Multicenter phase II trial of ipilimumab and nivolumab in metastatic or unresectable perivascular epithelioid cell tumor (PEComa): a substudy of Dual Anti-CTLA-4 and Anti-PD-1 blockade in Rare Tumors (DART) SWOG S1609 (Cohort 38).

BACKGROUND: Malignant perivascular epithelioid cell tumors (PEComas) are ultra-rare, aggressive mesenchymal neoplasms associated with poor outcomes. Standard-of-care systemic therapy includes mammalian target of rapamycin (mTOR) inhibition and chemotherapy. Immune checkpoint inhibition has not been previously studied in patients with advanced PEComas in a prospective clinical trial. METHODS: This is an open-label phase 2 trial of ipilimumab (1 mg/kg intravenously every 6 weeks) plus nivolumab (240 mg intravenously every 2 weeks) in rare tumors; here we report the cohort of patients with advanced malignant PEComa recruited from >1,000 sites across the USA. Primary end point was objective response rate, with progression-free survival, overall survival, and toxicity as secondary end points. RESULTS: 17 patients were enrolled (N=16 evaluable). Median age was 59.5 years (range, 22-77 years) and the majority were female (81%). Best responses included partial response (18.8%), stable disease for <6 months (25.0%), and progressive disease (56.3%). Median OS was 7.5 months (95% CI 3.4 to 34.6) and median PFS was 1.9 months (95% CI 1.8 to 11.8). PFS in responding patients was 11.8, 18.9, and 34.6 months. Available genomic sequencing showed TSC, ATRX, and TP53 mutations; no TFE3 fusions were identified (N=7). Nearly all patients experienced a treatment-related adverse event (AE) of any grade, while 37.5% experienced a grade 3-4 AE. Most common AEs were fatigue (43.8%), pruritus (37.5%), rash (25.0%), and aspartate aminotransferase increase (25.0%). There were no grade 5 AEs. CONCLUSIONS: The combination of ipilimumab and nivolumab demonstrated responses in 18.8% of patients with advanced malignant PEComas. Dual immunotherapy may be an alternative treatment option for certain patients, including those who are unable to tolerate or do not desire prolonged treatment with chemotherapy or mTOR inhibition or have failed to respond to other therapies. Ipilimumab and nivolumab warrants further investigation in this and other rare soft tissue sarcomas.