Triple Immune Checkpoint Inhibition for Advanced or Metastatic PD-(L)1 Refractory Merkel Cell Carcinoma

Inclusion Criteria: * Presence of histologically confirmed, advanced or metastatic Merkel cell carcinoma (MCC), which is considered incurable with standardly available therapies * Presence of at least one MCC tumor, considered measurable per Response Evaluation Criteria in Solid Tumors (RECIST) version (v)1.1 * Age 18 or older. (NOTE: Both men and women, and members of all races and ethnic groups are eligible for this trial.) * Eastern Cooperative Oncology Group (ECOG) performance score of 0-2 * Must have previously received at least one prior systemic treatment regimen with an anti-PD-(L)1 agent (administered as monotherapy or in combination with another treatment) * Must meet the following criteria defining anti-PD-(L)1 refractory MCC: Best response of progressive disease (PD) or development of PD after best response of complete response (CR), partial response (PR), or stable disease (SD) after receiving at least 6 weeks of therapy with an anti-PD-(L)1 agent; PD must develop within 6 months of the last administration of anti-PD-(L)1 agent * Absolute neutrophil count (ANC) \>= 1 x 10\^9/L * Platelet count \>= 100 × 10\^9/L * Hemoglobin \>= 9 g/dL (may have been transfused) * Alanine aminotransferase (ALT), aspartate aminotransferase (AST) and total bilirubin level =\< 2 x the upper limit of normal (ULN) (or total bilirubin =\< 2.5 x ULN in patients with Gilbert's syndrome, and AST, ALT =\< 2.5 x ULN in patients with hepatic metastases) * Estimated creatinine clearance \>= 3…