Treatment with pembrolizumab monotherapy provided responses in patients with rare sarcomas that varied by histotype, as did progression-free survival (PFS) and overall survival (OS), according to findings presented by Prof. Jean-Yves Blay of the Centre Léon Bérard in Lyon, France at the ESMO Virtual Congress 2020.
Prof. Blay presented first results from a cohort of patients with rare sarcomas in the phase II, non-randomised parallel arm, open-label, multicentre AcSé Pembrolizumab study, which investigated the efficacy and safety of single agent pembrolizumab in rare cancers.
The histotypes evaluated were all rare sarcomas with an incidence of less than 0.2 cases per 100,000 individuals per year. The eligible patients were aged >18 years, with ECOG performance status ≤1, and advanced disease that was resistant to standard treatment.
Pembrolizumab was administered at 200 mg i.v. as a 30-minute infusion on Day 1 of every 21-day cycle for a maximum of 2 years to all participants. The primary endpoint of the study was the confirmed objective response rate (ORR) according to RECIST v1.1. and secondary endpoints included clinical benefit rate (CBR), duration of response (DoR), PFS, OS and safety.
The 80 patients with rare sarcomas were classified according to histotype into 5 groups: chordoma (n=24), alveolar soft-part sarcoma (ASPS, n=13), desmoplastic small round cell tumour (DSRCT; n=6), smarca4-malignant rhabdoid tumour (SMBT; n=6) and other histotypes (n=31).
From July 2017 to February 2020, patients received a median of 5 cycles (range, 1 to 33) of pembrolizumab.
Efficacy analysis of the overall patient population showed the best response was partial response (PR), which was observed in 13 (16.25%) patients (95% confidence interval [CI] 8.9-26.2%) and stable disease (SD) in 29 (36.25%) patients.
Response was found to be histotype dependent, with the group of patients with SMBT faring the best and patients with other histotypes showing the lowest response rate; 3 (50%) responses were observed in SMBT, 5 (39%) in ASPS, 1 (17%) in DSCRCT, 2 (8%) in chordoma, and 2 (6%) showed response in other histotypes (p = 0.010).
Response was reflected in the survival rates; median PFS was 5.7 months in chordoma, 14 months in ASPS, 5 months in DSCRCT, not reached SMBT, and 2.7 months in the other histotypes group (p = 0.00016). At data cut-off, the 1-year PFS rates in the respective histotypes were 35%, 58%, 0, 62.5%, and 8%.
Median OS was reached in 3 of the 5 groups; median OS was 20 months in the chordoma cohort, in 7.4 months in DSRCT and 5.4 months in the other histotype group. The 1-year OS rates were 72% in chordoma, 90% in ASPS, 50% in DSCRCT, 83% in SMBT and 40% (p= 0.02) in the group with other histotypes.
Regarding the safety endpoint, trial discontinuation after receiving a median of 4 cycles was reported for 54 (67.5%) patients. Death occurred in 28 patients after receiving a median of 3 cycles; of these deaths, 27 were cancer-linked but due to other causes in one patient.
Prof. Blay and colleagues concluded that pembrolizumab shows high levels of prolonged activity in selected subtypes of rare sarcomas. These sarcomas are not consistently associated with PD-L1 expression, high TMB, cell infiltrates, or tertiary lymphoid structures. Translational research to understand the determinants of response is ongoing.
This UNICANCER study was funded by MSD.
1619O – Blay J-Y, Chevret S, Penel N, et al. High clinical benefit rates of single agent pembrolizumab in selected rare sarcoma histotypes: First results of the AcSé Pembrolizumab study. ESMO Virtual Congress 2020.