Gastroenteropancreatic Neuroendocrine Tumor

Immune checkpoint inhibitors (ICI) have revolutionized the management of advanced cancers. However, most rare cancers have been excluded from this progress due to the lack of clinical trials involving these diseases. After the standard first-line treatment, there are no other validated treatments for most of them. The management of these patients in ≥ 2nd line treatment relies on historic poorly effective regimens. This creates an inequity between patients with frequent cancers beneficiating from medical progresses and approvals of innovative drugs, and patients with rare cancers are still treated with old and toxic drugs. Few available data on case reports and early phase studies indicate a beneficial role of the immunotherapy in rare cancers. The investigators assume that the combination of Domvanalimab and Zimberelimab is more effective than historical standard treatments in patients with 5 types of advanced rare cancers, after failure of at least one line of standard treatment in the advanced setting: * Cohort 1: Peritoneal Mesotheliomas (PM) * Cohort 2: Gestational Trophoblastic Tumors (GTT) * Cohort 3: B3 Thymomas and Thymic Carcinomas (TET) * Cohort 4: Refractory Thyroid