Testing the Combination of Two Anticancer Drugs M1774 (Tuvusertib) and Avelumab to Evaluate Their Safety and Effectiveness in Treating Merkel Cell Skin Cancer, MATRiX Trial

Inclusion Criteria: * REGISTRATION ELIGIBILITY: Patients must have a history of pathologically confirmed locally advanced/unresectable Merkel cell carcinoma or metastatic Merkel cell carcinoma * REGISTRATION ELIGIBILITY: Patients must have evaluable disease per Response Evaluation Criteria in Solid Tumors (RECIST) version (v)1.1 * REGISTRATION ELIGIBILITY: Patients must have had prior treatment with anti-PD-1 or anti-PD-L-1 antibody (e.g., pembrolizumab, avelumab, etc.) and have experienced progressive disease during treatment or within 120 days from the last dose of anti-PD-(L)1 therapy. Anti-PD-(L)1 therapy administered in combination with other agent(s) including ipilimumab is also allowed as prior therapy, if patients experienced progressive disease during treatment or within 120 days from the last dose of anti-PD-(L)1 therapy. The last dose of anti-PD-(L)1 antibody must be ≥ 14 days prior to planned C1D1. If participants are receiving or received cytotoxic chemotherapy as most recent therapy prior to screening for this trial, there must be clinically and/or radiologically documented progressive disease on or after chemotherapy prior to being eligible for this study. If the patient is receiving bridging chemotherapy, the most recent administration must be ≥ 14 days prior to planned cycle 1 day 1 (C1D1) of the clinical trial to be eligible * REGISTRATION ELIGIBILITY: Age \>= 18 years. Because no dosing or adverse event data are currently available on the use of M1774/tuvu…