A Study of BG-75098 Alone and in Combination With Other Agents in Adults With Advanced Solid Tumors

The purpose of this study is to evaluate safety, tolerability, pharmacokinetics (PK), pharmacodynamics, and preliminary antitumor activity of BG-75098 alone and in combination with BGB-43395 and fulvestrant in participants with advanced solid tumors.

This study will be conducted in 2 phases: Phase 1a Dose Escalation and Phase 1b Dose Expansion.

Inclusion Criteria: * Participants must have measurable disease as assessed by RECIST v1.1. * Participants must have a stable Eastern Cooperative Oncology Group (ECOG) Performance Status of 0 or 1. * Participants must have adequate organ function. * Dose Escalation Part A: Participants with histologically or cytologically confirmed advanced, metastatic, or unresectable solid tumors potentially associated with cyclin-dependent kinase 2 (CDK2) dependency. Participants should have received prior treatment with available standard-of-care (SOC) systemic therapies for advanced/metastatic disease, or for whom standard therapy is not available or not tolerated. * Dose Escalation Part B: Patients with histologically or cytologically confirmed advanced, metastatic, or unresectable solid tumors who have received ≥ 1 prior line of systemic therapy in the metastatic setting. * Dose Expansion Cohort 1: Participants with histologically or cytologically confirmed advanced, metastatic, or unresectable CDK4/6 inhibitor-progressed solid tumors. * Dose Expansion Cohort 2: Participants with advanced solid tumors. Participants with primary platinum refractory disease are not eligible. Participants should have received ≥ 1 line of platinum-containing chemotherapy and ≤ 4 prior therapeutic regimens in the advanced/metastatic setting. Exclusion Criteria: * For all cohorts: Prior therapy selectively targeting CDK2 inhibition or degradation. * For combination cohorts: Prior therapy selectively targeting CDK4. Prior CDK4/6 inhibitor standard of care therapy is permitted and required in local regions where it is approved and available. * Participants with active leptomeningeal disease or uncontrolled, untreated brain metastasis. NOTE: Other protocol defined Inclusion/Exclusion criteria may apply.