Participants with Relapsed Refractory Solid Tumors for Solid Tumors

Single arm, set dose clinical trial of Lamivudine for Relapsed Refractory Solid Tumors. Accrual 6-24 patients, within 2 years, study completion within 3 years at Mount Sinai Health System. Primary Objective: For Phase 1b to determine the safety and tolerability of Lamivudine with continued PD-(L)1 blockade for patients with relapsed/refractory metastatic solid tumors that have progressed on standard PD-(L)1 blockade. For Phase 2, to determine the effect of adding lamivudine to PD-(L)1 blocking agents in patients with relapsed/refractory solid tumors that have progressed on prior PD-(L)1 agents Secondary Objectives (Phase 1b and 2) Assess 1) Safety and Tolerability, 2) Best overall response rate (BORR), 3) Progression-free survival (PFS), 4) Overall survival (OS) and 5) Duration of response following addition of lamivudine to standard PD-(L)1 blocking agents, 6) Disease control rate (DCR).