Study to Assess GTAEXS617 in Participants With Advanced Solid Tumors

The primary purpose of this study is to assess the safety, tolerability, pharmacokinetics (PK) and anti-tumor activity of GTAEXS617 (REC-617) in participants with advanced solid tumors.

Key Inclusion Criteria: * Eastern Cooperative Oncology Group (ECOG) performance status 0-1. * Life expectancy \> 3 months. * One of the following histologically or cytologically confirmed advanced solid tumors: head and neck squamous cell carcinoma (HNSCC), pancreatic adenocarcinoma, non-small cell lung cancer (NSCLC), breast carcinoma (hormone receptor-positive \[HR+\] and Human Epidermal Growth Receptor 2 negative \[HER2-\] that has progressed to a prior treatment with Cyclin-Dependent Kinase 4 (CDK4)/ Cyclin-Dependent Kinase 6 \[CDK6\] inhibitor), or platinum-resistant high-grade epithelial ovarian, primary peritoneal, or fallopian tube cancers (HGSOC), or triple negative breast cancer (TNBC). * Must have disease that is advanced (ie, surgery or radiotherapy are not considered to be potentially curative), recurrent, or metastatic following SoC treatments. * Adequate hematological, liver, and renal function. * Must have tumor lesion(s) or metastases amenable to biopsy, excluding bone metastases. Key Exclusion Criteria: * Active and clinically significant (CS) infection. * Refractory nausea and/or vomiting, chronic gastrointestinal disease, or previous significant bowel resection, with CS sequelae that would preclude adequate absorption of GTAEXS617. * Symptomatic central nervous system (CNS) malignancy or metastases. * Concurrent active or previous malignancy. * Prior organ or allogeneic stem-cell transplantation. * Moderate or severe cardiovascular disease. * Received anticancer therapy within 28 days or 5 half-lives (whichever is shorter) before the first dose of the study treatment. * Received treatment with known strong/moderate inhibitors and/or strong inducers of cytochrome P450 3A isoform subfamily (CYP3A) within 14 days or 5 half-lives before the first dose of study treatment. * 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 treatment. * Received treatment with known substrates of organic anion transporting peptide or BCRP within 14 days or 5 half-lives before the first dose of study treatment. * Unresolved or unstable serious toxic side-effects of prior chemotherapy or radiotherapy * Has had or is scheduled to have major surgery \<28 days prior to the first dose of study treatment. Note: Other protocol Inclusion/Exclusion criteria may apply.