Real-world immunotherapy outcomes in unresectable peritoneal mesothelioma: A French experience

Peritoneal mesothelioma is a rare disease treated with curative approach- cytoreductive surgery and hyperthermic intraperitoneal chemotherapy -when resectable.In case of inoperable disease or extra-peritoneal involvement, the standard of care is based primarily on systemic chemotherapy. Platinum-based chemotherapy is used in the first-line setting, but no standard exists for subsequent lines.Peritoneal mesothelioma harbors a pro-inflammatory tumor microenvironment, making it potentially sensitive to immune checkpoint inhibitors (ICIs).

We included inoperable patients with peritoneal mesothelioma treated between 2017 and 2024 at two institutions in France, using ICIs-based treatments (immunotherapy with or without anti-angiogenic agents).The primary endpoints were progression-free survival (PFS) and overall survival (OS).

A total of 22 patients with peritoneal mesothelioma were included.The median age at diagnosis was 57 years (IQR: 50-66);the majority had epithelioid histology (n = 17; 77 %).After a median follow-up of 13.76 months (95 % CI: 6.40-22.49),median Progression free survival(PFS) was 10.22 months (95 % CI: 4.82-15.87),median Overall Survival(OS) was 16.8 months (95 % CI: 6.46-37.73) No significant differences in PFS (p = 0.73) or OS (p = 0.16) were observed between BAP1-positive and BAP1-negative tumors.Among evaluable patients (n = 13, 62 %), the objective response rate was 30 % (95 % CI: 22 %-50 %).The disease control rate at 6 and 12 months for the entire cohort was:55 % (95 % CI: 33 %-74.5 %) at 6 months and 41 % (95 % CI: 21.9 %-63.04 %) at 12 months.Grade 3 toxicity occurred in 3 patients; no grade 4 toxicity was reported.

The benefit of ICI-based treatment was confirmed in this European real-world cohort and should be considered as a treatment option in this rare setting.