no treatment-related deaths. 1/17 deaths in cohort A & 4/16 in cohort B were due to IC progression only. Conclusions: Nivo monotherapy and ipi+nivo are active in melanoma brain mets, with durable responses in the majority of patients who received ipi+nivo upfront. A study of upfront ipi+nivo+/-SRS is underway (NCT03340129). Clinical trial information: NCT02374242. [Table: see text]

9533 Background: First line IPI+PD1 induces long-term response in 36% of MM patients (pts); however, the majority of pts will progress and may require further treatment, which is yet to be established. We studied the patterns of progressive disease (PD) on 1st line IPI+PD1, and the management and outcomes in MM pts. Methods: Demographics, disease characteristics, nature of PD, subsequent treatments and outcomes were examined in MM pts with PD on 1st line IPI+PD1. Multivariable analyses (MVA) identified factors associated with patterns of PD: innate resistance (IR) = PD as best response or stable disease (SD) < 6 mo; acquired resistance (AR) = PD after initial response or SD ≥ 6 mo. Results: 310 MM pts from 14 melanoma centres were included; 208 (67%) had PD during and 102 (33%) after ceasing IPI+PD1. Overall med. progression-free survival (mPFS) was 2.8 mo (CI 95% 2.7 – 3.0); 187 pts (60%) had IR (mPFS 2.2 [2.1 – 2.5]), 112 pts (36%) had AR (mPFS 8.5 [7.2 – 10.2]) and 11 pts (4%) had pseudoprogression, i.e. PD followed by response without changing treatment (mPFS 2.7 mo [1.4 – NA]). On MVA, pts with ECOG PS ≥ 1 were more likely to have IR vs AR; and within IR pts, those with head & neck primary melanomas and lung metastases were more likely to have PD < 1.5 mo. Most pts with IR (68%) had PD in multiple sites, while 61% AR pts had PD in a single site. Brain was most common site of single organ PD; 49% of IR and 41% of AR. Med. follow-up from PD was 32.7 mo (28.1 – 36.8). After PD, 61 pts (20%) had best supportive care (26% of IR and 11% of AR pts). 259 pts (80%) received further treatment: 39% IR pts had systemic treatment (ST) only and 27% had ST + local; 31% AR pts had ST only and 39% had ST + local. Of 200 pts (65%) who had ST(+/-local), 54% had 1 line of ST and 46% had ≥ 2; 1st line ST (ST1) was BRAF/MEKi in 36% of pts, PD1 in 32%, IPI+PD1 in 7%, investigational drugs in 11%, chemotherapy in 9% and others in 5%. ORR in IR pts was lower than in AR pts for every type of ST1 (see Table). Med. OS from PD was 11.4 mo (CI 95% 9.6 – 16.1); IR 6.4 mo (CI 95% 5.6 – 10.2) and AR 26.1 mo (CI 95% 17.1 – NA). Conclusions: These data suggest longer OS from PD for AR vs IR pts independent of ST type. BRAF/MEKi, rechallenge with PD1+/-IPI and investigational drugs showed activity after PD on IPI+PD1, while chemotherapy has no role in this context.[Table: see text]

9553 Background: Immune checkpoint inhibitors (ICIs) have activity across many tumor types, but activation of the immune system may also lead to significant, often steroid-refractory irAEs. We sought to determine the activity of tocilizumab, an anti-IL6R monoclonal antibody (mAb), in treatment or prevention of auto-immune irAE in ICI-treated patients (pts). Methods: Institutional databases from 2 melanoma centers were reviewed for pts treated with ICIs and tocilizumab. Treatment and melanoma outcomes were prospectively assessed. Longitudinal assessment of c-reactive protein (CRP) and assessment of clinical improvement (defined as irAE resolution to grade ≤1 CTCAEv5) or prophylaxis (absence of flare, defined as ≥ grade 2) were utilized to evaluate the benefit of tocilizumab. Paired Wilcoxon rank test was used to compare CRP levels prior to ICI administration, at the onset of irAEs and after tocilizumab administration. Results: 22 pts were identified. 2 pts were treated prophylactically (pre-existing dermatomyositis [n = 1] and giant cell arteritis [GCA, n = 1]) before the administration of PD1. 20 pts were treated for management of irAEs due to PD1 +/-CTLA4 (multiple concurrent irAEs [n = 3], steroid refractory irAES [hepatitis & pancreatitis, n = 2], steroid+anti-TNFα refractory colitis [n = 2], steroid+other immunosuppressive-refractory hepatitis [n = 1], cytokine release syndrome-related AEs [n = 6], musculoskeletal irAEs [n = 6]). 15 (68.2%) pts with irAEs required hospitalization and of those, 13 (86.7%) received tocilizumab whilst inpatient. Median time to irAE onset from ICI start was 48 days (range 8-786) and from irAE onset to tocilizumab administration 32 days (range 1-192). Median time to irAE resolution from tocilizumab administration was 7 days (range 1-799). Clinical improvement/benefit was demonstrated in 21/22 patients; one patient with ir-hepatitis did not respond. Median CRP prior to ICI administration was 32mg/L (range 0.3-99), at the onset of irAE 49.5mg/L (range 0.3-251, p = 0.055) and after the tocilizumab administration 18mg/L (range 0.3-18, p = 0.0015). Tocilizumab was well tolerated with self-limiting and transient toxicities in 17 (77.3%) patients. There were two grade 4 events; gastrointestinal tract perforation and Fournier gangrene, the latter unrelated to tocilizumab. Two (9%) patients died due to melanoma. From start of ICI, median progression-free survival (PFS) was 5.88 months and median overall survival (OS) was not reached. Conclusions: Tocilizumab was a well-tolerated and effective steroid-sparing treatment for both management of irAEs, as well as prevention of a flare of pre-existing auto-immune disorders during ICI administration. Prospective trials to evaluate its efficacy and impact on cancer outcomes compared with standard strategies are required.

10026 Background: Clinical trials of immunotherapy exclude patients (pts) with pre-existing AD. While retrospective data exist regarding the efficacy and safety of single agent ipi and anti-PD1 antibodies (PD1) in pts with AD, no data are available regarding the safety and efficacy of combination therapy in pts with AD, which has a higher toxicity risk. Methods: Pts with melanoma and pre-existing AD treated with combination ipi/PD1 were retrospectively identified from 10 international centres. Data regarding AD, treatment, toxicity and outcomes were examined. Results: Fifty-five pts were included, 46 were treated with ipi/nivolumab and 9 with ipi/pembrolizumab. 40 had an ipi dose of 3mg/kg while 15 had a lower dose regimen. 9 pts received prior PD1 therapy; 3 suffered moderate immune-related adverse events (irAE) with no flares of AD on single agent PD1. Pre-existing AD included inflammatory bowel disease (IBD), thyroiditis, rheumatoid arthritis (RA), multiple sclerosis and psoriasis. 10 pts had active symptoms of AD and 13 were immunosuppressed at commencement of ipi/PD1. Eighteen pts (33%) experienced a flare of their AD including 4/7 with RA, 3/6 with psoriasis, 5/9 with IBD, 3/18 with thyroiditis, 1/1 with Sjogren’s syndrome, 1/1 with polymyalgia, 1/1 with Behcet’s syndrome. Median time to flare was 19 days (range 4 – 167). 13 pts were managed with steroids, 5 required additional immunosuppressants. 7 pts were hospitalised for management of flare (5 with IBD, 2 with RA). 2 pts required intensive care and vasopressors for severe IBD flare, quiescent prior to ipi/PD1. One for diarrhoea and shock and one for duodenal perforation. 8 pts ceased treatment due to flare (3 with IBD, 2 with RA, 1 with Behcet’s, 1 with Sjogren’s). Thirty-seven pts (67%), experienced an irAE unrelated to their AD, 38% G3 or G4. The most frequent irAEs were colitis (n = 16), hepatitis (n = 12), endocrinopathies (n = 12), with 13 pts experiencing an irAE in ≥ 2 organs. 9 pts experienced both AD flare and an irAE. 20 pts (36%) ceased immunotherapy due to irAEs. ORR was 55% (54% in PD1 naive pts), at a median follow up of 14 months, 77% of responses ongoing. ORR in pts who had a flare of their AD was 44% and in pts on immunosuppression was 46%. Median PFS was shorter in pts who had a flare of AD compared with those who did not (2.6 vs 9 months; P-value 0.047). Conclusions: Combination ipi/PD1 shows efficacy comparable to clinical trial populations in pts with pre-existing AD and advanced melanoma. Whilst there was a substantial risk of flare of AD, no increased frequency of irAE’s was observed.

10005 Background: PD1 induces long-term responses in approximately 30% of MM pts, however 2/3 are resistant (innate or acquired) and will require further treatment. A subset of these pts will benefit from IPI or IPI+PD1, but these pts are yet to be identified. We sought to determine; i) response rate (RR) and survival to IPI+/-PD1 after PD1 progression, and ii) clinical predictors of response and survival to IPI+/-PD1. Methods: MM pts resistant to PD1 and then treated with IPI+/-PD1 were studied. Demographics, disease characteristics and baseline blood parameters were examined. Univariate, multivariate and backward elimination technique analyses were performed to create predictive models of response and overall survival (OS). Results: Of 330 MM pts resistant to PD1 (median time to prog 2.9 months [0.5 – 42.3], 12% adjuvant, 88% metastatic; 70% innate, 30% acquired), 161 (49%) had subsequent IPI and 169 (51%) had IPI+PD1. Characteristics at start of IPI+/-PD1 were similar in IPI vs IPI+PD1 groups (stage M1D 27% vs 34%; elevated LDH 38% vs 40%), except IPI group had more ECOG ≥1 (60% vs 34%) and less BRAF mutation (mut) (21% vs 37%). Median follow-up from start of IPI+/-PD1 was 22.3 months (19.8 - 25.8); RR was 22%, higher in IPI+PD1 (31%) vs IPI (12%) (p < 0.01). PFS and OS at 1 year were 20% and 48%, respectively; better with IPI+PD1 (27%/57%) vs IPI (13%/38%) (p < 0.01). PD1 setting (adjuvant/metastatic) and response did not impact response to IPI+/-PD1. Most pts progressing on adjuvant PD1 had IPI+PD1 (88%) and RR was 33%. Neither the interval between PD1 and IPI+/-PD1 nor use of other drugs affected response to IPI+/-PD1. RR was similar in BRAF WT (23%) vs BRAF mut (RR 21%) pts. In BRAF WT pts, RR was higher with IPI+PD1 vs IPI (38% vs 9%, p < 0.01), while RR was similar with IPI (24%) or IPI+PD1 (19%) in BRAF mut pts. One third of BRAF mut pts had BRAF inhibitors (BRAFi) prior to IPI+/-PD1 and lower RR (13%) vs those without BRAFi (RR = 25%, p > 0.05). High grade (≥G3) toxicity (tox) was similar with IPI+PD1 (30%) or IPI (34%, p = 0.48), and was not associated with response. Stage III/M1A/M1B, normal LDH and treatment with IPI+PD1 were the best predictors of response (AUC = 0.69). These factors, in addition to sex (male), ECOG PS = 0, BRAF mut, progressed/recurred > 3 months on PD1, and absence of bone mets were the best predictors of longer OS (AUC = 0.74). Conclusions: In pts resistant to PD1, IPI+PD1 has higher RR, longer survival, yet similar high grade tox than IPI alone. Predictive models of response & survival will help select pts for IPI+/-PD1 after progressing on PD1.

TPS10088 Background: Recent clinical trials of neoadjuvant (neo-adj) ipilimumab combined with nivolumab (OpACIN & OpACIN-neo) in resectable stage III melanoma show that a pathological response ( < 50% viable tumour at the tumour bed as determined by histopathological analysis) is associated with a prolonged relapse-free survival compared to no pathological response. Furthermore, recurrences seldom occur in those who have a pathological response following neo-adj immunotherapy with only 1/71 pts (1.4%) having recurred. In contrast, 15/23 (65.2%) pts with no pathological response have relapsed to date. The NeoPeLe trial will test the hypothesis that the synergistic combination of PD-1 blockade (pembrolizumab) with anti-angiogenic/multiple RTK inhibitor (lenvatinib) will result in a high rate of pathological response in the resected surgical specimen with a low rate of toxicity. Tissue and blood biomarkers are drawn at several timepoints and correlated to clinical and pathological endpoints to explore mechanisms of response and resistance. We will compare pathological response rate, and other clinical outcomes in this study, with previously published neo-adj clinical trials to select the best schedules for larger-scale clinical testing. Across neo-adj studies, we will also analyse the tissue collected to explore determinants of the optimal therapy for individual pts, whilst minimising toxicity. Methods: Eligible pts with stage IIIB/C/D, resectable and measurable (RECIST 1.1) nodal metastatic melanoma will be enrolled to this phase II single-centre trial (n = 20). All pts undergo complete nodal resection (RES) at wk 6 following neo-adj therapy with pembrolizumab (200mg, IV, 3 wkly) and lenvatinib (20mg, oral, daily). Adjuvant therapy with pembrolizumab is given for 46 wks after RES. After 52 wks of the study treatment, pts will be followed for relapse and survival for 5 years. CT and FDG PET/CT are used to measure response and exclude progression in the neo-adj phase, and to monitor for recurrence during adj and post treatment phases. Blood and tumour samples are collected at baseline, day 8, RES and at relapse if feasible. Faecal samples are collected at baseline and before RES. The primary endpoint is the complete pathological response rate at RES following 6 wks of neo-adj therapy. Secondary endpoints include RECIST response, metabolic response, OS, RFS, safety/tolerability, surgical outcomes, quality of life, and biomarker analyses. Clinical trial information: NCTNCT04207086.

10015 Background: Early results of the OpACIN-neo study testing 3 different dosing schedules of neoadjuvant IPI + NIVO demonstrated that 2 cycles IPI 1mg/kg + NIVO 3mg/kg (IPI1NIVO3, arm B) was the most favorable schedule with 20% grade 3-4 immunotherapy-related adverse events (irAEs) and a pathologic response rate (pRR) of 77%. After a median follow-up (FU) of 8.3 months, none of the 64 patients (pts) with a pathologic (path) response ( < 50% viable tumor cells) versus 9/21 (43%) without a path response had relapsed. Here, we present the updated 2-year RFS, EFS and long-term toxicity data. Methods: In the phase 2 multi-center OpACIN-neo trial, 86 stage III melanoma pts with resectable and RECIST 1.1 measurable lymph node metastasis were randomized between 3 different dosing schedules of neoadjuvant IPI + NIVO: arm A: 2x IPI3+NIVO1 Q3W (n = 30), arm B: 2x IPI1+NIVO3 Q3W (n = 30), and arm C: 2x IPI3 Q3W followed by 2x NIVO3 Q2W (n = 26). Lymph node dissection was scheduled at week 6. Primary endpoints were toxicity, radiologic RR and pRR; RFS and EFS were secondary endpoints. Results: After a median FU of 24.6 months, the median RFS and EFS was not reached in any of the 3 arms. In total, 2 pts progressed before surgery, 12 pts relapsed (11 pts without path response and 1 pt with pCR) and 5 pts died (4 due to melanoma and one pt due to toxicity). Estimated 24-months RFS was 84% (95% CI 76-92%) for the total population, 97% (95% CI 93-100%) for pts with a path response and 36% (95% CI 17-74%) for pts without a path response. Estimated 24-months EFS for the total population was 82% (95% CI 74-91%). RFS and EFS did not differ between the arms. Of the 81 pts alive, 55 (68%) have ongoing irAEs; only 2 (3%) pts have ≥ grade 3 irAEs. Most frequent ongoing irAEs were vitiligo (35%), fatigue (14%), sicca syndrome (11%), rash (10%), arthralgia (7%) and endocrine toxicities (20%). 17 pts need hormone replacement therapy: 11 (14%) thyroid hormone and 7 (9%) hydrocortisone. No difference between treatment arms was observed. Ongoing surgery-related AEs were observed in 31 (38%) pts of which lymphedema was seen most frequently (17 pts; 21%). Conclusions: Extended follow-up data shows that 2 cycles of neoadjuvant IPI + NIVO without adjuvant therapy induces durable RFS. While almost no ongoing high-grade irAEs were observed, the majority of pts have low-grade ongoing toxicities. These outcomes strongly support the need to test 2 cycles of neoadjuvant IPI1+NIVO3 versus adjuvant anti-PD-1 in a randomized phase 3 trial. Clinical trial information: NCT02977052.

10050 Background: ctDNA detected by ddPCR predicts ICI response in MM, although its utility is limited to pts with known recurring mutations eg. BRAF, NRAS, KIT. We sought to overcome this limitation by using a next generation sequencing approach in BRAF V600 wild type (WT) MM pts. Methods: Plasma was collected at baseline and Week (wk) 6 in 35 BRAF V600 WT MM pts treated with ICI. Cell free (cf)DNA was analyzed using Guardant360 and only somatic non-synonymous and promoter variants were considered. Pts who failed cfDNA extraction at baseline were excluded (n = 3). Favorable ctDNA was defined as undetectable ctDNA at wk 6 and unfavorable ctDNA defined as detectable ctDNA at wk6. Response was according to RECIST at first restaging. Results: Of the evaluable 32 pts (64 plasma samples), median baseline cfDNA quantity was 33ng (range 4-657ng) and ctDNA was detected in 29/32 pts (91%). All 3 pts with undetectable baseline ctDNA had less than 10ng cfDNA compared to only 1/29 pts with detectable baseline ctDNA. Number of mutations identified in the 29 ctDNA-positive pts was 4 per pt (range 1-22). Response assessment was performed on 30 evaluable pts. Candidate driver mutation(s) in BRAF, NF1, or N/K/HRAS were identified in 26/30 pts. These mutations were often detected with other established mutations involved in tumorigenesis (eg. TERT promoter), or passenger mutations (eg. clonal hematopoiesis). Analysis of driver mutations revealed a sensitivity and specificity in predicting treatment failure of 92% and 93%, respectively (table). When all mutations identified were evaluated for treatment response, 9/18 responding pts retained some ctDNA at wk 6, although this never included TERT variants. The resulting sensitivity and specificity in predicting treatment failure changed to 100% and 50%, respectively, when all cfDNA variants were included. Conclusions: The extensive coverage of Guardant360 improves ctDNA detection in BRAF V600 WT MM pts, allowing non-invasive, rapid, and longitudinal assessment of response in a broader population. The expanded coverage also identifies passenger variants of potential non-MM origin, eg. clonal hematopoiesis, and with significant overlap with ctDNA, it is not possible to distinguish between the two in the circulation. We therefore recommend identification and monitoring of known cancer driver mutations only. [Table: see text]

TPS10087 Background: Previous OpACIN and OpACIN-neo studies, investigating neoadjuvant ipilimumab (IPI) plus nivolumab (NIVO), demonstrated high pathologic response rates (74-78%) and favorable long-term outcomes in patients (pts) achieving pathologic response; at 36 and 18 months follow-up, respectively, only 1/71 (1.4%) pts with response has relapsed. In contrast, pts without pathologic response (pNR) have a poor prognosis; 15/23 (65.2%) have relapsed so far. This emphasizes the need for baseline biomarkers predictive of non-response and new neoadjuvant treatment combinations for these pts. In our previous studies, baseline interferon-gamma (IFN-γ) signature low pts were less likely to respond to neoadjuvant IPI plus NIVO. The DONIMI study tests the combination of NIVO +/- IPI with domatinostat (DOM), a class 1 histone deacetylase inhibitor, according to the IFN-γ signature in the tumor. Based on the signature previously described by Ayers et al. we have developed a neoadjuvant IFN-γ signature algorithm that will be used for the first time to classify pts in this prospective trial. Methods: The aim of this two-center investigator-initiated phase 1b study is to assess the safety and feasibility of neoadjuvant NIVO +/- DOM +/- IPI in 45 stage III melanoma pts with RECIST 1.1 measurable de-novo or recurrent disease. IFN-γ signature high pts (n = 20) will be randomized (stratified by center) to Arm A (2 cycles NIVO 240mg q3wk) or Arm B (2 cycles NIVO 240mg q3wk + DOM 200mg twice daily (BID), d1-14, q3wk). IFN-γ signature low pts (n = 25) will be randomized to Arm C (2 cycles NIVO 240mg q3wk + DOM 200mg BID, d1-14, q3wk) or Arm D (2 cycles NIVO 240mg q3wk + IPI 80mg q3wk + DOM 200mg once daily (OD), d1-14, q3wk). Based on safety data of the first 5 pts in arm D, the remaining pts will be treated with either a higher dosing scheme (200mg BID, d1-14, q3wks), a lower dosing scheme (100mg OD, d1-14, q3wks) or the same dosing scheme (200mg OD, d1-14, q3wks). The primary endpoint is safety and feasibility. A treatment arm will be declared as not feasible if 2/5 or 3/10 pts cannot adhere to the preplanned time of surgery (week 6 +/- 1week) due to treatment-related adverse events. Biopsies (week 0, 3), blood samples (week 0, 3, 6, 12) and feces (week 0, 3, 6) will be collected for translational research. The first patient was enrolled on January 23th, 2020. Clinical trial information: NCT04133948.

10064 Background: Neoadjuvant ipilimumab and nivolumab induces high pathologic response rates of 74-78% (OpACIN and OpACIN-neo trial), thus the role of Therapeutic Lymph Node Dissections (TLND) in patients with major pathologic responses (MPR: pathological (near) complete response) is now unclear. In the PRADO trial, TLND was omitted in patients with MPR in their index lymph node ((ILN), the largest LN marked prior to neoadjuvant therapy). We sought to determine if less extensive surgery is associated with better Health Related Quality of Life (HRQoL). These are the first results of the comparison of HRQoL between patients undergoing a TLND or less extensive ILN excision. Methods: HRQoL was assessed with the European Organisation for Research and Treatment of Cancer QoL questionnaire-C30 (QLQ-C30). A generalized estimation equation was used to assess the difference in HRQoL outcomes between patients who underwent TLND (pathological non- and partial-responders, pNR/pPR) versus those who did not (pathological (near)complete responders, pNCR/pCR). Differences were adjusted for age, gender and follow-up (FU, in weeks), but not for pathological responses (pNR, pPR, pNCR & pCR). Differences in QLQ-C30 scores were classified as clinically important according to published guidelines. Results: A total of 49 patients from the PRADO study had reached at least 24 weeks FU, and were included in the first explorative analysis. The median age of this study population was 58 years (range, 22-84). Questionnaire completion rates were high: 94% at baseline, 100%, 90%, 88% at week 6, 12 and 24, respectively. Sixteen (33%) patients underwent TLND versus 33 (67%) who had ILN excision only. Over a FU period of 24 weeks, patients who underwent TLND scored significantly lower on global (68 vs 78, adjusted difference (diff) = -9.53, p = .005), physical (84 vs 94 diff = -11.1, p = < .001), emotional (69 vs 83, diff = -11.7, p = .001), role (70 vs 85, diff = -13, p = .004), and social functioning (81 vs 91, diff = -8.9, p = .016) and had a higher symptom burden of fatigue (35 vs 23, diff = 11.1, p = .004), insomnia (38 vs 18, diff = 16.6, p = .002) and financial impact (12 vs 4, diff = 7.9, p = .027) than patients undergoing ILN excision only. These differences were indicated as clinically relevant. Conclusions: First results from PRADO suggest that reducing the extent of surgery following neoadjuvant immunotherapy might result in better HRQoL of high-risk stage III melanoma patients. Clinical trial information: NCT02977052.

10049 Background: Patients with advanced melanoma who progress on 1st line TT and 2nd line IT have limited treatment options. We explored the safety and efficacy of re-treatment with 3rd line TT. Methods: was pooled from 6 centers in Australia from 2009-2018. Eligible patients with BRAF V600 mutant melanoma had 1st line therapy with a BRAF/MEK inhibitor, 2nd line IO and were re-challenged with a BRAF/MEK inhibitor. Results: 90 patients were included; median age 61 years, 78% BRAF V600E, 89% ECOG 0-1 at baseline. 1st line TT was combination BRAF/MEK inhibitors in 80%, predominately dabrafenib/trametinib. Response to 1st line therapy was CR 20%, PR 41%, SD 17% and PD 13% and median duration of therapy was 7.2 months (0-33 months). 70% stopped for progressive disease, 9% toxicity and 16% had a planned switch to immunotherapy. For 2nd line IT, 49% had PD-1 alone, 33% had PD-1+CTLA-4, 14% had CTLA-4 alone. Only median duration on IT was 67 days (0-23 months), 81% ceased for PD, 14% for toxicity. Of patients who had a planned switch to IO before 1st line TT progression, one patient responded to second line IO with SD as BORR, there were no other responses to 2nd line IO in the planned switch group. At 3rd line TT re-challenge, 54% were AJCC stage IVd, 34% IVc, 51% had elevated LDH, 59% ECOG 0-1. 47% were re-challenged with dabrafenib/trametinib, 33% vemurafenib/cobimetinib, 11% encorafenib/binimetinib. BORR was 28%, with median duration on 3rd line TT 81 days. The OS was 1.7 years, with 34% alive at time of analysis. Conclusions: Despite progression on 1st line TT and 2nd line IT, patients may experience meaningful response and on re-challenge TT.

9514 Background: KEYNOTE-029 cohort 1B showed substantial efficacy for standard-dose pembro + 4 doses of ipi 1 mg/kg with lower rate of grade 3-5 toxicity than reported for standard-dose nivolumab + ipi in patients (pts) with advanced melanoma. In KEYNOTE-029 cohort 1C, we assessed the toxicity and antitumor activity of standard-dose pembro plus 2 alternate ipi doses (NCT02089685). Methods: Eligible pts with previously untreated stage III/IV melanoma, ECOG PS 0-1, and no active CNS metastases were randomized 1:1 to pembro 200 mg Q3W for 24 mo + 4 doses of ipi 50 mg Q6W (arm A) or pembro 200 mg Q3W for 24 mo + 4 doses of ipi 100 mg Q12W (arm B). Primary endpoints were the grade 3-5 treatment-related AE (TRAE) rate and ORR (RECIST v1.1, central review). With 50 pts per arm and compared with other anti–PD-1 + ipi regimens, a grade 3-5 TRAE rate ≤26% would suggest a meaningful reduction in toxicity and an ORR ≥48% would suggest no decrease in efficacy. Data cutoff date was Jul 17, 2018, and will be updated. Results: 102 pts were randomized: 51 to each arm. Median age was 63.5 y, 70% were male, 15% had ECOG PS 1, 34% had BRAF mutation, and 30% had elevated LDH at baseline. With 9.4 mo median follow-up, 69% of pts in arm A and 71% in arm B remained on treatment. All pts in arm A and 96.1% in arm B had ≥1 TRAE; grade 3-5 TRAE rates were 22% in arm A and 33% in arm B. 1 pt had a grade 5 TRAE (autoimmune myocarditis; arm A). ORR was 49% (95% CI 35-63) in arm A, including 7 CRs and 18 PRs, and 53% (95% CI 39-67) in arm B, including 6 CRs and 21 PRs. An additional 16 pts in each arm had SD or non-CR/non-PD, leading to a DCR of 80% and 84%, respectively. Median response duration was not reached in either arm (range 1.4+ to 9.6+ in arm A, 1.4+ to 9.8+ in arm B). Updated data based on longer follow-up will be presented. Conclusions: Standard-dose pembro + ipi 50 mg Q6W and standard-dose pembro + ipi 100 mg Q12W showed robust antitumor activity in this initial analysis. Both regimens appeared to have a lower rate of grade 3-5 TRAEs than previously observed. Longer follow-up and randomized studies are needed to confirm that these regimens reduce toxicity without compromising efficacy compared with other anti–PD-1 and ipi combinations. Clinical trial information: NCT02089685.

9583 Background: The efficacy of ICIs in metastatic melanoma is well-established. However, there is limited data regarding their efficacy in in-transit melanoma metastases (ITM). This study assessed the efficacy of ICI in patients with ITM. Methods: A multisite, retrospective review of patients with ITM treated with ICI from 2004-2018. Demographic and clinicopathological factors (age, sex, primary site, AJCC version 8 stage, BRAF status, prior locoregional therapies) were collected. Objective response rate (ORR) based on a clinician-assessed best overall response, progression free survival (PFS) and overall survival (OS) were analyzed by the Kaplan-Meier method. Results: Fifty-four patients were included: 27 (50%) female; median age 69 (range 19-89); 12 (22%) stage IIIB, 40 (74%) stage IIIC and 2 (4%) stage IIID; 10(19%) BRAF mutant. Forty (74%) received single agent PD-1 inhibitor (pembrolizumab or nivolumab), 8 (15%) single agent anti-CTLA-4 (ipilimumab), 5 (9%) combination anti-PD-1/anti-CTLA-4 (ipilimumab and nivolumab or pembrolizumab) and 1 (2%) combination anti-PDL-1/MEK inhibitor (atezolizumab and cobimetinib). ORR to ICI was 54%: 14 (26%) complete responses; 15 (28%) partial responses; 9 (17%) stable disease; 16 (30%) progressive disease. Thirteen (46%) responders had only one ITM lesion. ORR was 58% for single agent anti PD-1, 38% for single agent anti-CTLA4, and 40% for anti-PD-1/anti-CTLA-4 (Table). The median follow-up was 15 months (2-46). The median PFS was 11.7 months (6.6-N/A). PFS at 1 and 2 years were 48% and 39%. Fourteen (56%) progressed locoregionally and 11 (44%) progressed distantly. OS at 1 and 2 years were 85% and 63%; the median OS was not reached. No clinicopathological features were associated with ORR. Conclusions: ICI produces objective responses in ITM and should be considered in patients with unresectable ITM or disease recurrence despite locoregional therapies. [Table: see text]

TPS9605 Background: Adjuvant (adj) immune checkpoint inhibition (ICI) improves relapse free survival (RFS) in stage III melanoma patients (pts). However, preclinical and translational data suggest that neo-adjuvant (neoadj) treatment might be favorable due to broader immune activation. The phase 1b OpACIN study comparing neoadj to adj IPI plus NIVO demonstrated a high pathological response rate (pRR) of 78% complicated by 90% gr 3-4 immune-related adverse events (irAEs). The phase 2 OpACIN-neo trial tested safety and efficacy of three different schemes of neoadj IPI+NIVO and identified two cycles of IPI 1mg/kg + NIVO 3mg/kg as well tolerated (20% gr 3-4 irAEs), with a high pRR of 77%. In both trials, none of the pts with a pathologic response have relapsed after a median follow-up of 30 and 8.3 months. In stage IV melanoma, long-term benefit is observed in patients achieving CR with ICI, even after cessation of therapy. This raises the question of whether a therapeutic lymph node dissection (TLND) can be omitted when a deep pathologic response with neoadj IPI+NIVO is achieved. Methods: The aim of this international multi-center investigator-initiated phase 2 PRADO extension study is to confirm the pRR and toxicity of 2 cycles of neoadjuvant IPI 1mg/kg + NIVO 3mg/kg (the preferred OPACIN-neo regimen) and to test response-driven subsequent therapy i.e. omitting surgery and adjuvant ICI based on the pathological response. 100-110 pts with stage IIIB/C melanoma and a measurable lymph node (≥15mm according to RECIST 1.1) will receive two cycles of IPI 1mg/kg + NIVO 3mg/kg after marker placement into the largest lymph node metastasis. After six weeks, pts will undergo resection of the index lymph node. For pCR/near pCR, pts will not undergo TLND; For pPR, pts will undergo TLND; and for pNR, pts will undergo TLND and start adjuvant NIVO or targeted therapy +/- radiotherapy for 52 weeks. Primary endpoints are pRR of marked lymph node and RFS at 24 months. Baseline biopsies, blood samples (week 0, 6, 12) and faeces (week 0, 6) will be collected for translational research analyses. The first patient in this trial was included in October 2018; 22 patients have been enrolled. Clinical trial information: NCT02977052.

TPS9600 Background: Nivolumab combined with ipilimumab is active in melanoma brain metastases, with intracranial response rates > 55% and durable survival in treatment naïve patients (pts) (Long GV et al Lancet Onc 2018; Tawbi H et al NEJM 2018). We seek to determine if the addition of stereotactic radiotherapy (SRS) results in improved intracranial outcomes. Methods: This is a multisite, open-label, phase 2 trial in systemic treatment-naïve pts with melanoma brain metastases. Pts must have ≥1 asymptomatic brain metastases that are ≥5mm and ≤40mm as per modified RECIST 1.1, on gadolinium-enhanced MRI, and no history of previous treatment with SRS. Eligible pts are randomly assigned to either receive nivolumab plus ipilimumab with SRS or nivolumab plus ipilimumab alone. Nivolumab (1mg/kg) and ipilimumab (3mg/kg) are given every 3 weeks for 4 doses. Following induction, 480mg nivolumab is given every 4 weeks until progression, unacceptable toxicity, or a maximum of 2 years. SRS is administered as single fraction of 16-22Gy, or hypofractionated for larger lesions (24-27Gy in 3 fractions), within 7 days of immunotherapy commencement. Pts will be evaluated for intracranial and extracranial tumour response, and overall response, every 6 weeks to week 24 and 12 weekly thereafter until overall disease progression or death. The primary endpoint is neurologic specific survival (NSS) at 12 months. Secondary endpoints include intracranial response rate, intracranial PFS, overall PFS, overall progression free survival, overall survival, neurocognitive function and incidence of radiation necrosis. 109 patients in each cohort (218 total) will achieve > 80% power at the significance level (alpha) of 0.10 to detect a minimum absolute increase of 9% in the NSS rate at 12 months. Clinical trial information: NCT03340129.

9542 Background: Currently there are no robust biomarkers to predict immunotherapy response in MM. Specific clinical and molecular variables have been proposed, but in most cases, these factors have been studied individually. We sought to build a predictive model for response rate (RR), progression-free survival (PFS) and overall survival (OS), by including clinical data available at the point of treatment selection for MM pts treated with PD1 or IPI+PD1. Methods: 786 MM pts were included in 4 cohorts; 447 pts treated with PD1 (discovery, n = 343; validation, n = 104) and 339 pts treated with IPI+PD1 (discovery, n = 229; validation, n = 110). Demographics, disease characteristics and baseline blood parameters were examined. Predictive models were selected using multivariate Cox proportional hazard model, logistic regression and LASSO. ROC curve analyses were performed for each model and validation was measured by discrimination índex (c-statistic). Results: Predictive models for RR and PFS in PD1 pts (AUC = 0.69 and AUC = 0.71, respectively) included mutational status (HR for PFS: BRAF 1; NRAS 0.68; WT 0.57; P = 0.002), primary melanoma site (HR for PFS: occult 1; head and neck 0.67, others 1.04; P = 0.052), elevated LDH (HR for PFS: 1.77, P < 0.0001) and monocyte count > median (HR for PFS: 1.56, P = 0.003). Predictive models for RR and PFS in IPI+PD1 treated pts (AUC = 0.71 and AUC = 0.73, respectively) included AJCC stage M1C/M1D (HR for PFS: 2.12, P = 0.009), elevated LDH (HR for PFS: 2.65, P < 0.0001), liver mets (HR for PFS: 1.63, P = 0.038) and basophil count > median (HR for PFS: 0.50, P = 0.003). ECOG ≥ 1, elevated LDH and brain mets associated with worse OS and were included in predictive models for OS in PD1 (AUC = 0.74) and IPI+PD1 (AUC = 0.85). These models showed consistency with internal and external validation (c-statistic: < 10% difference between the original model and validations for all outcomes). Conclusions: A combination of routinely collected clinical factors are highly predictive of outcome in MM pts treated with PD1 and IPI+PD1. A prognostic index will be presented for each treatment. Such tools may be practical, cheap and valuable for clinical decision making.

9502 Background: Adjuvant anti-PD1 monoclonal antibodies (mAbs) prolong recurrence-free survival in high-risk resected melanoma, however patients (pts) recur during or after therapy. The patterns of recurrence and optimal management are unclear. Methods: Pts from 15 melanoma centres who recurred having received adjuvant anti-PD1 mAbs (adj-PD1) for resected stage III/IV cutaneous melanoma were included. Disease characteristics, adjuvant treatment, recurrence characteristics, subsequent management and outcomes were examined. Results: 137 pts had melanoma recurrence; 97 (71%) during adj-PD1 and 40 (29%) following treatment cessation (25 had stopped early for toxicity after a median 3 months, 14 after completing 12 months, 1 who withdrew consent after 1 month). Median time to recurrence from start of anti-PD1 was 4.6 months (IQR 2.7-8.5), and median follow up from recurrence was 7.7 months (IQR 3.8-12.3). At 1st recurrence, 78 (57%) pts had distant disease (including 22 with both locoregional and distant), 59 (43%) had locoregional disease only. Of those who recurred locally, 22/59 (37%) later developed distant disease. 26 (19%) pts have died. 81 (59%) pts had systemic therapy for distant recurrence (either 1st recurrence or subsequent). Of those who recurred during adj-PD1, no pts (0/20) subsequently responded to anti-PD1 alone (N = 8) or with any investigational agent (N = 12; anti-LAG3, IDOi, MEKi, TLR9 agonist); 9/27 evaluable pts (33%) responded to ipilimumab-based therapy (alone or in combination with anti-PD1), and 15/19 (79%) responded to BRAF/MEKi . Of those who recurred after ceasing adj-PD1, 2/5 (40%) responded to anti-PD1 monotherapy, 2/5 (40%) responded to ipilimumab-based therapy, 7/8 (88%) responded to BRAF/MEKi. Conclusions: These data suggest minimal activity of further anti-PD1 monotherapy in those who recur while on adj-PD1, but possible activity in those who recur off treatment. Anti-CTLA4 and BRAF/MEKi therapy appear active in those who recur on or following adj-PD1. Data on locoregional recurrence and its management will also be presented.

9581 Background: Brain mets are common in pts with MM, occurring in up 50% of pts. Serial ctDNA levels at baseline and early on therapy predict objective response (OR) and overall survival (OS) in MM pts without brain mets receiving immune checkpoint inhibitors (ICI). The predictive utility in pts with brain mets is unknown. Methods: BRAF/NRAS ctDNA at baseline and early on ICI therapy (week 3-8) was analysed using mutation specific digital droplet PCR (detection threshold 2.5 copies/ml plasma) in MM pts with brain mets. Intracranial (IC) and extracranial (EC) disease volume (sum of product of diameters of ALL mets [SPD]) and OR, progression-free survival (PFS) and OS were analyzed. Results: 48 pts with brain mets were studied, 40 with concurrent EC disease (SPD EC med 892mm2 [25-22417mm2], IC med 200mm2 [9-1487mm2]) and 8 with isolated IC mets (SPD med 150mm2 [66-1035mm2]). At baseline, ctDNA was detectable in 28 (58%) pts, 28/40 (70%) with IC + EC mets and 0/8 with isolated IC mets. Baseline ctDNA reflected EC disease volume (Pearson’s r = 0.4, p = 0.01) but not IC volume (r = 0.1, p = 0.5). Baseline ctDNA did not associate with IC or EC OR or PFS, however, undetectable ctDNA was associated with superior OS (HR 0.4, p = 0.01). Early on therapy, ctDNA predicted EC response but not IC response; EC OR was 65% if ctDNA undetectable and 6% if detectable (p < 0.01), IC OR was 35% if undetectable and 12% if detectable (p = 0.1). Nevertheless, undetectable ctDNA early on therapy was associated with a superior PFS (HR 0.3, p < 0.01) and OS (HR 0.2, p < 0.01), indicating survival is largely determined by extracranial disease activity. In the 8 pts with IC disease only, 7/8 had disease progressive disease as best response. 1/8 subsequently developed detectable ctDNA at week 12, with multiple new EC mets seen at first restaging scan at this time. Conclusions: ctDNA does not appear to be a useful biomarker for detecting brain mets nor monitoring brain response in melanoma pts receiving ICI. This has important implications when using ctDNA in the setting of surveillance in the metastatic and adjuvant setting.

9503 Background: Pathological complete response (pCR) to neoadjuvant systemic therapy (NST) correlates with survival, and is recognized as a path to regulatory approval in several cancers. Recent trials have reported that neoadjuvant immunotherapy (IT) and targeted therapy (TT) regimens achieve high pCR rates and impressive recurrence-free survival in stage III melanoma, however, the relationship between pCR, relapse-free (RFS) and overall survival (OS) in larger datasets of melanoma patients (pts) remains unknown. Methods: We pooled data from 6 modern NST clinical trials of anti-PD-1 based immunotherapy or BRAF/MEK targeted therapy conducted across institutions participating in the INMC. Pts with RECIST measurable, surgically resectable clinical stage III melanoma who underwent surgery were included. NST regimens included nivolumab (as monotherapy or in combination with ipilimumab), pembrolizumab or dabrafenib+trametinib. Baseline disease characteristics, treatment regimen, pCR and RFS were examined. Results: 184 pts with clinical stage III melanoma (AJCCv7: 100 IIIB, 84 IIIC) completed NST (133 IT, 51 TT) and underwent surgery. Median age was 57y (range 18-87). A pCR was observed in 41% of patients; 51 (38%) with IT and 24 (47%) with TT. Median follow-up post-surgery is 13 mo (95% CI 12-16); 10 mo with IT and 22 mo with TT. 44 (24%) pts have recurred (17 loco-regional, 21 distant, 6 both sites at first recurrence), 18 (14%) after IT and 26 (51%) after TT. 12-month RFS was improved with IT vs TT (83% vs 65%, p < 0.001). For those with pCR, 7% have recurred, 0/51 (0%) after IT, 7/17 (41%) after TT. For those without pCR, 34% have recurred, 18/82 (22%) after IT and 19/27 (70%) after TT. 12-month RFS was improved in those with pCR vs without pCR (95% vs 62%, p < 0.001), including in those with IT (100% vs 72%, p < 0.001) and TT (88% vs 43%, p < 0.001). 16 (9%) patients have died including two who had a pCR, both from TT. Conclusions: Neoadjuvant IT and TT are active regimens in resectable clinical stage III melanoma patients and are associated with high pCR rate. The ability to achieve pCR correlates with improved RFS and remarkably no patient with pCR from immunotherapy has recurred to date.

9511 Background: Several factors have been proposed as biomarkers for response to PD1 therapy, including tumor mutational burden (TMB), immune gene expression, PD-L1 expression and TILs, while few specific mechanisms of resistance have been identified. The relative importance of these factors or detailed examination of biomarkers of response to combination immunotherapy have yet to be explored. Methods: Cutaneous metastatic melanoma (MM) patients (pts) treated with anti-PD-1 (PD1) +/- anti-CTLA-4 (CTLA4) were selected. Pre-treatment tumors underwent whole genome sequencing (WGS), RNA sequencing (RNAseq) and immunohistochemistry (IHC; TILs and PD-L1). Results: Tumors from 77 pts treated with PD1 (n = 53) or PD1+CTLA4 (n = 24) underwent WGS. Higher TMB (p = 0.0001), lower structural variant (SV) burden (p = 0.001) and higher neoantigen load (p = 0.001) were associated with response. There was no difference in the expression of specific genes reported to confer resistance (JAK1/2, PTEN or BAF/PBAF complex members) or response (SERPINB3/4, ARID) in responders vs non-responders. RNAseq was performed on 53/77 samples; IFN and TCR signalling pathways were enriched in responders. Cytolytic activity (CYT, p = 0.002), T cell proportion estimated by CIBERSORT (p = 0.002) and confirmed by IHC (p = 0.033), and PD-L1 expression (IHC, p = 0.026) were also higher in responders. Multivariate analysis including DNA (TMB, SV count), RNA (six gene IFN expression signature - IFNG.6; effector T cell gene expression signature; chemokine gene expression; CYT), IHC (PD-L1, TILs) and clinical factors (sex, age, RECIST Sum of diameters, LDH) identified TMB and IFNG.6 as independent predictors of response (AUC = 0.83). 15 outliers with discordant molecular features and clinical outcomes had varying profiles, including 5 non-responders with high TMB, but low IFNG.6 expression, suggestive of a failure of immune activation. Conclusions: Comprehensive clinical and genomic analysis demonstrated that TMB and IFNG expression independently predict response, suggesting defects in both immune recognition or activation in non-responders.

9564 Background: Melanoma is one of the most common malignancies diagnosed during pregnancy. Little is known about the clinical outcomes of PAM, in particular, response to ICIs. We performed a retrospective study to assess this issue. Methods: A multicenter retrospective study was performed at 4 large melanoma centers. Patients (pts) with PAM treated with ICIs were identified and examined. Clinical data and molecular data (RNA sequencing, IHC) were explored. PAM was defined as development of advanced melanoma during pregnancy or within 2 years post-partum. Results: 19 pts with PAM were treated with ICIs. Median follow-up was 11.7 months (range 1.4 – 41.9 months). Median age was 29 years (range 16-36). Most pts had a cutaneous primary (N = 17, 89%) including the extremity (N = 8) or trunk (N = 7), and 5% were occult. 11 pts (58%) had a BRAF V600E mutation and 6 (32%) pts received BRAF/MEK targeted therapy. Most pts had prior primary melanoma (N = 12, 63%) and presented with advanced melanoma in the post-partum setting (N = 11, 58%). At advanced presentation, 6 (32%) pts were stage III/M1a and 13 (68%) pts were stage M1b/c/d; 7 (41%) pts had elevated LDH and 13 (68%) had visceral involvement. Among 11 patients treated with combination ipilimumab + anti-PD-1 therapy, 7 (64%) had objective responses (OR) with a 1-year progression free survival (PFS) of 40% and 1-year overall survival (OS) of 100%. By contrast, ICI monotherapy (3 with anti-PD-1/L1 and 4 with ipilimumab) was associated with poorer outcomes (OR in 25% and 33% for ipilimumab and anti-PD-1/L1, respectively). Molecular features (RNA sequencing, immunohistochemistry) will be presented. Conclusions: Patients with PAM represent a unique population and may particularly benefit with combination ICI therapy compared with ICI monotherapy (in a limited sample size). Molecular underpinnings of PAM biology are still being elucidated.

Purpose To assess the frequency and type of oncogenic BRAF mutations in metastatic melanoma and correlate BRAF status with clinicopathologic features and outcome. Patients and Methods Consecutive BRAF-tested Australian patients with metastatic melanoma (n = 197) were observed prospectively. A comprehensive range of clinicopathologic variables were correlated with BRAF mutation status, and a survival analysis was conducted. Results Forty-eight percent of patients had a BRAF mutation; 70 patients (74%) had V600E, 19 (20%) had V600K, and six (6%) had other genotypes. Other than age at diagnosis of distant metastasis (median age, 56 v 63 years for BRAF-mutant v BRAF wild-type patients, respectively; P < .001), there was no significant difference in clinical features of patients with metastatic melanoma by mutation status. Features of the antecedent primary melanoma significantly associated with a BRAF mutation (P < .05) were histopathologic subtype, presence of mitoses, single or occult primary melanoma, truncal location, and age at diagnosis of primary tumor ≤ 50 years. The interval from diagnosis of first-ever melanoma to distant metastasis was not significantly different between BRAF-mutant and BRAF wild-type patients; however, the median survival of patients with newly diagnosed metastatic melanoma was 5.7 months for BRAF-mutant patients not treated with a BRAF inhibitor, 8.5 months for BRAF wild-type patients, and not reached for BRAF-mutant patients treated with a BRAF inhibitor. Conclusion V600K mutations comprised 20% of BRAF mutations. Characteristics of the antecedent primary melanoma and age at diagnosis differed in BRAF-mutant and BRAF wild-type patients. The presence of mutant BRAF had no impact on the disease-free interval from diagnosis of first-ever melanoma to first distant metastasis; however, it may have impacted survival thereafter.

9532Background: There are limited data regarding the best sequence of targeted and immunotherapy in patients (pts) with BRAF-mutant melanoma. Some studies suggest lower activity of immunotherapy af...

9562Background: Obesity has recently been associated with improved outcomes in male, but not female, MM pts treated with single-agent anti-CTLA4 and with single-agent anti-PD1 immunotherapy. Howeve...

9545Background: Combination ipi and nivolumab is approved for advanced melanoma and is in trials across oncology. Toxicity (tox) most often occurs 6-10 wks into treatment. Whether early tox is hard...

TPS9604Background: BRAF targeted and CTLA-4/PD-1 immunotherapies have high response rates and improve survival for patients (pts) with metastatic melanoma, however, most still die of this disease. ...

TPS9606Background: The outcome of high risk stage III melanoma patients (pts) is poor, with a 5 year overall survival (OS) rate of < 50%. Adjuvant (adj) high dose IPI significantly improves 5 year progression free survival (PFS) and OS and adj NIVO improves the median PFS even more. In stage IV pts, the combination of IPI and NIVO improves response rates (RR) and PFS compared to monotherapy, but at cost of higher toxicity. Neo-adjuvant (neoadj) treatment may be a favorable approach as immune checkpoint inhibition (ICI) is of greatest value at the moment of TCR triggering and therefore dependent on the amount of antigen. The phase Ib OpACIN study compared neoadj versus adj IPI plus NIVO. The pathological RR (pRR) was 80% in the neoadj arm, and to date after a median follow-up of 24 months, none of the responders has relapsed, while 4/10 pts have relapsed in the adj arm. Moreover, pts in the neoadj arm expanded more tumor-resident TCR clones than adj treated pts. Neoadj IPI+NIVO was feasible, but toxicity w...

9542Background: BRAF/MEK inhibition is standard of care in patients (pts) with a BRAF V600E/K mutated melanoma. Efficacy data for pts with less frequent BRAF mutations are limited so far. Methods: ...

9517Background: PD1 based therapy has durable clinical activity for some pts with MM, however there are few predictors of long-term response and the optimal duration of therapy is unknown. Whether ...

9540Background: Combined BRAF and MEK inhibition (BRAF-MEK) is a standard therapy for BRAF V600 mutant melanoma, but doses and adverse event (AE) profiles were defined in trials conducted largely b...

9518Background: Immune checkpoint blockade improves the survival of patients with metastatic melanoma, but many patients fail to respond to immunotherapy and the lack of accurate predictors of resp...

e21588Background: Immune checkpoint inhibitors are standard of care for most patients (pts) with MM, yet only a minority has durable disease control. CTX has limited activity when used first-line, ...

9508 Background: Nivolumab (nivo) and the combination of nivo + ipilimumab (ipi) improve response rates (RR) and progression-free survival (PFS) compared with ipi alone in clinical trials of metastatic melanoma pts, but pts with untreated brain mets were excluded. Brain mets are a major cause of morbidity and mortality in melanoma and their management is critical. We sought to determine the antitumour activity and safety of nivo and nivo+ipi in pts with active melanoma brain mets (NCT02374242). Methods: This open-label, ph II trial enrolled 3 cohorts of pts naïve to anti-PD1/PDL1/PDL2/CTLA4 from Nov 2014 - Feb 2017. Pts with asymptomatic melanoma brain mets with no prior local brain therapy were randomised to cohort A (nivo 1mg/kg + ipi 3mg/kg, Q3W x4, then nivo 3mg/kg Q2W) or cohort B (nivo 3mg/kg Q2W). Cohort C (nivo 3mg/kg Q2W) had brain mets 1) that failed local therapy (new +/- progressed in previously treated met), 2) were neurologically symptomatic and/or 3) with leptomeningeal disease. Prior BRAF inhibitor (BRAFi) was allowed. The primary endpoint was best intracranial response (ICR) ≥ wk12. Secondary endpoints were best extracranial response (ECR), best overall response (OR), IC PFS, EC PFS, overall PFS, OS, and safety. Results: A total of 66 pts (med f/u 14 mo) were included in this analysis of total 76 planned; median age 60y, 77% male. For cohorts A, B and C: elevated LDH 48%, 58% and 19%; V600BRAF 44%, 56% and 81%; prior BRAFi 24%, 24%, 75%. Table shows RR, PFS and OS. ICR in cohort A treatment naïve vs prior BRAFi was 53% vs 16%. Treatment-related gd 3/4 toxicity in cohorts A, B and C were 68%, 40% and 56%, respectively. There were no treatment-related deaths. Conclusions:Nivo monotherapy and ipi+nivo and are active in melanoma brain mets. Ipi+nivo had reduced activity in pts who progressed on BRAFi. Pts with symptomatic brain mets, leptomeningeal mets or previous local therapy responded poorly to nivo alone. Clinical trial information: NCT02374242. [Table: see text]