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)

Prior treatment

• Has a diagnosis of immunodeficiency or is receiving immunosuppressive therapy within 7 days before the first dose of study intervention
• Has known hypersensitivity including previous clinically significant hypersensitivity reaction to treatment with another monoclonal antibody (mAb)
• 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

Other illness

• Has a known additional malignancy that is progressing or requires active treatment within the past 2 years
• 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)

Other

• Has known central nervous system (CNS) metastases and/or carcinomatous meningitis
• Has ocular or mucosal melanoma
• Has only mucosal lesions
• Is not naïve to Talimogene laherparepvec (TVEC) and other oncolytic viruses

• 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 and re-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 all-trans retinoic acid (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)