Study of INCB123667 in Subjects With Advanced Solid Tumors

Inclusion Criteria: * Adults aged 18 years or older at the time of the signing of the ICF. * Life expectancy greater than 12 weeks. * ECOG performance status score of 0 or 1. * Disease progression on prior standard treatment, intolerance to or ineligibility for standard treatment, or no available treatment to improve the disease outcome. * Availability of a baseline archival tumor specimen or willingness to undergo a pretreatment and an on-treatment tumor biopsy. For Part 1: Participants in Part 1A (dose escalation): Histologically or cytologically confirmed advanced or metastatic solid tumors. Participants in Part 1B (dose expansion): * Disease Group 1: Ovarian/Fallopian/Primary Peritoneal Cancer * Disease Group 2: Endometrial/Uterine Cancer * Disease Group 3: Gastric, GEJ, and esophageal carcinomas * Disease Group 4: TNBC * Disease Group 5: HR+/HER2- breast cancer * Disease Group 6: Other tumor indications excluding bone cancers For Part 2: Participants in Part 2A (dose escalation): Histologically or cytologically confirmed advanced or metastatic solid tumors. * TGA, TGC, TGE, TGF, and TGG: Participants with HR+/HER2- breast cancer or participants with a different tumor. * TGB and TGD: Participants with HR+/HER2- breast cancer. Participants in Part 2b (dose expansion): * TGH and TGJ: * Participants with HR+/HER2- breast cancer. * Participants with any other advanced or metastatic solid tumor. * TGI and TGK: • Participants with HR+/HER2- breast cancer. * TGL, TGM and TGN: • Participants with advanced or metastatic epithelial ovarian/fallopian/primary peritoneal carcinoma. * Measurable lesions by CT or MRI based on RECIST v1.1 criteria. Exclusion Criteria: * History of clinically significant or uncontrolled cardiac disease. * History or presence of an ECG abnormality that, in the investigator's opinion, is clinically meaningful. * Presence of chronic or current active infectious disease requiring systemic antibiotic, antifungal, or antiviral treatment. * Untreated brain or central nervous system (CNS) metastases or brain or CNS metastases that have progressed. * Known additional malignancy that is progressing or requires active treatment, or history of other malignancy within 2 years of the first dose of study drug. * Specific laboratory values. * Significant concurrent, uncontrolled medical conditions, including but not limited to Hepatic and Gastrointestinal. * Has not recovered to ≤ Grade 1 from toxic effects of prior therapy and/or complications from prior surgical intervention before starting study drug. * Prior treatment with any CDK2 inhibitor. * Any change in endocrine therapy within 5 half-lives or 28 days (whichever is shorter) before the first dose of study drug or any administration of targeted therapy, antibody, or hypomethylating agent to treat the participant's disease within 5 half-lives or 28 days (whichever is shorter) before the first dose of study drug. * Any major surgery within 28 days before the first dose of study drug. * Any prior radiation therapy within 28 days before the first dose of study drug. * Undergoing treatment with another investigational medication or having been treated with an investigational medication within 5 half-lives or 28 days (whichever is shorter) before the first dose of study drug. * Active HBV or HCV infection that requires treatment. * Known history of HIV. * Known hypersensitivity or severe reaction to any component of study treatment or formulation components. Other protocol-defined Inclusion/Exclusion Criteria may apply.