Background Immune checkpoint inhibitors (ICIs) represent an appealing treatment for patients with advanced urothelial cancer (aUC) and a poor performance status (PS). However, the benefit of ICIs for patients with a poor PS remains unknown. It was hypothesized that a poor Eastern Cooperative Oncology Group (ECOG) PS (≥2 vs 0‐1) would correlate with shorter overall survival (OS) in patients receiving ICIs. Methods In this retrospective cohort study, clinicopathologic, treatment, and outcome data were collected for patients with aUC who were treated with ICIs at 18 institutions (2013‐2019). The overall response rate (ORR) and OS were compared for patients with an ECOG PS of 0 to 1 and patients with an ECOG PS ≥ 2 at ICI initiation. The association between a new ICI in the last 30 and 90 days of life (DOL) and death location was also tested. Results Of the 519 patients treated with ICIs, 395 and 384 were included in OS and ORR analyses, respectively, with 26% and 24% having a PS ≥ 2. OS was higher in those with a PS of 0 to 1 than those with a PS ≥ 2 who were treated in the first line (median, 15.2 vs 7.2 months; hazard ratio [HR], 0.62; P = .01) but not in subsequent lines (median, 9.8 vs 8.2 months; HR, 0.78; P = .27). ORRs were similar for patients with a PS of 0 to 1 and patients with a PS ≥ 2 in both lines. Of the 288 patients who died, 10% and 32% started ICIs in the last 30 and 90 DOL, respectively. ICI initiation in the last 30 DOL was associated with increased odds of death in a hospital (odds ratio, 2.89; P = .04). Conclusions Despite comparable ORRs, ICIs may not overcome the negative prognostic role of a poor PS, particularly in the first‐line setting, and the initiation of ICIs in the last 30 DOL was associated with hospital death location.

7053 Background: Mutations in isocitrate dehydrogenase 1 ( IDH1) occur in ̃3% of patients (pts) with MDS and are associated with increased transformation to acute myeloid leukemia (AML). Ivosidenib (IVO), an oral, potent, targeted inhibitor of the mutant IDH1 (mIDH1) enzyme, is FDA approved for m IDH1 R/R AML and m IDH1 newly diagnosed AML in pts ≥75 years old or with comorbidities precluding the use of intensive induction chemotherapy. In the first-in-human study of IVO in pts with m IDH1 advanced hematologic malignancies (NCT02074839), 12 pts with R/R MDS received IVO 500 mg once daily (QD). Based on encouraging safety and efficacy findings, including an investigator-assessed overall response rate (ORR) of 75%, with median response duration of 21.4 months, the FDA granted Breakthrough Therapy designation to IVO in m IDH1 R/R MDS and the study was amended to enroll additional pts. We report updated results. Methods: This substudy of the single-arm, open-label study of IVO evaluated pts with R/R MDS after documented failure or relapse following prior standard therapy including intensive chemotherapy and hypomethylating agents. Other key eligibility criteria included: high disease burden based on IPSS or IPSS-R risk at baseline; an Eastern Cooperative Oncology Group performance status score of 0–2; and no prior IDH1 inhibitor therapy. Pts received IVO 500 mg QD orally on days 1–28 of 28-day cycles. Results: As of 08May2021, 16 pts with R/R MDS were enrolled: 5 (31%) pts remained on treatment and free from leukemic transformation; 11 (69%) had discontinued including 6 for disease progression, 1 for allogeneic stem cell transplantation, and 1 owing to an adverse event (AE) of sepsis (the only fatal AE; reported by investigator as not related to IVO). AEs are summarized in the Table. 2 pts each experienced differentiation syndrome (grade 2) and QTcF prolongation (grade 1 and 2). 7/16 pts achieved complete response (CR, 44%; 95% CI, 20%, 70%), 1 achieved partial response (6%), and 5 achieved marrow CR (31%), resulting in an ORR of 81% (95% CI, 54%, 96%). Hematologic improvement in ≥1 lineages was achieved by 11/16 (69%) pts. The Kaplan-Meier estimate of duration of CR+PR at 12 months was 60%. 3 pts experienced CRs lasting 24.0, 63.7, and 65.4 months, which remain ongoing. 5/7 pts (71%) who were transfusion dependent at baseline became independent of red blood cell or platelet transfusions for 56 or more consecutive days on treatment. Additional translational data are being analyzed. Conclusions: In pts with m IDH1 R/R MDS, IVO monotherapy was tolerable and induced durable remissions and transfusion independence. These findings support the role of IVO as an effective, oral, targeted treatment for pts with m IDH1 R/R MDS. Clinical trial information: NCT02074839. [Table: see text]

Background Gastrointestinal stromal tumor (GIST) is the most common primary mesenchymal neoplasm of the gastrointestinal tract. Mutations of KIT and platelet-derived growth factor receptor alpha have been well characterized in GISTs. Patients with KIT mutations are generally sensitive to treatment with tyrosine kinase inhibitors. However, some patients with GIST, while initially sensitive to TKIs, gain resistance in later stages of treatment. Heterologous rhabdomyomsarcomatous dedifferentiation of advanced GISTs after long-term imatinib mesylate (IM) therapy has been reported. In these cases, the underlying molecular mechanism of tumor progression and transformation is unclear. Case presentation We report one such patient with rhabdomyosarcomatous dedifferentiation of a GIST without metastatic disease after brief 3-month therapy with IM. The tumor was composed of two distinct phenotypes, a CD117 negative region with rhabdomyosarcomatous differentiation directly adjacent to a CD117 positive classic GIST region. Molecular analysis identified the activating KIT exon 11 mutation in both regions, indicating a common origin for both phenotypes. Additionally, the dedifferentiated component contained two synonymous variants in platelet-derived growth factor receptor alpha and KIT. The increased number of synonymous variants in the rhabdomyosarcomatous region may reflect increased genetic instability of this tumor that may have resulted in the loss of CD117 expression in the dedifferentiated component. Conclusion This study adds to the growing consensus that rhabdomyosarcomatous GIST progresses from a common GIST primary tumor. The role of IM in this progression is uncertain; however short duration of IM treatment in this study supports the hypothesis that rhabdomyosarcomatous GIST progression is not a consequence of IM therapy. Furthermore, we provide additional information supporting the observation that CD117 negative rhabdomyosarcomatous transformation maintains the activating KIT variant without KIT expression.

Background: Background: CPX-351 (Europe: Vyxeos ® liposomal; United States: Vyxeos ® ) is a dual-drug liposomal encapsulation of daunorubicin and cytarabine in a synergistic 1:5 molar ratio. CPX-351 is approved for newly diagnosed, therapyrelated acute myeloid leukemia (AML) or AML with myelodysplasia-related changes in adults in Europe and patients aged ≥1 year in the United States who are candidates for intensive chemotherapy (IC). However, the appropriate dosage of CPX-351 in patients unfit for IC may be different from the label dosage. Venetoclax (VEN; BCL-2 inhibitor) + low-dose cytarabine has demonstrated efficacy in unfit patients with AML, and drug synergism/additivity in preclinical studies provided a rationale for combining CPX-351 + VEN clinically. Aims:Aims: Our study evaluates the safety and efficacy of lower-intensity CPX-351 + VEN in adults with newly diagnosed AML who are unfit for IC. Methods:Methods: This is an ongoing, open-label, phase 1b study (NCT04038437). Patients who achieve at least partial remission after 1 or 2 cycles may receive up to 4 similar cycles in the dose-exploration phase (DEP) or up to 8 similar cycles in the expansion phase (EP). Patients are assessed for response (morphology, measurable residual disease [MRD]) and monitored for safety and survival. Results:Results: The data include 31 patients enrolled by 15 September 2021, with a data cutoff of 2 December 2021: 4 patients in the DEP at dose level 1 (CPX-351 20 units/m 2 on Days 1 and 3 + VEN 400 mg on Days 2 to 21 of each cycle), 7 patients in the DEP at dose level 2 (CPX-351 40 units/m 2 + VEN 400 mg), and a total of 20 patients in the DEP and EP at dose level 1b (CPX-351 30 units/m 2 + VEN 400 mg), which was established as the recommended phase 2 dose. Patients were considered unfit for IC based on age ≥75 years (n=15) or health (Eastern Cooperative Oncology Group performance status of 2 to 3 and/or comorbidities [n=16]). Median age was 74 years (range: 60, 90); 65% were male; 77% had de novo AML; 58% had poor-risk disease; and 23% had a TP53 mutation.Nonhematologic treatment-emergent adverse events (TEAEs) in ≥20% of patients were diarrhea (26%), cough (23%), dyspnea (23%), and nausea (23%). Hematologic grade ≥3 TEAEs were reported in 17 (55%) patients; no nonhematologic grade ≥3 TEAE was reported in >10% of patients. There were no deaths by Day 30; mortality at Day 60 was 13%, with deaths due to myocardial infarction unrelated to therapy (n=1), worsening lung infection (n=1), and disease progression (n=2). Median (interquartile range) recovery times were 30 days (22, 34.5) to neutrophils ≥500/μL and 21 days (21, 27) to platelets ≥50,000/μL. Complete remission (CR) or CR with incomplete neutrophil or platelet recovery (CRi) was achieved by 16/28 (57%) patients with an evaluable remission assessment. All 16 of these patients achieved remission (CR or CRi) after the first treatment cycle. MRD negativity was achieved by 12/16 (75%) patients with CR or CRi, primarily after Cycle 1 (Cycle 1: n=8; Cycle 2: n=2; Cycle 3: n=1;...

e19011 Background: Venetoclax (Ven) is a BCL-2 inhibitor approved in combination with hypomethylating agents (HMAs) in newly diagnosed AML patients who are not candidates for intensive induction based on impressive response rates (CR+CRi of 66.4%) and median overall survival (14.7 months) compared to HMA therapy alone (DiNardo CD, NEJM, 2020). Ven was also used in combination with 10 days of a HMA (Decitabine) in a phase II study. In the subgroup of patients with relapsed AML, some of which previously received HMA, the ORR, CR+CRi, and median OS were 62%, 42%, and 7.8 months respectively. (DiNardo CD, Lancet, 2020). To our knowledge there are no studies specifically looking at patients with AML receiving HMA + Ven with previous exposure to a HMA agent. Methods: We conducted a single center retrospective study of AML patients who received HMA + Ven therapy after previously receiving a HMA agent. Baseline demographic, clinical, laboratory, pathology, and outcomes data were collected by retrospective chart review. Response criteria was determined by 2017 ELN recommendations. Kaplan Meier was constructed to summarize time to event data. Results: A total of 17 patients were identified that met these criteria. 7 patients (41%) had progressed on prior HMA treatment, 11 patients (65%) received prior intensive chemotherapy, and 5 patients (29%) received previous Allogenic SCT prior to HMA+Ven therapy. 10 patients (59%) had either a TP53 mutation or 17p deletion and 11 patients (65%) had complex cytogenetics (≥ 3 cytogenetic abnormalities). Other patient characteristics are included in table below. For the entire cohort, the ORR (CR, CRi, PR) was 41% and the CR/CRi rate was 6%; The ORR in the following subgroups for previous HMA failure, TP53 mutation/17p deletion, and complex cytogenetics were 14%, 30%, and 36% respectively. The median Progression free survival and overall survival for the entire cohort was 2 months (1-4 months 95% CI) and 3 months (1-5 months, 95% CI) respectively. 15 patients (88%) were deceased and all deaths were attributed to AML (12/15) or infection (3/15). None of the patients went on to receive an Allogenic SCT. Conclusions: Although a limited sample size which includes many patients with a TP53/17p aberration, complex cytogenetics, Allogenic SCT relapse, and/or heavily pre-treated AML, this data describes poor outcomes in patients receiving HMA+Ven after previous HMA exposure. Patients with previous HMA failure in particular had a poor response rate. None of the patients received 10 day decitabine and it is unclear if this had any effect on the results. It would be beneficial to supplement this data with experience from multiple centers. Patient Characteristics (N = 17).[Table: see text]