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.