Nivolumab or Expectant Observation Following Ipilimumab, Nivolumab, and Surgery in Treating Patients With High Risk Localized, Locoregionally Advanced, or Recurrent Mucosal Melanoma

Inclusion Criteria: * STEP 1 ELIGIBILITY CRITERIA * Documentation of disease: * Histologic documentation: histologically proven mucosal melanoma by local pathology * Tumor tissue: tumor tissue from the primary site of disease must be available for PD-L1 testing (stratification factor) * Disease status * Tumors must have NOT been completely resected, or must be locoregionally recurrent if previously resected; tumor must be deemed potentially resectable by local surgeon * MM arising from the head/neck, genitourinary, or gastrointestinal tract * Disease meets any 1 of 4 characteristics: * Regional lymph node (LN) involvement; OR * Multifocal/satellite primary disease; OR * Single localized, primary disease meeting one of the following site-specific requirements: * Head/neck - any primary lesion if sinonasal; pT4a or above for nasal or oral cavity * Anorectal - any primary lesion * Conjunctiva - any primary lesion T2 or T3 stage by American Joint Committee on Cancer (AJCC) * Vaginal/cervical - any primary * Vulvar (hair bearing surface, labia majora) - AJCC cutaneous stage IIB or higher * Esophageal - any primary * Locoregionally recurrent following prior resection * No evidence of metastatic disease at the time of registration * No prior medical therapy (chemotherapy, immunotherapy, biologic or targeted therapy) or radiation therapy for MM, unless locoregionally recurrent; if recurrent, no prior medical or radi…