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 forstandard treatment, or no available treatment to improve the disease outcome.

• Availability of a baseline archival tumor specimen or willingness to undergo apretreatment 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 orparticipants 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/primaryperitoneal 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, isclinically meaningful.

• Presence of chronic or current active infectious disease requiring systemicantibiotic, antifungal, or antiviral treatment.

• Untreated brain or central nervous system (CNS) metastases or brain or CNSmetastases that have progressed.

• Known additional malignancy that is progressing or requires active treatment, orhistory of other malignancy within 2 years of the first dose of study drug.

• Specific laboratory values.

• Significant concurrent, uncontrolled medical conditions, including but not limitedto Hepatic and Gastrointestinal.

• Has not recovered to ≤ Grade 1 from toxic effects of prior therapy and/orcomplications 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 isshorter) before the first dose of study drug or any administration of targetedtherapy, antibody, or hypomethylating agent to treat the participant's diseasewithin 5 half-lives or 28 days (whichever is shorter) before the first dose of studydrug.

• 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 treatedwith an investigational medication within 5 half-lives or 28 days (whichever isshorter) 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 orformulation components.

Other protocol-defined Inclusion/Exclusion Criteria may apply.