Study Finds Pembrolizumab Delivers Clinical Benefit in Selected Histotypes of Rare Sarcoma

Findings presented at the European Society of Modern Oncology 2020 showed that 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).

The results from a cohort of patients with rare sarcomas in the phase 2 study, presented by professor Jean-Yves Blay, MD, 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. Further, the eligible patients were under 18 years of age with an ECOG performance less than 1 and advanced disease that was resistant to standard treatment.

Pembrolizumab was administered at 200 mg intravenously as a 30-minute infusion on day 1 of every 21-day cycle for a maximum of 2 years to all participants. Further, the primary endpoint of the study was the confirmed objective response rate, whereas secondary endpoints included clinical benefit rate, duration response, PFS, OS, and safety, according to the study authors.

Eighty patients with rare sarcomas were classified according to histotype into 5 groups: chordoma, alveolar soft-part sarcoma (ASPS), desmoplastic small round cell tumor (DSCRT), SMARCA4-malignant rhabdoid tumor (SMBT), and other histotypes.

Patients received a median of 5 cycles of pembrolizumab from July 2017 to February 2020. The efficacy analysis of the overall patient population showed the best response was partial response, which was observed in 13 patients, and stable disease was observed in 29 patients.

The 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. These responses included 50% observed in SMBT, 39% in ASPS, 17% in DSCRT, 8% in chordoma, and 6% showing responses in other histotypes, according to the study authors.

The response was also reflected in survival rates, with the median PFS at 5.7 months in chordoma, 14 months in ASPS, 5 months in DSCRCT, not reached in SMBT, and 2.7 months in the other histotypes group. At data cut-off, the 1-year PFS rates in the respective histotypes were 35%, 58%, 0, 62.5%, and 8%.

Additionally, the median OS was reached in 3 of the 5 groups, with the median OS at 20 months in the chordoma cohort, 7.4 months in DSCRT, 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% in the group with other histotypes.

Trial discontinuation after receiving a median of 4 cycles was reported for 54 patients, with death occurring in 28 patients after receiving a median of 3 cycles. Twenty-seven of these deaths were cancer-linked and 1 patient death was due to other causes, according to the study authors.

The researchers concluded that pembrolizumab shows high levels of prolonged activity in selected subtypes of rare sarcomas. Translational research to understand the determinants of response is ongoing, since these types of sarcomas are not consistently associated with programmed death-ligand 1 expression, high tumor mutational burden, cell infiltrates, or tertiary lymphoid structures.

REFERENCE

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. https://www.esmo.org/meetings/esmo-virtual-congress-2020/meeting-resources/scientific-news/pembrolizumab-delivers-clinical-benefit-in-selected-histotypes-of-rare-sarcoma. Presented September 20, 2020. Accessed September 23, 2020.