(P 464) EFFICACY OUTCOMES AMONG PATIENTS WITH ADVANCED EPITHELIOID SARCOMAS OF PROXIMAL-TYPE AND DISTAL-TYPE TREATED WITH TAZ: POST HOC ANALYSIS OF STUDY EZH-202

Objective: To report efficacy outcomes of patients (pts) with proximal-type epithelioid sarcoma (pES) and distal-type ES (dES) treated with tazemetostat (TAZ) in the Phase 2 study EZH-202 (NCT02601950), a multicenter, open-label, single-arm basket trial with results reported so far only for a single cohort (cohort 5).

Methods: This post-hoc unplanned analysis of ES pts in EZH-202 (Pooled Cohorts 5 and 6) stratified pts by ES subtypes. Analyses were descriptive; confidence intervals (CIs) were calculated but no comparisons or statistical tests were performed.

Results: Among 124 patients with documented ES subtype, 69 (56%) had pES and 55 (44%) had dES. Median age and sex distribution were similar for pES and dES. Stage IV disease at diagnosis was more common among pES (61%) than dES (53%). Normal performance status (ECOG 0) was more common in dES (67%) than pES (58%). Most pts exhibited progressive disease prior to study entry (pES: 99%; dES: 95%). Pts with pES exhibited larger recorded tumor bulk (median RECIST v1.1 sum of target lesion diameters; 7.0 cm) than dES (4.4 cm).

Objective response rates (ORR) were similar among pES (16%, 95% CI: 9-27) and dES (13%, 95% CI: 6-25). Median progression-free survival (PFS) during TAZ was similar for both groups (pES: 4.0 months (mos), dES: 4.1 mos). Disease control rate (DCR) was similar between groups at 32 weeks (pES: 29%; dES: 25%). Median duration of response was not met for pES and 22 mos for dES. Receipt of subsequent anticancer therapy post-TAZ was similar among pES (49%) and dES (51%). Median overall survival (OS) was slightly higher for pES (25 mos) than dES (20 mos). For all differences described, 95% CIs overlapped, indicating that results were not statistically different.

Conclusion: Baseline pt characteristics prior to EZH-202 enrollment showed a more severe clinical presentation in pES compared to dES, as expected. TAZ demonstrated anticancer efficacy both in pts with pES and dES. Despite small differences in the magnitude of anticancer efficacy, no conclusions can be drawn given small patient numbers and overlapping 95% CIs.