Study of INCB123667 in Subjects With Advanced Solid Tumors

• 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.

• 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.