A Study With NKT5097 for Adults With Advanced/Metastatic Solid Tumors

The goal of this open-label dose escalation and expansion study is to evaluate the safety and tolerability of NKT5097 in adults with advanced/metastatic tumors (emphasis on breast cancer and solid tumors with CCNE1 amplification). Main questions to answer include: * What is the recommended dose for expansion and/or Phase 2, for both monotherapy and in combination with ET * What medical issues/symptoms do participants experience when taking NKT5097 as monotherapy as well as in combination with ET

Inclusion Criteria: * Able to provide written informed consent * Advanced unresectable or metastatic solid tumor (Part 1, 2 \& 3 only) * Advanced unresectable or metastatic HR+/HER2- breast cancer (Part 4 \& 5 only) * Refractory to or unable to tolerate existing therapies (Part 1, 2 \& 4 only) * Measurable or evaluable disease (Part 1, 2, \& 4 only). * Measurable disease (Part 3 \& 5 only) * Eighteen years of age or older * ECOG status of 0 or 1 * Adequate organ function * Patients with female reproductive organs must be surgically sterile, post- menopausal or willing to use effective contraception per protocol * Patients who are capable of insemination must be willing to use highly effective contraception and to refrain from sperm donation during treatment and for 28 days after the last dose * Able to swallow oral meds * Willing to provide tumor tissue Exclusion Criteria: * Advanced solid tumor that is a candidate for curative treatment * History of another malignancy except for the following: adequately treated local basal cell or squamous carcinoma of the skin, in situ cervical cancer, adequately treated papillary noninvasive bladder cancer, other adequately treated Stage I or Stage II cancers currently in complete remission * Not recovered from the effects of prior anticancer therapy * Clinically significant cardiovascular event, including myocardial infarction, arterial thromboembolism, or cerebrovascular thromboembolism, within 6 months * Known active CNS metastases and/or carcinomatous meningitis * Active interstitial lung disease requiring treatment * History of uveitis, retinopathy, or other clinically significant retinal disease * Major surgery within 30 days of administration of first dose * Active uncontrolled infectious disease * Significant liver disease (Child Pugh class B or C) * Should not have received any prior selective investigational inhibitors or degraders (Part 5 only)