A Study to Examine the Safety of Different Doses of BG-68501 Given to Participants With Advanced-Stage Tumors

Part 1 (Dose Escalation) Inclusion Criteria: * Monotherapy Cohorts: Participants with histologically or cytologically confirmed advanced or metastatic solid tumors potentially associated with CDK2 dependency including HR+/HER2- breast cancer, platinum refractory or resistant serous ovarian cancer (PROC), endometrial cancer, and others. Prior available standard-of-care systemic therapies for advanced or metastatic disease are required. The requirements for enrollment into a food effect evaluation cohort are the same as the monotherapy cohorts with the exception that participants with gastric cancer and gastroesophageal adenocarcinoma are excluded. * Combination Cohorts (BG-68501 with fulvestrant with or without BGB-43395): Enrollment is restricted to only participants with HR+/HER2- BC. In regions where approved and available, participants must have received one or more lines of treatment for advanced/metastatic disease as well as prior endocrine therapy and a CDK4/6 inhibitor in either the adjuvant or advanced/metastatic setting. If applicable, the requirements for enrollment into a food effect evaluation cohort are the same as the combination cohorts. Part 1 (Safety Expansion) and Part 2 (Dose Expansion) Inclusion Criteria: * Participants with advanced, non-resectable, or metastatic HR+/HER2- BC or PROC, including fallopian tube or primary peritoneal cancer. * PROC participants must have received: * ≥ 1 line of platinum-containing chemotherapy for advanced disease. *…