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PURPOSE Antitumor activity in preclinical models and a phase I study of patients with dedifferentiated liposarcoma (DD-LPS) was observed with selinexor. We evaluated the clinical benefit of selinexor in patients with previously treated DD-LPS whose sarcoma progressed on approved agents. METHODS SEAL was a phase II-III, multicenter, randomized, double-blind, placebo-controlled study. Patients age 12 years or older with advanced DD-LPS who had received two-five lines of therapy were randomly assigned (2:1) to selinexor (60 mg) or placebo twice weekly in 6-week cycles (crossover permitted). The primary end point was progression-free survival (PFS). Patients who received at least one dose of study treatment were included for safety analysis (ClinicalTrials.gov identifier: NCT02606461 ). RESULTS Two hundred eighty-five patients were enrolled (selinexor, n = 188; placebo, n = 97). PFS was significantly longer with selinexor versus placebo: hazard ratio (HR) 0.70 (95% CI, 0.52 to 0.95; one-sided P = .011; medians 2.8 v 2.1 months), as was time to next treatment: HR 0.50 (95% CI, 0.37 to 0.66; one-sided P < .0001; medians 5.8 v 3.2 months). With crossover, no difference was observed in overall survival. The most common treatment-emergent adverse events of any grade versus grade 3 or 4 with selinexor were nausea (151 [80.7%] v 11 [5.9]), decreased appetite (113 [60.4%] v 14 [7.5%]), and fatigue (96 [51.3%] v 12 [6.4%]). Four (2.1%) and three (3.1%) patients died in the selinexor and placebo arms, respectively. Exploratory RNA sequencing analysis identified that the absence of CALB1 expression was associated with longer PFS with selinexor compared with placebo (median 6.9 v 2.2 months; HR, 0.19; P = .001). CONCLUSION Patients with advanced, refractory DD-LPS showed improved PFS and time to next treatment with selinexor compared with placebo. Supportive care and dose reductions mitigated side effects of selinexor. Prospective validation of CALB1 expression as a predictive biomarker for selinexor in DD-LPS is warranted.

3012 Background: Ataxia telangiectasia and Rad3 related (ATR) is activated in response to replication stress from topoisomerase 1 inhibitors. Selective ATR inhibition with berzosertib potentiates the efficacy of irinotecan in colorectal mouse xenograft models. We hypothesized that berzosertib in combination with irinotecan is well tolerated, modulates the DNA damage repair response to irinotecan, and the combination is associated with clinical activity. Methods: This phase I study utilized a modified Storer’s up and down dose escalation design. Dose Levels (DLs) combined berzosertib 60 to 270 mg/m2 with irinotecan 180 mg/m2, every 2 weeks in a 4-week cycle. The primary endpoint was identification of the maximum tolerated dose (MTD) and recommended phase II dose (RP2D). Activity, pharmacokinetics (PK), and pharmacodynamics (PD) were secondary endpoints. The identification of molecular subpopulations sensitized to the combination was exploratory. Results: Between July 2016 and July 2021, 51 patients (pts) enrolled, of whom 50 received treatment. Pts most commonly had colorectal cancer (CRC, 39%), pancreatic cancer (24%), small cell lung cancer (SCLC, 6%) and non-small cell lung cancer (6%). The median number of prior lines of therapy was 4 (range, 2 to 11). In Stage I, 1 of 3 evaluable pts experienced dose-limiting toxicity (DLT) of grade 3 lung infection at DL3 (berzosertib 180 mg/m2 - irinotecan 180 mg/m2), and Stage II was initiated enrolling cohorts of 5 pts. In Stage II, 4 of the first 11 pts treated at DL4 (berzosertib 270 mg/m2 - irinotecan 180 mg/m2) were unable to complete the DLT evaluation period due to clinically significant toxicity not meeting DLT criteria: grade 2 diarrhea (1 pt), grade 3 diarrhea (1 pt), and grade 3 neutrophil decrease (2 pts). The protocol was amended to limit dose escalation beyond DL4. At DL4, 1 of 21 evaluable pts experienced DLT (grade 4 febrile neutropenia). Most common treatment-related grade ≥ 3 toxicities were neutrophil decrease (34%), lymphocyte decrease (30%), WBC decrease (28%), anemia (20%), diarrhea (16%), fatigue (8%) and hypokalemia (8%). 2 partial responses were observed, occurring in pts with pancreatic cancer and ATM alterations: 32% decrease in an ATM E11828/ATM K1109* tumor lasting 15.3 months and 68% decrease in an ATM R3008H/germline ATM R1882* tumor ongoing at 11 months. An additional pt with ATM S214fs*40 mutant colorectal cancer (CRC) experienced a 26% decrease lasting 7.5 months. Conclusions: Berzosertib 270 mg/m2 - irinotecan 180 mg/m2 was declared the RP2D. The combination is associated with manageable side effects and promising disease activity in ATM mutant solid tumors. PK and PD studies are in process. Tumor biopsy studies are planned in a 15 pt dose expansion cohort at DL4, enrolling pts with CRC, pancreatic cancer, SCLC and DNA damage repair deficient tumors. Clinical trial information: NCT02595931.

11581 Background: Desmoid tumors (DT) or aggressive fibromatosis are rare growths of fibroblastic connective tissue that can be locally aggressive but without metastatic potential. Most cases are sporadic, but 5-20% of cases are associated with Familial adenomatous polyposis (FAP). Despite numerous systemic options, optimal choice is unclear, and there is a paucity of studies comparing efficacy based on tumor site. Liposomal doxorubicin (LD) can be an appealing option for DT patients (pts) given its favorable schedule and toxicity profile. In this study, we compared outcomes in pts with intra-abdominal (IA) and extra-abdominal (EA) DT who received LD. Methods: We identified pts with DT who were treated with LD between 1/2010 - and 2/2022 at two sarcoma centers. Tumor and pt characteristics and outcomes were clinically (symptom improvement) and radiologically (RECIST 1.1) assessed. Results: 40 pts with DT treated with LD were identified; 58% female and 42% male. Pt characteristics and outcomes are summarized in Table 1. Primary tumor site was IA in 21 (53%) pts. FAP was present more commonly in pts with IA vs EA DT, 8/21 (43%) and 4/19 (21%), respectively. In the IA cohort, LD was given as first (15/21, 71%), second (10%) or third (19%) line therapy. LD was used more commonly as a later line in the EA cohort with 16%, 52%, 16%, and 16% receiving it in first, second, third, and fourth lines, respectively. 37 pts were evaluable for response. Response rate in the IA cohort treated in first-line was 50% (8 of 16) and 10 of 12 evaluable pts had symptomatic improvement. No first-line responses were seen in the EA cohort. As later lines of therapy, 7/12 pts had disease control in the second line, 6/8 pts in the third line, and 1/2 pts in the fourth line with LD in the IA cohort. 1 patient had fourth line response to LD in the EA cohort. Disease control rate with LD was 72.5% across all pts. Reasons for early discontinuation of LD included progression or lack of symptom improvement (20%), allergic reaction (12.5%), adverse effects (7.5%), or infection (2.5%). No acute or long-term cardiotoxicity was reported. 2 pts had no signs of recurrence or symptoms at follow-up, 33 pts were alive with symptomatic DT, 1 patient died from disease, and 3 were lost to follow-up. Conclusions: In our study, LD provided tumor response, disease control, and symptomatic improvement regardless of location or prior therapy, with responses most frequently seen in IA DT in first line setting. Further studies should include comparison of efficacy, adverse effects, and patient-reported outcomes while accounting for tumor location and line of therapy. [Table: see text]

TPS11595 Background: CCS of the soft tissues is a rare and aggressive subtype of sarcoma that often starts in the tendons of the arms or legs. It is molecularly characterized by t(12;22)(q13;q12) translocation, resulting in EWSR1-ATF1 or EWSR1-CREB1 gene fusion. Despite reports of occasional responses to systemic therapies, currently available therapies have shown limited efficacy in advanced CCS. Therefore, there is a significant unmet medical need for more active agents in CCS. Devimistat is a stable intermediate of a lipoate analog that inhibits pyruvate dehydrogenase and α-ketoglutarate dehydrogenase enzymes of the tricarboxylic acid (TCA) cycle preferentially within the mitochondria of cancer cells. Devimistat induces autophagy in cancer cells. In a metastatic mouse model of CCS, treatment with devimistat in combination with chloroquine significantly suppressed tumor growth (Egawa et al, 2018). Based on this data, we hypothesized that inhibition of autophagy with HCQ may sensitize cancer cells to devimistat with increased efficacy and acceptable toxicity. Given its expected synergy, we have initiated a single-arm phase I/II prospective, multicenter, open-label, non-randomized study to evaluate maximally tolerated dose (MTD), safety, and efficacy of devimistat in combination with HCQ in patients with R/R CCS. Methods: In the phase 1 portion of the study, patients with R/R CCS and other fusion-positive R/R sarcomas will be enrolled and a standard 3+3 design will be followed to evaluate toxicity, MTD, and recommended phase 2 dose. There will be two patient groups based on weight, and dose escalation will be conducted separately for each group. Starting dose of HCQ will be 5mg/kg PO BID for patients < 45 kg and 200 mg PO BID for patients ≥45 kg on days 1 through 5 of every 28 days. The first dose of HCQ each day will be followed 2 hours later by 1,000 mg/m2 devimistat (for patients < 45 kg) and 2,000 mg/m2 of devimistat (for patients ≥ 45 kg) administered over 2 hours. A maximum of 36 patients will be enrolled for the phase I portion, 18 for each patient group. In the phase 2 portion of the study, only relapsed or refractory CCS patients will be enrolled, and the response rate will be determined using RECIST 1.1. In phase 2, pharmacokinetics, duration of response, clinical benefit rate, progression-free survival, overall survival, safety, and patient-reported outcomes will also be assessed. This portion of the study will utilize Simon’s admissible two-stage design with 29 patients. This study started enrolling participants in November 2021 and has dosed six patients to date. The first two dose-escalation cohorts for patients ≥45 kg have been completed without DLT and the third dose level will be opening shortly. Clinical trial information: NCT04593758.

10511 Background: Sarcomas are rare and diverse malignancies with a subset developing in the context of heritable cancer predisposition syndromes. Data surrounding the frequency of inheritance and patient/genomic findings are limited. We aimed to describe the characteristics of patients with sarcoma referred for clinical genetic testing and to determine the prevalence of pathogenic/likely pathogenic germline variants (PGV/LPGV). Methods: We performed retrospective chart reviews of patients with sarcoma referred to Michigan Medicine Cancer Genetics Clinic between 12/2006 and 1/2020 and Vanderbilt Hereditary Cancer Clinic between 1/2005 and 1/2019. Reviewers obtained medical/family history, cancer phenotype, and results of germline genetic testing. Descriptive analyses were performed to assess the prevalence of germline variants classified as pathogenic/likely pathogenic according to American College of Medical Genetics criteria. Associations with clinical factors were tested for using Fisher’s exact test or Wilcoxon rank-sum test. Results: One-hundred sixteen patients with sarcoma underwent genetic evaluation during a 15-year period. Mean age at time of visit was 46 years (SD, 17.6 years; range, 1-80 years). Sixty-nine patients (59%) were female. The most common reasons for referral were personal history of multiple malignancies (n = 69, 59.4%), first degree relative (FDR) with malignancy (n = 67, 57.7%) and young age at diagnosis (age ≤ 18, n = 18, 15.5%). Forty-eight patients (41.4%) had both a history of multiple malignancies and a FDR with a malignancy. Eight patients had a FDR with sarcoma (6.9%). Of the 110 patients who underwent germline testing, 53 patients (48.2%) had a PGV/LPGV. Identified germline variants and frequencies are listed in the Table. There was no statistical significance between young age at diagnosis, history of personal malignancies, FDR with sarcoma, FDR with one or more malignancies, or multiple FDRs with malignancy and presence of a PGV/LPGV. Conclusions: In this multicenter study, approximately half of patients with sarcoma referred for cancer genetic testing had a PGV/LPGV associated with hereditary predisposition to cancer. There was no identified positive predictive factor for germline variants. Though TP53 was the most common, over 20 genetic variants were identified, supporting the consideration of multigene panel testing. Our study is limited to patients who were both referred to and attended genetic evaluation. Yet, the high frequency of pathogenic germline variants observed highlights the necessity for further investigation of the prevalence of and predictive factors for germline mutations in all sarcoma patients. Identified germline variants. [Table: see text]

e23500 Background: Sarcomas are a rare and heterogenous group of malignancies comprised of > 150 histologic subtypes. Adamantinoma-like Ewing sarcoma (ALES) is a rare, small round blue cell tumor that represents a variant of Ewing sarcoma (EWS). First described 20 years ago, ALES harbors a EWS subset defining EWS-related translocation; however, ALES has a complex epithelial differentiation component defining it as a distinct clinical entity. Most ALES cases arise in the head and neck, but it has also been reported in the extremities and thorax. Given the rarity of ALES, there is a paucity of literature to guide treatment and describe outcomes. Methods: We performed a retrospective review (January 1, 2010-January 1, 2022) at two sarcoma centers in the United States and identified 4 cases of ALES. Tumor and patient characteristics were described, and patient outcomes were assessed. Results: Four patients were identified. 3 (75%) were male. Median age at diagnosis was 37 years (range 23-57). Primary site of ALES was head and neck (50%) and thorax (50%). Median tumor size was 4 cm (2.7-5.5 cm). All patients underwent resection of their primary tumor, and two (50%)received adjuvant radiation therapy. All pts received/are receiving adjuvant chemotherapy. 75% of patients were treated with Vincristine, Doxorubicin, and Cyclophosphane (VDC) alternating with Ifosfamide & Etoposide (IE) for 12-14 cycles. One patient received 4 cycles of adjuvant carboplatin and etoposide and radiation after an initial diagnosis of basaloid carcinoma but recurred 47 months later and diagnosed at ALES at that time. That patient underwent re-resection followed by adjuvant chemotherapy with Vincristine, Doxorubicin, and Ifosfamide (VAI). Median follow-up from initial diagnosis was 25 months (3-39 months). All patients are alive with no evidence of disease. Conclusions: Similar to treatment of EWS, a multidisciplinary strategy is paramount. VDC/IE is a reasonable treatment strategy. Further multicenter collaboration is essential to define clinical characterization of this rare sarcoma subtype and to guide treatment particularly in the relapsed or refractory setting.[Table: see text]

e23562 Background: Ifosfamide, an alkylating agent used commonly in both hematologic and solid tumor malignancies, carries a notable risk for neurotoxicity/encephalopathy. Ifosfamide is available as both a reconstituted powder formulation and a solution for injection. Literature has shown that there may be higher rates of ifosfamide neurotoxicity/encephalopathy (INT/E) with the solution compared to the reconstituted powder. The primary objective of this study was to compare the rates of neurotoxicity/encephalopathy in association with the two available pharmaceutical formulations of ifosfamide. Methods: We performed a retrospective study of adult patients receiving at least one dose of either available pharmaceutical formulation of ifosfamide. The primary outcome was the incidence of formulation-associated INT/E. Secondary outcomes included additional risk factors for development of INT/E. Results: Of 218 patients evaluated, 212 were included in the study with 56 patients receiving the reconstituted powder formulation and 156 patients receiving the solution for injection formulation of ifosfamide. Baseline characteristics were similar between the two groups, including dose of ifosfamide received, use of INT/E prophylaxis, and renal and hepatic function. INT/E occurred in 4 patients (7.1%) receiving the reconstituted powder formulation vs 32 patients (20.5%) receiving the solution for injection (p = 0.022) Evaluation and analysis of additional risk factors for development of INT/E are ongoing, including the impact of baseline demographics, ifosfamide dosing, renal and hepatic function, and concomitant medications. Conclusions: In this study, hematology/oncology patients who were treated with ifosfamide had significantly lower rates of INT/E with the reconstituted powder formulation compared to the solution for injection. Further analysis regarding additional risk factors for INT/E development is ongoing.[Table: see text]

11528 Background: Chondrosarcoma is one of the most common bone malignancies in adults, and the third most common in pediatric patients (pts). The most prevalent subtype, conventional chondrosarcoma, is a slow growing tumor that is historically known to be refractory to chemotherapy. Anecdotal reports indicated a role for anti-PD-(L)1 in the treatment of this disease. This is the first prospective report on the efficacy of the PD-L1-targeting agent, atezolizumab, in this rare disease. Methods: Patients (pts) ages 2 and older with unresectable grade 2 or 3 conventional chondrosarcoma were eligible. No prior anti-PD-(L)1 treatment was allowed, otherwise pts were eligible irrespective of prior therapies as long as protocol-specified washout period requirements were met. Pts received atezolizumab 1200 mg (15 mg/kg with 1200 mg cap in pediatric pts) once every 21 days. Imaging was carried out at end of cycle 3, and then every two cycles. Research biopsies were collected from adult pts prior to C1D1, prior to C3D1, and at progression. Immuno-pharmacodynamic (IO-PD) studies were performed on paired tumor samples and circulating immune cells to help elucidate signaling pathways mediating the immune response, with focus on subsets of effector cells in the tumor microenvironment. Results: A total of 9 pts (7 males, 2 females) were enrolled in 6 centers across the US and Canada. Six pts were Caucasian/White, 1 Asian, 1 Hispanic, and 1 unknown. Median age was 49 years (42-72). No objective responses were seen. Three pts (33%) experienced disease stability (SD) per RECIST 1.1, for a median duration of 21 weeks as of data cutoff (January 2022). A patient with SD remains on active treatment (tx) for 35 weeks. Three patients had no tx-related adverse events (AEs). Six pts (67%) experienced at least one tx-related AE. Two patients experienced > G2 AEs, but only one was considered tx-related (lymphopenia). Immune-related AEs were all G1/2 and included hepatitis (2), hypothyroidism (1), hyperthyroidism (1), and maculopapular rash (1). IO-PD studies are ongoing and will be reported at the conference if available. Conclusions: Atezolizumab was well-tolerated but demonstrated limited activity in this cohort of pts with few treatment options. Ongoing IO-PD studies will provide insight into atezolizumab’s effect upon immune cell content and activation in the tumor microenvironment that will help design future immunotherapy trials in this disease and other sarcoma types. The study was funded by NCI Contract HHSN261201500003I. Clinical trial information: NCT04458922.

578 Background: GSK-3β overexpression is associated with worse prognosis and chemotherapy resistance in PDAC. GSK-3β inhibition reverses chemotherapy-resistance by inhibiting chemotherapy-induced, ATR-mediated, DNA damage response. 9-ING-41 has significant anti-tumor activity through apoptosis induction, anti-fibrotic activity and NK/T-cell effector stimulation. We hypothesized that 9-ING-41 in combination with GnP chemotherapy would lead to anti-tumor activity, with improved tumor responses in patients with advanced PDAC in the first line setting. Methods: Primary endpoint is disease control rate (DCR). DCR = confirmed complete response (CR), partial response (PR), or stable disease (SD) ≥ 16 weeks (wks). Secondary endpoints are safety and ORR (overall response rates). Eligibility: Advanced PDAC, ECOG PS 0-2, no prior therapy in the metastatic setting and no systemic therapy in prior 6 months. Pts received 9-ING-41 15mg/kg IV twice-weekly with G 1,000 mg/m2 and nP 125 mg/m2 on days 1,8,15 of a 28-day cycle. Simon 2-Stage Design for DCR of 65% and null hypothesis of 50% (historical control), 80% power and 2 sided-significance level of.05. Up to 23 fully evaluable pts planned for stage 1 and if ≥ 12 evaluable patients achieve a DCR 37 additional pts will be enrolled on a second stage or a randomized study commenced. Results: As of Sept 27, 2021, 42 pts enrolled. Median age: 67. 24 females, 18 males. 38 pts with metastatic and 4 with locally advanced disease. Prior adjuvant therapy: 4 pts each FOLFIRINOX and gemcitabine-based. No 9-ING-41-attributable SAEs to date. 9-ING-41 attributed AEs: visual disturbance: 24 (75%) G1/2, 1 (3%) G3; infusion reactions 9 (28%) G1/2. Chemotherapy-related AEs: anemia 13 (40%) G1/2, 1 (3%) G3; neutropenia 2 (6%) G1/2, 13 (40%) G3/4; thrombocytopenia 9 (28%) G1/2, 2 (6%) G3/4; diarrhea 8 (25%) G1/2, 4 (13%) G3; fatigue 9 (28%) G1/2, 3 (9%) G3; nausea/vomiting 24 (75%) G1/2, 1 (3%) G3; constipation 9 (28%) G1/2; febrile neutropenia 5 (16%) G3/4. In 21 pts currently evaluable for response, DCR was 62% and ORR 43%. There were 2 confirmed CRs, 6 confirmed and 1 unconfirmed PRs, 4 SD and 8 disease progressions were observed. Amongst responder’s median duration of response has not yet been reached. Conclusions: 9-ING-41 plus GnP demonstrated encouraging clinical activity but chemotherapy-related AEs were significant. Based on efficacy data to date, including confirmed CRs, we have commenced a randomized phase 2 study, evaluating 9-ING-41 plus GnP vs Gn P alone. Enrollment to the randomized study is now open (NCT03678883). Clinical trial information: NCT03678883.

11523 Background: Sarcoma pts often receive aggressive, highly immunosuppressive therapy and may be at high risk for severe COVID-19. Demographics, outcomes and risk factors for pts with sarcoma and COVID-19 are unknown. We aimed to describe the course of COVID-19 in sarcoma pts and to identify factors associated with adverse outcomes. Methods: The COVID-19 and Cancer Consortium (NCT04354701) is an international registry of pts with cancer and COVID-19. Adult pts (≥18 years old) with a diagnosis of sarcoma and laboratory confirmed SARS-CoV-2 were included from 50 participating institutions. Data including demographics, sarcoma diagnosis and treatment, and course of COVID-19 infection were analyzed. Primary outcome was the composite rate of hospitalization or death at 30 days from COVID-19 diagnosis. Secondary outcomes were 30 day all-cause mortality, rate of hospitalization, O2 need, and ICU admission. Descriptive statistics and univariate Fisher tests are reported. Results: From March 17, 2020 to February 6, 2021, N=204 pts were included. Median follow up was 42 days. Median age was 58 years (IQR 43-67). 97 (48%) were male. 30 (15%) had ECOG performance status ≥2. 104 (51%) received cancer treatment, including surgery or radiation, within 3 months of COVID-19 diagnosis. 153 (75%) had active cancer, of whom 34 (22%) had lung metastases. 100 (49%) pts met the composite primary endpoint; 96 (47%) were hospitalized and 18 (9%) died within 30 days from COVID-19 diagnosis. 64 (31%) required oxygen, and 16 (8%) required ICU admission. Primary endpoint rates were similar for pts who received cytotoxic chemotherapy (38/58, 66%) or targeted therapy (16/28, 57%). Pts with higher rates of the primary endpoint included patients ≥60 years old (59% vs 40%, OR 2.04, 95% CI 1.12-3.74, p=0.016), pts with ECOG PS ≥2 vs 0-1 (90% vs 41%, OR 12.2, 95% CI 3.44-66.8, p

11559 Background: The feasibility and utility of wearable devices is unknown in sarcoma patients (pts). Objective assessment of activity level, body composition, and PROs facilitate understanding of the tolerability and toxicity of cancer treatment. Methods: From 6/11-10/12/2020, we enrolled sarcoma pts receiving systemic therapy to a prospective study evaluating activity levels and sleep via a Fitbit Charge 3, body composition with the Inbody 570, and PROs using NIH PROMIS short forms (fatigue, pain, physical function, and sleep disturbance), the Generalized Anxiety Disorder Scale, and the Patient Health Questionnaire Depression Scale. Time on study was 12-16 weeks depending upon treatment. The Fitbit was worn continuously. Body composition and PROs were assessed every 3-4 weeks. Feasibility was defined as successful device wearing and data syncing. Data was collected through a cloud-based application, Fitabase. Results: 22 pts were approached and enrolled. Two pts did not complete the first study assessment due to disease progression and were excluded from analysis. 50% of pts were female. 90% of pts were white. Median age was 47 yrs (range 20-81). The most common histologies were Ewing sarcoma and leiomyosarcoma. 89.5% (17/19) of pts wore the Fibit for >3 weeks; median time was 68 days (5-112). 95% (19/20) of pts were able to sync data. Median step count was 2614 steps (376-19806). High step counts, defined as greater than the median, were associated with improved sleep (p=0.14) and physical function (p=0.22), and decreased pain (p=0.15), but these associations were not statistically significant. Low step counts, defined as lower than the median, were associated with skeletal muscle mass loss (p=0.22), but this was not statistically significant. Conclusions: Incorporating a fitness tracker is feasible in sarcoma pts receiving systemic therapy. It provides longitudinal, objective evaluation of activity levels and sleep patterns. Correlation of activity level with sleep, body composition, and PROs was limited due to small numbers; however, a larger prospective pilot study is ongoing.[Table: see text]

11503 Background: EHE is a rare vascular cancer arising in liver, lung, soft tissue and bone. The natural history of metastatic disease varies considerably from indolent growth over years to rapid growth with fatal outcome in months. Treatment of patients (pts) with metastatic EHE with antiangiogenic therapy induces tumor response in a minority of pts, and median PFS is 6-12 months. TAZ-CAMTA1 translocation results in activation of MAPK pathway and is an oncogenic driver in EHE. We sought to evaluate the effect of MEK inhibition using trametinib in pts with unresectable EHE. Methods: A phase 2 trial of trametinib 2 mg daily was conducted in pts with EHE though the Experimental Therapeutics Clinical Trials Network supported by NCI in collaboration with SARC. Additional support was provided by the EHE Rare Cancer Charity and the EHE Foundation. Pts had to have evidence of objective tumor progression or EHE-related pain requiring narcotics for relief prior to enrollment. Presence of TAZ-CAMTA1 translocation was analyzed by fusion-FISH after enrollment. Primary trial endpoint was objective response rate (ORR) per RECIST1.1 with at least 1 objective response required in the 1st 13 pts to expand enrollment to 27. The trial was amended after stage 1 to continue enrollment to 27 pts with TAZ-CAMTA1 detected by FISH with goal of >4 objective responses in this group. Secondary objectives were PFS and OS rates, safety and change in pt-reported global health and pain scores per PROMIS questionnaires. Results: 43 pts were enrolled between 6/2017 – 9/2020 across 10 sites and 41 started therapy. TAZ-CAMTA1 fusion was detected in 26, not detected in 7, test failed in 5 and was not performed due to insufficient tumor in 5. Median pt age was 54 (range 22-81 yrs) and 11 were >65 yrs; 25 were female; ECOG was 0 in 23, 1 in 16 and 2 in 3 pts. Most pts experienced reduction in tumor size. ORR per RECIST was 7% (3/41); in pts with TAZ-CAMTA1 detected, the ORR was 0% (0/26). Mean pain intensity and interference scores had a statistically significant improvement and global quality of life scores did not statistically change after 4 weeks of therapy. 17 pts remained on treatment > 6 months and 7 > 12 months. 25 pts stopped trametinib due to EHE progression, 6 died during treatment, 6 withdrew from treatment, 3 stopped drug due to adverse event and 1 is on treatment. The most common AEs related to trametinib were rash, fatigue, nausea/vomiting, diarrhea, alopecia and edema; Grade >3 AEs included anemia, dyspnea, hypoxia, hypotension, syncope and dermatitis. Conclusions: To our knowledge, this is the largest prospective clinical study focused on pts with EHE. Although the trial did not meet the ORR goal, stable disease > 6 months was seen in 40% of pts, and EHE-related pain improved on treatment. Trametinib was associated with expected cutaneous and GI adverse effects. Additional pt-reported outcomes and biomarkers of inflammation are undergoing analysis. Clinical trial information: NCT03148275.

9516 Background: Obesity is associated with improved outcomes in melanoma patients (pts) treated with PD-1, whereas low muscle mass, known as sarcopenia, has been associated with poor outcomes in many cancers. We sought to assess the impact of body composition on PD-1 outcomes. Methods: We analyzed pre-treatment CT scans at the L3 slice using Slice-o-matic software (Tomovision V. 5.0) to determine skeletal muscle, visceral adipose, and subcutaneous adipose tissue parameters for 104 pts with metastatic melanoma who received PD-1 monotherapy. We assessed sarcopenia using skeletal muscle index (SMI=skeletal muscle area/m2). We also quantified total adipose tissue index (TATI), and skeletal muscle gauge (SMG = SMI x skeletal muscle density [SMD]). We stratified pts into high/low groups using previously published cutoffs and assessed toxicity (tox), progression-free and overall survival (PFS/OS), and response rate (RR) by group. Results: Sarcopenia (low SMI) was negatively associated with any tox (39% vs. 60%, p=0.04) but not OS, PFS, or RR. Adiposity (TATI) was not associated with outcomes. By contrast, SMG was significantly associated with OS (median 35.5 vs. 16.0m, p=0.01 for high vs. low SMG). Interestingly, when incorporating TATI with SMG, we found that high SMG/high TATI pts (high muscle/high fat) have superior clinical outcomes (Table). Notably, low SMG/high TATI pts (low muscle/high fat) had seemingly the worst outcomes. Conclusions: We found that high SMG, a measure incorporating muscle area and density, was associated with improved OS in PD1 treated pts. Further, pts with high adiposity and high SMG had superior outcomes, potentially identifying the population responsible for the favorable effect of obesity in these pts. Validation and combination treated cohorts will be presented. [Table: see text]

11028 Background: DDCS is a rare bone tumor with a poor prognosis. While no standard therapy exists, NCCN guidelines recommend osteosarcoma regimens (ORs). Methods: We performed a retrospective review (January 1, 2007-June 1, 2018) at three sarcoma centers and identified 46 patients (pts) with DDCS to evaluate treatments and outcomes. Results: Median age was 62.5 years (23-83); 61% were male. Median tumor size was 10.5cm (2-34). Most pts had localized disease at diagnosis (dx) (80%), extremity primary (76%), and did not receive neo/adjuvant chemotherapy (70%) or radiotherapy (69%). Local and distant recurrences were frequent (35% and 57%, respectively) and rapid (6.6 months (m) and 5.4 m, respectively). Twenty-eight pts received chemotherapy, 9 neo/adjuvant and 19 for metastasis (met) (Table). Response rate to first line ORs was poor (53% progressed). Notably, 11% had a partial response (D/I). Tyrosine kinase inhibitors (TKIs) and immune checkpoint inhibitors (ICIs) led to stable disease. Median overall survival was 22.8 m and 7.2 m; 5-year survival rates were 30% and 0% in localized and metastatic disease, respectively. Median follow-up was 12.5 m (1.4-120). A multivariate cox proportional hazards model (age, sex, location, met at dx) identified met at dx as the only risk factor for worse prognosis (HR 2.8, p=0.026). Conclusions: DDCS is an aggressive malignancy with a poor prognosis. Despite guidelines to treat with ORs, the benefit is unclear, illustrating the need for randomized trials comparing standard regimens to novel agents. [Table: see text]

e21005 Background: HD IL2 treatment (Tx) produces durable complete responses (CRs) and surgical CRs. Patients (pts) achieving partial response (PR) and stable disease (SD) demonstrate improved survival compared with pts who progress. Methods: 7 HD IL2 Tx centers identified pts with survival > 5 years (yrs) after HD IL2. DFS was from end of IL2 to January 2017. Tx courses generally consisted of 2 1-week cycles of HD IL2, 600,000-720,000 U/kg IV every 8 hours. We collected data on pts Tx with HD IL2 alone, or HD IL2 plus local Tx (surgery or radiation (SRS) leading to CR) with survival > 5 yrs after HD IL2 Tx. Results: 72 pts are reported: 29 RCC (male 22, female 7) and 43 mm (male 26, female 17). Median age at Tx of RCC is 54 yrs (range, 47-67 yrs) and of mm is 50 yrs (range, 24-72 yrs). Sites of metastatic disease for 26 mm pts were lymph nodes (LN) -18, lungs-12, bone-6, liver-9, brain-3, other organs-10 and for 22 RCC pts were lung-17, LN-5, adrenal-4, bone-3, other organs-8. Number of IL2 courses received: 1-10 pts, 1.5-4 pts, 2-28 pts, 2.5-5 pts, 3-24 pts, 4-one pt. Among the 29 RCC pts, there are 24 CRs, 3 surgical CRs and 2 PRs with no further Tx. Among 43 mm pts, there are 34 CRs, 2 near CRs, and 7 Surgical/SRS CRs. DFS in these pts after HD IL2 Tx ranges from 5+ yrs to 30+ yrs, median 10.5+ yrs. 10 RCC and 16 mm are alive > 5 - < 10 yrs after IL2, and 19 RCC and 27 mm are alive > 10 yrs after IL2. LT toxicity among these 72 pts includes hypothyroidism-5 pts, arthralgias/arthritis-5 pts, vitiligo-3 pts, and 1 pt each: neuropathy, PVCs, and normal pressure hydrocephalus. Additional pts may be added as records become available. Conclusions: We document LT DFS ( > 5 yrs) after CR or PR from HD IL2 alone. Surgical or SRS conversion of PR to CR can produce durable CRs. LT DFS was observed in pts with visceral and bone metastases, not only those with LN or lung sites. Neither age, sex, nor number of courses of IL2 predicted LT DFS. Chronic toxicity due to IL2 is uncommon in LT survivors.

e21000 Background: aPD1, alone or in combination with ipilimumab (IPI), produces durable responses in a subset of MM. Tumor features that correlate with treatment response, including size, number, and location of metastases (mets) are not well defined. Methods: We collected clinical data from mm pts treated at one center who received aPD1 (n = 185) or aPD1 + IPI (n = 42). We correlated number of mets, size of largest tumor, and organ involvement with response rate (RR), progression-free survival (PFS) and overall survival (OS). Results: Among all pts, RR was 67% for aPD1 + IPI and 41% for aPD1 alone. In univariate analyses, responders to aPD1 had lower diameter of largest tumor (4cm vs. 5.5cm; p = 0.02) whereas aPD1 + IPI had equivalent largest tumor diameters (p = 0.65). Regarding sites of mets, liver mets were associated with lower RR in aPD1 treated pts (26% vs. 46%), lower PFS (median 138 vs. 326 days, p = 0.02), and lower OS (median 334 vs. 1080 days, p < 0.01). No associations with RR, PFS, or OS were observed with liver mets in aPD1 + IPI treated pts. We also did not observe any differences between pts who did or did not have lung, lymph node, or brain mets for either aPD1 or aPD1 + IPI. Interestingly, superior RR to aPD1 + IPI was observed in pts with bone mets compared to those without bone mets (91% vs. 58%, p = 0.048). Regarding number of sites, RR to aPD1 was greater in pts with ≤10 mets compared with those with > 10 (46% vs. 28%, p = 0.02), although no consistent relationship was observed at lower cutoffs. In multivariable analyses, diameter of largest tumor (tumor bulk) was independently associated with PFS (OR, 1.11, p < 0.001) and OS (OR 1.08, p < 0.001) whereas AJCC stage, lactate dehydrogenase, liver mets, ECOG performance status, number of mets, and prior therapies were not significant. Tumor bulk and other risk factors were not associated with PFS or OS in aPD1 + IPI. Conclusions: Tumor bulk was strongly and independently associated with clinical outcomes in aPD1 but not IPI + aPD1. Other associations with disease sites (liver and bone) need further validation. In conjunction with molecular biomarkers, clinical predictors may help guide selection of aPD1 or aPD1 + IPI.

10551 Background: Treating STS with systemic therapy beyond six months is challenging due to cumulative toxicity. Trabectedin (T) has demonstrated efficacy and tolerability in STS and became availa...

10570 Background: In patients (pts) with localized soft tissue sarcoma (STS), 80% of relapses occur within the first 2 years (yrs) after definitive resection. However, relapse after 3 yrs is not un...

5034 Background: Prostate cancer has an excellent prognosis with a 10-year relative survival of 99.7%. The long survival for this common cancer raises questions about the risk of second primary mal...

10524 Background: Approximately 50% of pts with localized, >5 cm, high grade STS develop metastatic disease. Although controversial, adjuvant chemotherapy has demonstrated improved disease-free (DFS) and overall survival (OS). AI can cause significant toxicities that often lead to hospitalization. GT is active in metastatic STS pts and as compared to AI has a favorable schedule and toxicity profile. Methods: In a single-institution phase II study, pts with localized, resectable, high grade STS >5 cm were randomized to receive AI or GT. Pts were stratified by neo- or adjuvant treatment and extremity or non-extremity tumor. Pts received A (75 mg/m2 over 48 hrs) and I (2.5 g/m2/d on D1-3) or G (900 mg/m2 over 90 min on D1,8) and T (100 mg/m2 on D8), both arms with GCSF, for 4 cycles unless progression. Radiation was given after chemotherapy. The primary endpoint of the trial was hospitalization rate during chemotherapy and was compared using a chi square test and multiple logistic regression adjusting for other variables. The trial was powered to detect a reduction in hospitalization rate from 35% to 10% using GT. Survival functions were estimated using Kaplan-Meier method. Results: 84 pts were enrolled from 11/04-8/12 with 80 pts evaluable. The median age is 56 yrs (19-76) and tumor size is 7.8 cm (3.2-25). 55 pts received neoadjuvant therapy and 48 had extremity STS. In the AI arm, 13/37 (35%) pts were hospitalized vs. 11/43 (26%) in the GT arm (p=0.25). The most frequent reason for hospitalization in AI arm was febrile neutropenia (7 events) and in GT arm was hypersensitivity reaction (4 events). The median DFS of pts treated with AI vs GT is 24 months vs not reached, respectively; median follow up is 30 (1-87) months. The 2-year DFS rate is 53% (SD 9%) in the AI arm vs. 71% (SD 7%) in the GT arm and remains marginally significant after adjusting for age, gender, neoadjuvant therapy, tumor site and size (p=0.054). OS rates are not significantly different between arms. Conclusions: Hospitalization rate was not significantly lower with GT compared to AI, although toxicity profile was different. DFS but not OS is marginally improved with GT. Clinical trial information: NCT00189137.