Using Biomarkers to Help Guide Safe Immunotherapy Discontinuation in Patients With Unresectable Stage IIIB-IV Melanoma, The PET-Stop Trial

Inclusion Criteria: * STEP 0 PRE-REGISTRATION INCLUSION CRITERIA * Patient must have active advanced melanoma, defined as unresectable stage IIIB-IV by American Joint Committee on Cancer (AJCC) 8th edition * Patient must have melanoma originating from cutaneous, acral-lentiginous, or mucosal primary sites. Patients with melanoma of unknown primary site are eligible. Patients must not have melanoma from an ocular primary site * Patient must have had measurable disease by immune related Response Evaluation Criteria in Solid Tumors (imRECIST) prior to start of initial anti-PD-1 therapy * Patient must be actively receiving standard of care anti-PD-1 therapy, currently be 52 weeks (+/- 2 weeks) from start of anti-PD-1 therapy, and have not experienced a toxicity that prevents them from continuing on therapy. Permitted systemic anti-PD-1 therapy regimens include: * Nivolumab 240 mg IV every (Q)2weeks or 480 mg IV Q4weeks * Pembrolizumab 200 mg IV Q3weeks or 400 mg IV Q6weeks * Nivolumab 1 mg/kg plus ipilimumab 3 mg/kg IV Q3weeks induction x 4 doses, followed by nivolumab 240 mg IV Q2weeks or 480 mg IV Q4weeks maintenance * Nivolumab 3 mg/kg plus Ipilimumab 1 mg/kg IV Q3weeks induction x 4 doses, followed by nivolumab 240 mg IV Q2weeks or 480 mg IV Q4weeks maintenance * Pembrolizumab 2 mg/kg (or 200 mg flat dose) plus Ipilimumab 1 mg/kg IV Q3weeks induction x 4 doses, followed by pembrolizumab 200 mg IV Q3weeks or 400 mg IV Q6weeks maintenance * Patient must have an East…