Clinical Efficacy and Safety of Nivolumab in Malignant Non-Pleural Mesothelioma: A Multicenter, Open-Label, Single-Arm, Japanese Phase II Trial (Viola) Protocol.

Background: There is no authorized treatment for malignant non-pleural mesothelioma (MNPM) worldwide. In contrast to malignant pleural mesothelioma, MNPM has not been investigated, and no treatment has been established due to its rarity.

Objectives: This multicenter, open-label, single-arm, Japanese phase II trial aims at evaluating the efficacy and safety of nivolumab, an immune checkpoint inhibitor, in advanced or metastatic MNPM treatment.

Methods: This phase II trial commenced in October 2020. Twenty-three patients with advanced or metastatic MNPM who meet the inclusion and exclusion criteria were enrolled from five institutions within 2 years. Regardless of prior therapy, 240 mg of nivolumab will be administered intravenously to MNPM patients every 2 weeks to investigate its efficacy and safety until disease progression or unacceptable toxicities are detected, or the patient's condition meets the withdrawal criteria.

Results: The primary endpoint is the objective response rate by central assessment following the Response Evaluation Criteria in Solid Tumors version 1.1. The secondary endpoints include disease control rate, overall survival, progression-free survival, adverse events, and treatment-related adverse events.

Conclusions: This is the first prospective investigator-initiated trial to evaluate the effect of nivolumab monotherapy for MNPM.