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3510 Background: NIVO ± IPI is approved in previously treated pts with MSI-H/dMMR mCRC in the US, EU, and Japan, based on findings from the phase 2 CheckMate 142 study (NCT02060188). NCCN guidelines include NIVO + IPI as an initial therapy option for pts with MSI-H/dMMR mCRC. Results from a ~5-year follow-up from CheckMate 142 cohorts 1–3 (C1–3) are reported here. Methods: In this non-randomized, multicohort study, pts with MSI-H/dMMR mCRC were treated as follows: C1 (2L+; NIVO 3 mg/kg Q2W), C2 (2L+; NIVO 3 mg/kg + IPI 1 mg/kg Q3W [4 doses], followed by NIVO 3 mg/kg Q2W) and C3 (1L; NIVO 3 mg/kg Q2W + IPI 1 mg/kg Q6W), until disease progression or unacceptable toxicity. The primary endpoint was objective response rate (ORR) by investigator assessment (INV) per RECIST v1.1. Other key endpoints were disease control rate (DCR), duration of response (DOR), progression-free survival (PFS), all by INV and blinded independent central review; overall survival (OS), and safety. Results: In C1 (N = 74), C2 (N = 119), and C3 (N = 45), median (range) follow-up (time from first dose to data cutoff) was 70.0 (66.2–88.7), 64.0 (60.0–75.8), and 52.4 (47.6–57.1) months (mo), respectively. ORR (95% CI) by INV was 39% (28–51), 65% (55–73), and 71% (56–84; Table) and progressive disease (PD) rates were 26%, 12%, and 16% in C1, C2, and C3, respectively. Median DOR was not reached in the 3 cohorts. The 48-mo PFS rates were 36%, 54%, and 51% and 48-mo OS rates were 49%, 71%, and 72% in C1, C2, and C3, respectively (Table). PFS and OS rates with up to 60 mo of follow-up will be presented. Safety data are shown in the table. Conclusions: With extended follow-up of ~5 years, NIVO ± IPI continued to demonstrate durable OS and PFS benefit, with no new safety signals. These updated data further support current treatment recommendations for 2L+ NIVO ± IPI and 1L NIVO + IPI for pts with MSI-H/dMMR mCRC. Clinical trial information: NCT02060188. [Table: see text]

TPS226 Background: Despite recent improvements, management of locally advanced rectal cancer (LARC) remains challenging, and many patients (pts) still experience recurrence. In preclinical models, combining Rego with an anti-PD-1 inhibitor led to superior tumour growth suppression as compared with either treatment alone. In a phase I clinical trial, remarkable results were reported for the combination of Rego and Nivo in advanced MSS colorectal cancer. This synergistic effect is thought to be secondary to the anti-angiogenic effects of Rego and its potential to reduce TAMs, promote M1 macrophage conversion, and down-regulate expression of immunosuppressive factors. Building on these data, we designed a trial of Rego-Nivo with standard SCRT in the neoadjuvant setting of RC. Methods: REGINA is an academic, multicentre, single-arm, phase II trial sponsored by Institut Jules Bordet. Eligible patients are treated according to the following plan: induction phase (Nivo 240 mg IV D1&15, and Rego 80 mg PO D1-14), SCRT (D22-26), consolidation phase (Nivo 240 mg IV D29,43&57, and Rego 80 mg PO D29-49), and surgery (7-8 weeks after SCRT). Key eligibility criteria include age ≥18 years, ECOG PS ≤1, adenocarcinomas below the peritoneal reflection, intermediate-risk, stage II-III tumour (ie, cT3/T4aNany or cT1-2N+, no involvement/threatening of the mesorectal fascia, no involvement of lateral pelvic lymph nodes) irrespective of microsatellite instability status. The primary endpoint is pathological complete response (pCR). Secondary endpoints include, among others, toxicity, compliance to treatment, pathological tumour regression grade, event-free survival, and overall survival. Subjects will be followed for recurrence and survival for 5 years after end of treatment visit. The study follows a Simon’s two-stage design (null hypothesis pCR = 12%, alternative hypothesis pCR = 24%; α= 5%, β= 20%) with a maximum of 60 pts to be enrolled. A safety interim analysis is planned after the first 6 pts have completed treatment. Serial collection of tumour, blood, and stool samples is mandatory at pre-specified time points for exploratory correlative biomarker analyses. The trial is planned to be run at 8-10 centres across Belgium. Study recruitment started in Q1 2021 and is anticipated to complete in Q3 2023. The study is funded by Bayer. Clinical trial information: NCT04503694.

3600 Background: ctDNA is an indicator of minimal residual disease and negative prognostic factor in stage II-III CC treated with surgery +/- adjuvant chemotherapy (CT). No study, however, has ever analysed the prognostic value of this biomarker in CC patients (pts) treated with NACT. We sought to evaluate the prognostic value of baseline and early changes of cf/ctDNA in stage II-III CC pts who were treated with one cycle of NA FOLFOX CT followed by surgery +/- adjuvant FOLFOX CT in the PePiTA trial. Methods: PePiTA was a multicentre, single-arm, prospective phase II trial testing in vivo tumour chemosensitivity of early stage CC (as assessed by 18F-FDG PET/CT-based metabolic response to one cycle of NA FOLFOX) and its association with long-term outcome (NCT00994864). Plasma samples were prospectively collected at baseline, 2 weeks after one cycle of NA FOLFOX CT, and before surgery. NPY and WIF1 were selected as universal methylation markers for ctDNA and analysed with digital droplet (dd)PCR technology. Data from ddPCR were processed with the QuantaSoft v1.6 software (Bio-Rad). Survival outcome measures were 5-year disease-free survival (DFS) and 6-year overall survival (OS). ROC curve analyses, Kaplan-Meier method, cox proportional hazards models and log-rank tests were used. Statistical analyses were carried out with SPSS v25.0 (SPSS Inc.). Results: 80 pts were included (44 ypStage I-II and 36 ypStage III). After a median follow-up of 52.5 months, 5-year DFS and 6-year OS were 68% (95%CI 52-84) and 84% (95%CI 74-94), respectively. Pts with high (≥1600 ng/ml) baseline cfDNA had worse 6-year OS (HR 6.45, 95%CI 1.61-25.84; p = 0.008). Early changes of cfDNA after one cycle of NA FOLFOX CT failed to predict survival (HR DFS 0.96, 95%CI 0.38-2.43; p = 0.92; HR OS 0.62, 95%CI 0.16-2.50; p = 0.50). At baseline, 25 out of 60 (42%) ctDNA-assessable patients were positive. Detectable ctDNA at baseline (HR DFS 2.06, 95%CI 0.65-6.49; p = 0.22; HR OS 3.11, 95%CI 0.57-16.99; p = 0.19) or at any timepoint before surgery (HR DFS 1.65, 95%CI 0.54-5.04; p = 0.38; HR OS 2.80, 95%CI 0.54-14.44; p = 0.22) was not significantly associated with survival. A trend toward a significant association between ctDNA increase at surgery and 5-year DFS was found (HR 3.66, 95%CI 0.81-16.44; p = 0.09). Data on the correlation between early changes of cf/ctDNA and 18F-FDG PET/CT-based metabolic response will be presented at the meeting. Conclusions: For the first time, we have shown that baseline cfDNA may predict survival outcome in early stage CC pts treated with NACT. Pending confirmation in larger series, testing for cfDNA at baseline could help select high-risk pts who may benefit from FOxTROT-like, NACT treatment strategies. While analysis of ctDNA in this setting did not appear useful to predict prognosis, these results might be secondary to the small sample size.

74 Background: CYAD-101 is a first-in-class, non-gene edited allogeneic CAR T-cell product that combines the broad breadth of tumor targeting of the NKG2D-based chimeric antigen receptor (CAR) with a peptide-based approach that controls graft versus host disease (GvHD). NKG2D binds eight ligands commonly over-expressed across many tumors while the co-expressed T-cell receptor (TCR) inhibitory (TIM) peptide interferes with signaling by the endogenous TCR. A bank of CYAD-101 cells was produced from a single donor and evaluated in the AlloSHRINK phase 1 study (NCT03692429) in patients with unresectable metastatic colorectal cancer (mCRC). Methods: Three CYAD-101 infusions, each administered following a FOLFOX standard cycle as preconditioning chemotherapy, were tested in a 3+3 dose-escalation study (dose-levels (DL): 108, 3x108 and 109 T-cells per infusion) in patients with relapsed/refractory mCRC who progressed after previous treatment with oxaliplatin-based chemotherapy, with or without irinotecan-based chemotherapy. Results: Fifteen patients (pts) were enrolled (3 pts at DL-1, 3 pts at DL-2, 9 pts at DL-3). No dose-limiting toxicity (DLT), Grade ≥ 3 related adverse events or GvHD were reported after any of the CYAD-101 infusions, thus confirming the overall good safety profile of CYAD-101 post FOLFOX. Encouraging anti-tumor activity was observed with 2 confirmed partial responses (PR), including one response in a KRAS mutated patient. In addition, 9 pts achieved stable disease (SD), with 7 SD lasting at least 3 months. The median progression-free survival in this heavily pre-treated population was 3.9 months (95% CI). Whilst engraftment of the CYAD-101 cells was observed after each infusion, the relative level of systemic cytokines appeared to be primarily modulated by cell dose with some suggestion that the magnitude of modulation might be associated with clinical response. Interestingly, preliminary analysis of the T-cell repertoire identified some evidence of TCR diversity after therapy in the patient showing the most durable partial response. Conclusions: These clinical results demonstrate the safety and tolerability of a fist-in-human non-gene edited allogeneic CAR T-cell treatment with early promising anti-tumor activity in advanced mCRC pts. Preliminary translational analysis present intriguing observations that the modulation of systemic cytokine levels may be associated with dose which is uncommon in CAR T-cell therapies reported to date while limited T-cell clonal diversification in the best responding patient underscores the likely central role of the adoptively transferred T-cell in driving therapeutic response in this particular patient. Extension cohort evaluating CYAD-101 following other preconditioning chemotherapy is expected to be initiated end 2020. Clinical trial information: NCT03692429.

4040 Background: In the phase 2 CheckMate 142 trial, NIVO + low-dose IPI had robust, durable clinical benefit and was well tolerated as 1L therapy for MSI-H/dMMR mCRC (median follow-up 13.8 months [mo; range, 9–19]; Lenz et al. Ann Oncol 2018;29:LBA18). Longer follow-up is presented here. Methods: Patients (pts) with MSI-H/dMMR mCRC and no prior treatment for metastatic disease received NIVO 3 mg/kg Q2W + low-dose IPI 1 mg/kg Q6W until disease progression or discontinuation. The primary endpoint was investigator-assessed (INV) objective response rate (ORR) per RECIST v1.1. Results: In 45 pts with median follow-up of 29.0 mo, ORR (95% CI) increased to 69% (53–82) (Table) from 60% (44.3–74.3); complete response (CR) rate increased to 13% from 7%. The concordance rate of INV and blinded independent central review was 89%. Median duration of response (DOR) was not reached (Table). Median progression-free survival (PFS) and overall survival (OS) were not reached, and 24-mo rates were 74% and 79%, respectively (Table). Nineteen pts discontinued study treatment without subsequent therapy. An analysis of tumor response post discontinuation will be presented. Ten (22%) pts had grade 3–4 treatment-related adverse events (TRAEs); 3 (7%) had grade 3–4 TRAEs leading to discontinuation. Conclusions: NIVO + low-dose IPI continued to show robust, durable clinical benefit with a deepening of response, and was well tolerated with no new safety signals identified with longer follow-up. NIVO + low-dose IPI may represent a new 1L therapy option for pts with MSI-H/dMMR mCRC. Clinical trial information: NTC02060188 . [Table: see text]

3032 Background: In contrast to autologous CAR-T cell therapies, allogeneic donor-derived CAR-T cells can be banked and used in a timely fashion overcoming the critical time delay of just in time autologous cell manufacture. CYAD-101 is an allogeneic CAR-T that uses a non-gene edited peptide-based technology (TIM) to control graft versus host disease (GvHD) combined with a NKG2D-based CAR. Pre-clinical studies confirmed that CYAD-101 maintained CAR-directed anti-tumor activity in the absence of the induction of GvHD. Clinical grade CYAD-101 cells were produced for the phase 1 alloSHRINK trial (NCT03692429). Methods: A bank of clinical grade CYAD-101 cells was generated through two production runs using a single donor apheresis. Together, the bank generated > 53 billion CYAD-101 cells suitable for the entire dose escalation segment and short expansion phase of the trial (15 patients in total). Both runs showed high consistency with the CYAD-101 product generated composed mainly of CD4+ T cells (>85%) with a transduction level of > 92%, low relative expression of CD69/CD25 and largely absent expression levels of PD-1/LAG-3. The CYAD-101 cells were predominantly (>80%) CD45RA−/ CD62L−/ CD27− suggestive of an effector memory T cell population. Results: Upon co-culture with target K562 cells, CYAD-101 readily produced IFN-γ that was blocked by a NKG2D blocking antibody confirming specificity of the CAR. CYAD-101 cells showed in vitro cytotoxicity against tumor cells and produced an array of Th1 (IFN-γ, IL-2 and TGF-β) and Th2 (IL-4, IL-5) cytokines. Importantly, minimal IFN-γ was produced upon TCR stimulation while stimulation with a non-TCR mitogen (PMA + ionomycin) lead to high levels of IFN-γ. Together, these data show that clinical grade CYAD-101 cells were able to functionally respond through the CAR but showed minimal TCR-driven activation. Fifteen refractory metastatic CRC patients who had previously failed at least one line of oxaliplatin—containing therapy were treated with three doses of CYAD-101 cells given on Day 3 of three successive FOLFOX chemotherapy cycles. Updated clinical results continue to demonstrate an encouraging clinical activity (2 patients with partial response and 9 with stable disease) and the absence of GvHD in the context of CYAD-101 cell engraftment. Conclusions: These early clinical results demonstrate the safety and tolerability of a non-gene edited predominantly CD4+ CAR-T therapeutic approach. The initial observations of clinical activity in metastatic CRC patients warrants the continued development of this therapy. Clinical trial information: NCT03692429 .

e15093 Background: The identification of oligometastatic profile in patients with resectable colorectal liver metastases (CRLM) would represent a major progress to improve selection for surgery. Currently, in the absence of biomarkers, the most reliable method to identify oligometastatic (OLM) and non-oligometastatic (NOLM) tumors relies on the oncological outcome after metastases-targeted surgery. The histological growth pattern (HGP) of CRLM, defined as desmoplastic (dHGP) or replacement (rHGP), has recently been shown to have prognostic value. We analyzed HGP in a series of patients operated for CRLM, characterized as OLM in case of prolonged postoperative recurrence-free survival (RFS) or NOLM in case of rapid postoperative relapse. Methods: In 357 patients operated for CRLM, we identified OLM patients as those with RFS≥5 years (N = 64), and NOLM patients as those with RFS < 1 year (N = 77). Clinicopathologic and surgical parameters were analyzed. In each CRLM, HGP was assessed in archival H&E stained tissue sections, according to international consensus guidelines. Proportions of rHGP and dHGP were determined in each metastasis. In case of multiple metastases, the mean HGP was calculated in each patient. Patients were categorized as pure (> 95% rHGP or dHGP) or dominant phenotypes (> 50% rHGP or dHGP, of the entire tumor-liver interface). Results: Preoperative characteristics of primary tumor and CRLM, and surgical data were identical in OLM and NOLM groups. In a first set of analyses, HGP was determined in 39 OLM and 52 NOLM patients. Pure dHGP was observed in 54.3% of OLM and 17.3% of NOLM patients (p = 0.001). Pure rHGP was similarly distributed among OLM and NOLM groups. Sixty-nine% of the OLM patients displayed a dHGP-dominant phenotype, whereas 57.7% of the NOLM patients presented with a rHGP-dominant phenotype (p = 0.02). Conclusions: These results confirm the potential prognostic value of HGP in patients operated for CRLM. dHGP, associated with angiogenesis and inflammation, could represent a (surrogate) marker for oligometastatic progression, whereas rHGP appears strongly associated with rapid postoperative relapse.

3610 Background: Although being the standard-of-care for stage III colon cancer, no biomarkers can identify patients (pts) who benefit from adjuvant chemotherapy. In metastatic pts, the lack of metabolic response (mR) in FDG-PET/CT after 1 chemotherapy cycle predicts the absence of treatment benefit. The PePiTA study aims to evaluate if the absence of mR after 1 cycle of pre-operative chemotherapy is predictive of recurrence in non-metastatic colon cancer pts. Herein, we report a preliminary analysis on surgical outcomes, adverse events and mR assessment after 1 cycle of pre-operative chemotherapy after completing the study accrual objective. Methods: Colon cancer pts eligible for curative resection and ECOG ≤1 received 1 cycle of mFOLFOX followed by surgery in this prospective, multicentre, non-randomized trial. FDG-PET/CT was performed at baseline and after 1 cycle of mFOLFOX. Adjuvant mFOLFOX was administered for up to 12 cycles for stage III pts, whereas for stage II pts the decision to pursue adjuvant chemotherapy was at investigator’s discretion. A decrease ≥15% in SUVmax after 1 cycle of chemotherapy was defined as mR (EORTC criteria) at central review. Results: mR was assessable on the primary tumor in 204/240 pts (85%). In 11 pts (4.6%), staging was modified by the baseline FDG-PET/CT, which detected metastatic disease or other tumors. Pre-operative mFOLFOX was administered to 218 pts, of which 14 (6%) had a grade ≥3 adverse event. Surgery was performed in 218 pts, with a median delay of 20 days (6 to 59) after chemotherapy. Surgical complications occurred in 28 (13%) pts, however no deaths occurred. The median SUVmax decrease between baseline and 2nd FDG-PET/CT was 24%. A mR was observed in 65.2% of the pts, whereas 34.8% showed no mR, including 3% who had progressive disease. Conclusions: One cycle of pre-operative mFOLFOX followed by a mR assessment has shown to be a feasible and safe strategy, raising interest on the potential of neoadjuvant chemotherapy in colon cancer. The early mR assessment identified pts that may not benefit from chemotherapy and might have a worse prognosis. The substantiation of this hypothesis is expected with the study’s long-term results. Clinical trial information: NCT00994864.

3543 Background: This study aimed to develop and validate a prognostic score integrating baseline metabolically active tumor volume (MATV) and clinical factors in metastatic colorectal cancer (mCRC) patients. Methods: The development cohort included chemorefractory mCRC patients enrolled in two prospective multicenter non-randomized trials evaluating sorafenib/regorafenib as last line therapy. The validation cohort included mCRC patients from another center, treated with chemotherapy and bevacizumab as first line. Baseline MATV was defined as the sum of metabolically active volumes of all target lesions identified on the baseline 18F-FDG PET/CT. MATV optimal cutoff for OS prediction was determined from the development cohort with Contal and O’Quigley’s method. MATV, age, gender, BMI, ECOG PS, years since diagnosis, and KRAS status were included in a multivariate analysis. A prognostic score to predict OS was developed from the development cohort using Cox proportional hazards model. Results: MATV and clinical factors were evaluable respectively in 155 and 122 patients of the development and validation cohorts. In univariate analysis, MATV with cutoff set at 100 cm³ identified two risk groups with different median OS (mOS) in both the development (4.5 vs 10.9 months, HR: 2.64; p < 0.001) and validation cohorts (20.9 vs 42.9 months, HR: 2.39; p < 0.001). A multivariate analysis identified four independent negative predictors of OS (high MATV, short time since diagnosis, poor PS, BMI < 25). Combining these factors in a prognostic score for OS (best cutoff:-2) allowed to identify two risk groups with different mOS in the development (4.4 vs 13.4 months, HR: 3.67; p < 0.001) and validation cohorts (25 vs 63.8 months, HR: 2.5; p = 0.001). Conclusions: In mCRC patients, the high prognostic value of baseline MATV found in the development cohort was confirmed by external validation, independently of patients’ treatment. In both the development and validation cohorts the prognostic score for OS allowed to identify two risk groups of mCRC patients with significantly different mOS. MATV and our prognostic score for OS should provide a firm basis for risk stratification, in clinical practice and research trials.

4125 Background: LAPC is associated with a poor prognosis. Current standard treatment is limited to chemotherapy or chemo-radiotherapy. P-32 Microparticles is a brachytherapy device that implants a predetermined dose of P-32 into pancreatic tumours via endoscopic ultrasound (EUS) guidance. This reports the initial results of a pilot study in combination with chemotherapy. Methods: Eligible patients were permitted to receive either GNP or FOLFIRINOX. P-32 was implanted at week 4 or 5. The dose of P-32 was calculated from tumour volume to deliver an absorbed dose of 100 Gy. Diffusion pattern of the P-32 suspension was assessed by EUS and bremsstrahlung SPECT/CT imaging. Safety data was graded using CTCAE v4.0 criteria. Response was assessed according to RECIST 1.1 with CT scans every 8 weeks and FDG-PET scans at baseline and week 12. Results: 50 patients were enrolled (Intent-to-Treat population (ITT)) of which 42 were implanted with the device (Per Protocol population (PP)). 10 received FOLFIRINOX and 40 GNP. Median age was 65, 28 were male and all had a PS 0/1. 1070 adverse events (ITT) were reported; 153 (80% of patients) were ≥ Grade 3. The most common AEs of ≥ Grade 3 were haematological (39, 46%) and gastrointestinal disorders (30, 34%). No serious device- or radiation-related toxicities have been reported. PP Local Disease Control Rate at Week 16 was 90%; 95% CI: 77-97% and at Week 24 was 71%; 95% CI: 55-84%. Overall Response Rate (ORR) was 31%; 95% CI: 18-47%. Median change in tumour volume from Baseline to Week 16 and to Week 24 was -38% (range +89% to -90%) and -27.5% (range +139% to -79%). Ten (24%) patients underwent surgical resection following repeat staging. Eight patients had R0 margin. Conclusions: The use of EUS-guided implantation of P-32 is feasible, with an acceptable safety profile in combination with first-line chemotherapy for LAPC patients. Encouraging OR and DCR are observed. Further follow-up to inform results of local progression free survival and progression free survival is warranted. Acknowledgement: Nab-paclitaxel was supported by Specialised Therapeutics Australia Pty Ltd. Clinical trial information: NCT03003078.

e15094 Background: Selection for surgery in patients with colorectal liver metastases (CRLM) remains poorly accurate. We evaluated if baseline metabolic characteristics of CRLM, as assessed by [18]-fluorodeoxyglucose Positron Emission Tomography/Computed Tomography (18FDG-PET/CT), may predict the postoperative outcome in patients operated for CRLM. Methods: In a series of 450 patients operated for CRLM, we retrospectively identified 2 groups: The long-term survival (LTS), as defined by postoperative recurrence-free survival (RFS)≥5 years, and the early relapse groups (ER), as defined by RFS < 1 year. Clinicopathologic characteristics, Clinical Risk Score (CRS) and baseline 18FDG-PET/CT metabolic parameters were analyzed. Baseline 18FDG-PET/CT was performed at the time of diagnosis of CRLM, before any preoperative treatment. Low and high-risk CRS were defined by scores of 0 to 2 and 3 to 5, respectively. Metabolic CRS (mCRS) was implemented, using 1 additional point to the standard CRS when the highest tumor standardized uptake value (SUVmax) and normal liver mean SUV (SUVmean(liver)) ratio was > 4.3. Low and high-risk mCRS were defined by scores of 0 to 2 and 3 to 6, respectively. Results: We analyzed 53 patients. No difference was observed between LTS (n = 23) and ER (n = 30) groups for clinicopathologic parameters related to the primary tumor and CRLM, CRS and rates of low/high risk CRS. All metabolic parameters analyzed, including SUVmax and SUVpeak, at the exception of metabolic tumor volume, were significantly increased in ER group. Median SUVmax/SUVmean(liver) ratio was significantly increased in the ER vs LTS, respectively of 4.2 and 2.8 (p = 0.008). mCRS was significantly higher in ER as compared to LTS patients (p = 0.024), while 61% of the LTS patients had a low-risk mCRS and 73% of the ER patients had a high-risk mCRS (p = 0.023). Conclusions: Baseline 18FDG-PET/CT characteristics demonstrate an increased tumor glucose uptake in patients who rapidly recur after curative-intent surgery for CRLM. The introduction of these data into clinical risk model may represent a new tool to improve selection for surgery in patients with CRLM.

Purpose Liver dissemination is a major cause of mortality among patients with advanced colorectal cancer. Hepatic intra-arterial injection of the β-emitting isotope yttrium-90 (90Y) bound to resin microspheres (radioembolization) delivers therapeutic radiation doses to liver metastases with minimal damage to adjacent tissues. Patients and Methods We conducted a prospective, multicenter, randomized phase III trial in patients with unresectable, chemotherapy-refractory liver-limited metastatic CRC (mCRC) comparing arm A (fluorouracil [FU] protracted intravenous infusion 300 mg/m2 days 1 through 14 every 3 weeks) and arm B (radioembolization plus intravenous FU 225 mg/m2 days 1 through 14 then 300 mg/m2 days 1 through 14 every 3 weeks) until hepatic progression. The primary end point was time to liver progression (TTLP). Cross-over to radioembolization was permitted after progression in arm A. Results Forty-six patients were randomly assigned and 44 were eligible for analysis (arm A, n = 23; arm B, n = 21). Median follow-up was 24.8 months. Median TTLP was 2.1 and 5.5 months in arms A and B, respectively (hazard ratio [HR] = 0.38; 95% CI, 0.20 to 0.72; P = .003). Median time to tumor progression (TTP) was 2.1 and 4.5 months, respectively (HR = 0.51; 95% CI, 0.28 to 0.94; P = .03). Grade 3 or 4 toxicities were recorded in six patients after FU monotherapy and in one patient after radioembolization plus FU treatment (P = .10). Twenty-five of 44 patients received further treatment after progression, including 10 patients in arm A who received radioembolization. Median overall survival was 7.3 and 10.0 months in arms A and B, respectively (HR = 0.92; 95% CI, 0.47 to 1.78; P = .80). Conclusion Radioembolization with 90Y-resin microspheres plus FU is well tolerated and significantly improves TTLP and TTP compared with FU alone. This procedure is a valid therapeutic option for chemotherapy-refractory liver-limited mCRC.

3532Background: BL-cfDNA combined with plasmatic changes in tumor-specific mutations after 14 days of therapy are explored as independent determinants of outcome in pts with aCRC. Methods: Archival...

e15613Background: A substantial proportion of patients undergoing colorectal liver metastases (CRLM) resection with curative-intent will rapidly recur, emphasizing the need to improve the current s...

554 Background: Nivolumab (NIVO) provided durable responses (ORR, 32% per central assessment) and disease control (DCR, 64%) in pre-treated pts with dMMR/MSI-H mCRC (NCT02060188; Overman MJ et al Lancet Oncol 2017). NIVO was approved in the US for pts with dMMR/MSI-H mCRC who progress after standard chemotherapy (SC) with a fluoropyrimidine (F), oxaliplatin (Ox), and irinotecan (Iri). Here we present long-term survival and outcomes by prior chemotherapy with NIVO in CheckMate-142. Methods: Pts with dMMR/MSI-H mCRC received NIVO 3 mg/kg Q2W. The primary endpoint was ORR per RECIST 1.1. Other endpoints were DCR, DOR, PFS, OS, and safety/tolerability. Results: Of 74 pts evaluated, 53 had received F, Ox and Iri (group A); 21 pts had ≤ 2 SC regimens (group B). Median follow-up was 21 mo. Efficacy by central assessment is shown in the Table. In the 74 pts, ORR was 34%; CRs increased from 3% in prior database lock (DBL) to 9%. Numerically higher responses were noted in group B vs group A (Table). Grade 3–4 TRAEs were reported in 20% (all pts), 25% (group A), and 10% (group B) of pts. No treatment-related deaths were reported. Conclusions: NIVO continued to provide clinically meaningful durable responses and long-term overall survival in pts with dMMR/MSI-H mCRC. Of note, CR rate increased with longer follow-up. No new safety signals were reported with long-term follow-up. Enhanced responses in pts with ≤ 2 SC regimens support ongoing evaluation of NIVO combinations in first-line setting. Clinical trial information: NCT02060188. [Table: see text]

553 Background: Nivolumab (NIVO) provided durable responses (investigator-assessed [INV] ORR, 31%) and disease control (DCR, 69%) in pretreated pts with dMMR/MSI-H mCRC in CheckMate-142 (NCT02060188; Overman et al Lancet Oncol 2017). An interim analysis of the NIVO + ipilimumab (IPI) combination cohort of CheckMate-142 reported a preliminary ORR of 55% and manageable safety profile in a subset of pts (n = 84) with dMMR/MSI-H mCRC and ≥ 6 mo of follow-up (André et al ASCO 2017). Here we report for the first time efficacy and safety from the complete population (N = 119) of the NIVO + IPI cohort of CheckMate-142, which is the largest single-study report of an immunotherapy regimen in pts with dMMR/MSI-H mCRC. Methods: Pts with dMMR/MSI-H mCRC received NIVO 3 mg/kg + IPI 1 mg/kg Q3W for 4 doses followed by NIVO 3 mg/kg Q2W. Primary endpoint was ORR (INV; RECIST 1.1). Other endpoints were DOR, PFS, OS, and safety/tolerability. Results: Of 119 treated pts, 76% had ≥ 2 prior lines of therapy. Median follow-up was 13.4 mo. The ORR was 55% and DCR was 80% (Table). Notably, ORR in pts with a BRAF mutation was 55%. Among all responders, median DOR was not reached (NR), with 94% of responses ongoing at data cutoff. Tumor burden was reduced from baseline in 77% of pts. The 9-mo PFS and OS rates were 76% and 87%, respectively. Gr 3–4 TRAEs occurred in 32% of pts; 13% (any gr) and 10% (gr 3–4) of pts had TRAEs that led to discontinuation. No treatment-related deaths were reported. Results including a similar follow-up of the NIVO arm will also be presented. Conclusions: In the largest cohort of dMMR/MSI-H pts treated with an immunotherapy regimen, NIVO + IPI built on the efficacy reported with NIVO monotherapy, demonstrating enhanced clinical benefit and manageable safety, and may represent a new standard of care in pts with dMMR/MSI-H mCRC. Clinical trial information: NCT02060188. [Table: see text]

3531 Background: Nivo, a fully human anti-PD-1 mAb, provided an ORR of 31%, durable responses (median DOR not reached), and a 12-mo OS rate of 73.8% in pts with dMMR/MSI-H mCRC (Overman M, et al. 2017). Preliminary analysis of nivo + ipi, a humanized anti-CTLA-4 mAb, demonstrated manageable safety and promising efficacy in pts with dMMR/MSI-H mCRC (Overman M, et al . 2016). Here we report interim safety and efficacy of nivo + ipi in this pt population from the Checkmate 142 study (NCT02060188). Methods: Pts with dMMR/MSI-H mCRC who progressed on or were intolerant of ≥1 prior line of therapy received nivo 3 mg/kg + ipi 1 mg/kg q3w × 4 doses followed by nivo 3 mg/kg q2w until discontinuation due to disease progression or other reason. Primary endpoint was investigator-reported ORR by RECIST 1.1. Other endpoints included DOR, PFS, OS, safety, and tolerability. Results: 27 pts with dMMR/MSI-H mCRC treated with nivo + ipi received the first dose ≥6 mo prior to the database lock (DBL; Sept 2016). Of these pts, 93% received ≥2 prior lines of therapy. At the time of DBL, 44% of pts remained on treatment, and 14 pts had discontinued therapy due to disease progression (n=8) or TRAEs (n=6). ORR was 41% and disease control rate (DCR) was 78% (Table). The median time to response was 2.7 mo, and 82% of responses (9/11) were ongoing at 6 mo. The medians for DOR, PFS and OS had not been reached. Grade 3–4 TRAEs occurred in 10 pts (37%).TRAEs leading to discontinuation included acute kidney injury, increased transaminases, necrotizing myositis, sarcoidosis, dyspnea, and thrombocytopenia (1 each). No deaths were attributed to therapy. Conclusions: Initial analysis ofnivo + ipi in pts with ≥6-mo follow-up demonstrated a manageable safety profile and clinical activity characterized by a high DCR and encouraging survival benefit. This study is ongoing, and updated efficacy and biomarker analyses of ≈80 pts with ≥6-mo follow-up will be presented. Clinical trial information: NCT02060188. [Table: see text]

Background: MMR or MSI testing is recommended for mCRC pts and is often done locally by IHC or PCR testing, respectively (NCCN V1.2017) Nivo, a fully human anti-PD-1 mAb, demonstrated durable responses and a 12-mo OS rate of 73.8% in pts with mCRC locally assessed for dMMR/MSI-H status in the CheckMate 142 study (NCT02060188; Overman M, et al. 2017). Here we describe the results of local and central testing with respect to MMR/MSI status and clinical outcomes in the CheckMate 142 study. Methods: MMR/MSI status was assessed locally on archival tumor using IHC/PCR at screening and confirmed centrally by PCR (modified Bethesda panel) testing of tumor biopsy at enrollment. dMMR was defined by IHC as a loss of expression in ≥1 mismatch repair proteins. Stable microsatellite (MSS), low MSI (MSI-L), and high MSI (MSI-H), were defined as instability in 0, 1, or ≥2 markers, respectively. Pts with dMMR/MSI-H mCRC who progressed on or were intolerant of ≥1 prior line of therapy received nivo 3 mg/kg Q2W. Results: 74 ptswere dMMR/MSI-H by local testing. Of these pts, 53 (72%) were centrally confirmed as MSI-H, 7 pts had insufficient tissue sample for PCR testing, and 14 pts had a central test that did not match local test results. Of the 14 pts, 3 pts with a clinical history of LS were identified locally as dMMR but centrally as MSS (Table). INV-reported ORR was 31.1% in 74 pts locally determined as dMMR/MSI-H, 35.8% in 53 pts locally and centrally confirmed as MSI-H, and 21.4% in 14 pts not centrally confirmed as MSI-H. Conclusions: The similar clinical activity between pts locally confirmed as MSI-H and pts who were centrally confirmed as MSI-H suggest local testing is appropriate for identifying the dMMR/MSI-H pts who may benefit from nivo monotherapy. Clinical trial information: NCT02060188. Pt Local Testing Central Testing Clinical History of LS Method Result 1 IHC dMMR MSS NA 2 IHC dMMR MSS No 3 IHC dMMR MSS Yes 4 IHC dMMR MSS Yes 5 IHC/PCR dMMR (IHC)/MSI-H (PCR) MSS NA 6 IHC dMMR MSS Yes 7 IHC dMMR MSS No8 PCR MSI-H MSS NA 9 IHC/PCR dMMR (IHC)/MSI-H (PCR) MSS NA 10 IHC dMMR MSS No 11 IHC dMMR MSS NA 12 PCR MSI-H MSS NA 13 IHC dMMR MSI-L NA 14 IHC dMMR MSS NA NA = not available.

11569 Background: No validated prognostic biomarker is currently available for mCRC. This trial assessed cfDNA and MTV before treatment with regorafenib as prognostic biomarkers for progression-free survival (PFS) and overall survival (OS) in mCRC. Methods: After signed informed consent, mCRC patients were enrolled in a prospective non-randomized trial aiming to define unlikelihood to benefit from regorafenib (EudraCT number: 2012-005655-16) and assessed for cfDNA and FDG PET/CT MTV at baseline. cfDNA was extracted from 3mL of plasma and quantified using the Qubit 2.0 fluorometer. All target lesions were delineated on FDG PET/CT using a PERCIST-based threshold and their volumes were summed to obtain total MTV. MTV and cfDNA optimal cutoffs for OS and PFS prediction were determined by the Contal and O’Quigley’s method. MTV, cfDNA, age, gender, Body Mass Index (low, normal, high, obese), ECOG PS, number of chemotherapy lines (NCL), previous use of bevacizumab and presence of a KRAS mutation were included in a multivariate analysis. Results: MTV and cfDNA of 132 evaluable/141 eligible patients were well correlated (Spearman’s correlation coefficient = 0.70; p < 0.001) and risk groups for both PFS and OS were identified on the basis of cfDNA (cfDNA < 1 µg/mL; cfDNA≥1 µg/mL) and MTV (MTV < 100 cm³; 100-300 cm³; > 300 cm³). The multivariate analysis retained cfDNA, MTV, NCL, and obesity as independent parameters for PFS prediction, and cfDNA, MTV, NCL, BMI, and previous use of bevacizumab as independent parameters for OS prediction. Prognostic scores for PFS and OS were developed based on regression coefficients from the final Cox proportional hazards models. Prognostic scores for PFS (1.8 vs 5.3 months, HR: 3.15 for score ≥-3 vs < -3, (95% CI, 2.08-4.76); p < 0.001) and for OS (4.2 vs 13.9 months, HR: 4.59 for score ≥-6 vs < -6: (95% CI, 2.92-7.21); p < 0.001) both identified patients with much contrasted outcomes. Conclusions: Baseline cfDNA and MTV along with BMI parameters predict outcome in patients with mCRC before regorafenib onset. These parameters not related to treatment should be considered, if validated in further studies, as stratification factors in future clinical trials. Clinical trial information: 2012-005655-16.