Tebentafusp Regimen Versus Investigator's Choice in Previously Treated Advanced Melanoma (TEBE-AM)

Inclusion Criteria: * HLA-A\*02:01-positive * unresectable Stage III or Stage IV non-ocular melanoma * archival tumor tissue sample or a newly obtained biopsy of a tumor lesion not previously irradiated has been provided. * measurable or non-measurable disease per RECIST 1.1 * Eastern Cooperative Oncology Group (ECOG) performance status score of 0 or 1 * If applicable, must agree to use highly effective contraception * Capable of giving signed informed consent which includes compliance with the requirements and restrictions listed in the Informed Consent (ICF) and protocol * Must agree to provide protocol specified samples for biomarker analyses. Exclusion Criteria: * Pregnant or lactating women * diagnosis of ocular or metastatic uveal melanoma * history of a malignant disease other than those being treated in this study * ineligible to be retreated with pembrolizumab due to a treatment-related AE * known untreated or symptomatic central nervous system (CNS) metastases and/or carcinomatous meningitis * previous severe hypersensitivity reaction to treatment with another monoclonal antibody (mAb) * active autoimmune disease requiring immunosuppressive treatment * known psychiatric or substance abuse disorders * received prior treatment with a licensed or investigative Immune-mobilizing monoclonal T-cell receptor Against Cancer (ImmTAC) medication or who have not completed adequate washout from prior medications. * received chemotherapy or biological cancer therapy (excluding anti-PD(L)1 mAb, ipilimumab, and BRAF TKI regimen) within 14 days of first dose * received cellular therapies within 90 days of study intervention * ongoing Common Terminology Criteria for Adverse Events(CTCAE) Grade ≥ 2 clinically significant who in the opinion of the investigator could affect the outcome of the study * received systemic treatment with steroids or any other immunosuppressive drug within 2 weeks of first dose * have not progressed on treatment with an anti-PD(L)1 mAb * have not received prior treatment with an approved anti-CTLA-4 mAb * have a BRAF V600 mutation, who have not received a prior BRAF/MEK TKI regimen * currently participating or have participated in a study of an investigational agent or using an investigational device within 30 days of the first dose * known history of chronic viral infections such as hepatitis B virus (HBV) or hepatitis C virus (HCV) * known clinically significant pulmonary or cardiac disease or impaired lung or cardiac function * Out of range Laboratory values * history of allogenic tissue/solid organ transplant