An Investigational Study of BG-75202 Alone and in Combination With Other Therapeutic Agents in Adults With Advanced Solid Tumors

The purpose of this study is to evaluate the safety, tolerability, pharmacokinetics (PK), pharmacodynamics, and preliminary antitumor activity of BG-75202 (KAT6A/B inhibitor) alone and in combination with other therapies in participants with breast cancer and other advanced solid tumors.

Inclusion Criteria: * Part 1A: Participants with histologically or cytologically confirmed advanced, metastatic breast cancer and other solid tumors who have exhausted, are intolerant of all available standard of care therapies, and/or without available standard of care therapies. * Part 1B and Part 2A: Participants with advanced breast cancer with 1 to 3 prior lines of systemic therapy in the metastatic setting. Prior lines in the advanced/ metastatic setting may not exceed 2 lines of chemotherapy (inclusive of antibody-drug conjugate with cytotoxic payload). * Parts 2B and 2C: Participants with advanced breast cancer enrolled in regions where cyclin-dependent kinase 4/6 (CDK4/6) inhibitors are not approved and/or not available as the first-line treatment and who are CDK4/6 inhibitor treatment naïve and did not receive any previous systemic treatment for advanced disease. * Participants with breast cancer must have histologically or cytologically confirmed advanced breast cancer at the time of most recent testing, based on American Society of Clinical Oncology (ASCO)/College of American Pathologists (CAP) guidelines. * Female participants with metastatic breast cancer must be postmenopausal or receiving ovarian function suppression treatment. * Measurable disease as assessed by Response Evaluation Criteria in Solid Tumors (RECIST) v 1.1. * Stable Eastern Cooperative Oncology Group (ECOG) Performance Status of 0 or 1. * Adequate organ function. Exclusion Criteria: * Prior exposure to KAT6A/B or KAT7 inhibitors/degraders. * Patients with active leptomeningeal disease or uncontrolled, untreated brain metastasis. * Participants with any malignancy ≤ 3 years before screening for the study except for the specific cancer under investigation in this study and any locally recurring cancer that has been treated curatively which in the opinion of the investigator is unlikely to require intervention during the study. Note: Other protocol defined Inclusion/Exclusion criteria may apply.