Dose Determining Study of EXS74539 (REC-4539) in Participants With Select Solid Tumors

Key Inclusion Criteria:

* Eastern Cooperative Oncology Group (ECOG) performance status of 0-1.
* Histologically confirmed diagnosis of the following solid tumors:

  * SCLC
  * High grade neuroendocrine or small cell carcinomas of non-lung origin
  * Non-small cell lung cancer \[NSCLC\]
  * Prostate cancer
  * Ovarian cancer
  * Renal carcinoma \[clear and non-clear cell\]
  * Head and neck squamous cell carcinoma
  * Hepatic cancer
  * Gastric cancer
  * Triple-negative breast cancer \[TNBC\]
* Participant disease should have progressed, relapsed or the participants should have been intolerant to at least one prior standard systemic therapy for their respective underlying malignancy.
* Measurable disease per Response Evaluation Criteria in Solid Tumors (RECIST) version 1.1.

Key Exclusion Criteria:

* Any medical or psychiatric condition that, in the opinion of the Investigator, could jeopardize or would compromise the participant's safety or ability to participate in the study.
* Symptomatic brain metastases, leptomeningeal metastases, or spinal cord compression due to disease. Participants with brain metastases must be clinically stable and off corticosteroids and anticonvulsants for ≥1 month prior to study treatment and not require any specific intervention for brain metastases.
* Active and clinically significant infection requiring systemic antibacterial, antiviral, or antifungal therapy \<7 days of the first scheduled dose of the study treatment.
* Significant cardiac abnormalities.
* Major surgery within 28 days prior to the start of study treatment.

Note: Other protocol-defined inclusion and exclusion criteria may apply.