Inclusion Criteria:

1. * ECOG performance status 0-1
2. * Life expectancy \>3 months
3. * One the following histologically or cytologically confirmed advanced solid tumors: head and neck squamous cell carcinoma, colorectal adenocarcinoma, pancreatic adenocarcinoma, NSCLC, breast carcinoma (HR+ and HER2- that has progressed to a prior treatment with CD4/CDK6 inhibitor), or ovarian epithelial carcinoma
4. * Patients must have disease that is advanced (ie, surgery or radiotherapy are not considered to be potentially curative), recurrent, or metastatic following SoC treatments
5. * Adequate hematological, liver, and renal function
6. * Participant must have tumor lesion(s) or metastases amenable to biopsy, excluding bone metastases

Exclusion Criteria:

1. * Active and clinically significant (CS) infection
2. * Refractory nausea and/or vomiting, chronic gastrointestinal disease, or previous significant bowel resection, with CS sequelae that would preclude adequate absorption of GTAEXS617
3. * Symptomatic central nervous system (CNS) malignancy or metastases
4. * Concurrent active or previous malignancy
5. * Prior organ or allogeneic stem-cell transplantation
6. * Moderate or severe cardiovascular disease
7. * Received anticancer therapy within 28 days or 5 half-lives (whichever is shorter) before the first dose of the study treatment
8. * Received treatment with known strong inhibitors and or inducers of cytochrome P450 3A isoform subfamily (CYP3A) within 14 days or 5 half-lives before the first dose of study treatment
9. * Received treatment with known inhibitors or inducers of P-glycoprotein (P-gp) or breast cancer resistance protein (BCRP) within 14 days or 5 half-lives before the first dose of study
10. * Received treatment with known substrates of organic anion transporting peptide 1B3 (OATP1B3) or BCRP within 14 days or 5 half-lives before the first dose of study treatment
11. * Unresolved or unstable serious toxic side-effects of prior chemotherapy or radiotherapy
12. * Has had or is scheduled to have major surgery \<28 days prior to the first dose of study treatment