Substudy 02C: Safety and Efficacy of Pembrolizumab in Combination With Investigational Agents or Pembrolizumab Alone in Participants With Stage III Melanoma Who Are Candidates for Neoadjuvant Therapy (MK-3475-02C/KEYMAKER-U02)

Inclusion Criteria:

Has histologically or cytologically confirmed melanoma
Has clinically detectable and resectable Stage IIIB or IIIC or IIID melanoma amenable to surgery

Has been untreated for Stage IIIB, IIIC or IIID melanoma

surgical resection of primary melanoma is allowed
prior radiotherapy to the primary melanoma is allowed
Has provided a baseline tumor biopsy
Male participants who receive gebasaxturev are abstinent from heterosexual intercourse or agree to use contraception during the intervention period and for at least 120 days after the last dose of gebasaxturev
Male participants who receive ATRA are abstinent from heterosexual intercourse or agree to use contraception during the intervention period and for at least 7 days after the last dose of ATRA
Female participants are not pregnant or breastfeeding and are either not a woman of child-bearing potential (WOCBP) OR use a contraceptive method that is highly effective or are abstinent from heterosexual intercourse during the intervention period and for at least 120 days after the last dose of pembrolizumab, vibostolimab, gebasaxturev, or MK-4830, favezelimab + pembrolizumab, or 30 days after the last dose of ATRA, whichever occurs last
Has adequate organ function
Has resolution of toxic effect(s) of the most recent prior therapy to Grade 1 or less (except alopecia)

Exclusion Criteria:

Has a diagnosis of immunodeficiency or is receiving immunosuppressive therapy within 7 days before the first dose of study intervention
Has a known additional malignancy that is progressing or requires active treatment within the past 2 years
Has known central nervous system (CNS) metastases and/or carcinomatous meningitis
Has ocular or mucosal melanoma
Has known hypersensitivity including previous clinically significant hypersensitivity reaction to treatment with another monoclonal antibody (mAb)
Has an active autoimmune disease that has required systemic treatment in the past 2 years
Has an active infection requiring systemic therapy
Has known history of human immunodeficiency virus (HIV)
Has known history of hepatitis B
Has a history of (noninfectious) pneumonitis
Has a history of active tuberculosis (TB)
Has received prior systemic anticancer therapy within 4 weeks prior to randomization
Has received prior radiotherapy within 2 weeks of first dose of study intervention
Has had major surgery <3 weeks prior to first dose of study intervention
Has received a live or live-attenuated vaccine within 30 days before the first dose of study intervention
Has participated in a study of an investigational agent within 4 weeks prior to the first dose of study intervention
Has had an allogeneic tissue/solid organ transplant
Has only mucosal lesions
Is not naïve to Talimogene laherparepvec (TVEC) and other oncolytic viruses