A Clinical Study of Ifinatamab Deruxtecan Based Treatment Combinations or as Monotherapy to Treat Metastatic Castrate Resistant Prostate Cancer (mCRPC) (MK-2400-01A/IDeate-Prostate02)

MK-2400-01A Substudy: A Phase 1/2, Open-label Umbrella Substudy of MK-2400-U01 Master Protocol to Evaluate the Safety and Efficacy of Ifinatamab Deruxtecan-based Treatment Combinations or Ifinatamab Deruxtecan Alone in Participants With Metastatic Castration-resistant Prostate Cancer (mCRPC) (IDeate-Prostate02)

The purpose of this substudy is to assess the efficacy and safety of ifinatamab deruxtecan (I-DXd), given alone or with other treatments in participants with metastatic castration-resistant prostate cancer (mCRPC). The goals of this study are to learn about:

• The safety of the study treatment and if people tolerate it.
• A safe dose level of I-DXd that can be used with other treatments.
• Participant levels of prostate specific antigen (PSA) during treatment.

This sub study MK-2400-01A assesses treatments for metastatic castration-resistant prostate cancer (mCRPC).

The master screening protocol is MK-2400-U01

Inclusion Criteria:

The main inclusion criteria include but are not limited to the following:

• Has histologically- or cytologically-confirmed adenocarcinoma of the prostate without small cell histology
• Has prostate cancer progression while on androgen deprivation therapy (ADT) (or post bilateral orchiectomy) within 6 months before Screening
• Has current evidence of distant metastatic disease
• Has received prior treatment with 1 or 2 androgen receptor pathway inhibitors (ARPIs) and progressed during or after treatment
• Participants receiving bone resorptive therapy (including, but not limited to bisphosphonate or denosumab) must have been on stable doses for ≥4 weeks before allocation/randomization
• An Eastern Cooperative Oncology Group (ECOG) performance status of 0 to 1 assessed within 10 days before allocation/randomization
• Has prior treatment with poly-ADP-ribose polymerase inhibitors (PARPi) if indicated by local approved regimen or were deemed ineligible to receive PARPi by the investigator

Exclusion Criteria:

The main exclusion criteria include but are not limited to the following:

• Has any history of interstitial lung disease (ILD)/pneumonitis irrespective of steroid use (except for a history of radiation pneumonitis that did not require steroids), current ILD, clinical or radiographic suspicion of ILD for which the diagnosis of ILD cannot be ruled out
• Clinically severe pulmonary compromise resulting from intercurrent pulmonary illnesses
• Uncontrolled or significant cardiovascular disease
• History of pituitary dysfunction
• Poorly controlled diabetes mellitus
• History or current condition of adrenal insufficiency (eg, Addison's disease)
• Has received prior treatment with taxane-based chemotherapy agent for metastatic castration-resistant prostate cancer (mCRPC).
• Chronic steroid treatment (dose of >10 mg daily prednisone equivalent), except for low-dose inhaled steroids (for asthma/chronic obstructive pulmonary disease), topical steroids (for mild skin conditions), or intra-articular steroid injections
• Received prior radiotherapy within 2 weeks of start of study intervention, or has radiation-related toxicities, requiring corticosteroids
• Known additional malignancy that is progressing or has required active treatment within the past 3 years
• Known active central nervous system (CNS) metastases and/or carcinomatous meningitis
• Active autoimmune disease that has required systemic treatment in the past 2 years
• History of allogeneic tissue/solid organ transplant