Anti-PD-1 therapy in advanced sarcomas: is cutaneous primary site a stronger predictor of response than histologic subtype?

Abstract

Background Immune checkpoint inhibitors (ICIs) have shown modest antitumor activity in unselected advanced sarcomas. Histology driven approach to patient selection is the current standard for off-label anti-programmed cell death 1 (PD1) immunotherapy use. Methods We retrospectively reviewed the clinical characteristics and outcomes of patients with advanced sarcoma who were treated with off label anti-PD1 immunotherapy at our center. Results A total of 84 patients with 25 histological subtypes were included. Nineteen patients (23%) had a cutaneous primary tumor site. Eighteen patients (21%) were classified as having clinical benefit, including 1 patient with complete response, 14 with partial response, and 3 with stable disease lasting over 6 months with previously progressive disease. Cutaneous primary site location was associated with higher clinical benefit rate (58% vs. 11%, p < 0.001), longer median PFS (8.6 vs. 2.5 months, p = 0.003) and OS (19.0 vs. 9.2 months, p = 0.011), compared to non-cutaneous primary. Patients with histological subtypes that pembrolizumab is indicated per current National Comprehensive Cancer Network guidelines had modestly higher rate of clinical benefit versus other histologies, however, the difference was statistically insignificant (29% vs. 15%, p = 0.182) and no statistically significant difference in PFS or OS was observed between these groups. Immune-related adverse events were more frequently seen among patients with clinical benefit (72% vs. 35%, p = 0.007). Conclusions Anti-PD1-based immunotherapy is highly efficacious in advanced sarcomas of cutaneous primary site. Cutaneous primary site location is a stronger predictor of ICI response than histologic subtype and should be accounted for in treatment guidelines and clinical trial design.