A Study to Investigate the Safety, Pharmacokinetics, and Preliminary Efficacy of IDE574 Therapy in Adult Participants With Advanced Solid Tumors

Inclusion Criteria:

Archival Tissue sample for testing

* Part 1A - Participants with advanced or metastatic ER+, HER2- breast cancer, NSCLC, CRPC, and MSS colorectal adenocarcinoma who have progressed on/after at least one line of standard of care therapy or are intolerant to additional effective therapies.
* Parts 1B, 2A and 2B: Participants with ER+, HER2- breast cancer who have progressed after at least 1 prior line of treatment with an endocrine therapy and a CDK4/6 inhibitor
* Female participants with ER+, HER2- breast cancer considered to be of childbearing potential (or have tubal ligations only) must be willing to undergo medically induced menopause (Parts 2A and B only)
* Female participants of nonchildbearing potential with ER+, HER2- breast cancer must meet at least 1 of the following criteria: Age ≥ 60 years or age \<60 years with absence of menstruation for at least 12 months, or had prior removal of both ovaries
* Have Eastern Cooperative Oncology Group performance status (ECOG PS) of ≤1.
* Have adequate bone marrow, renal and liver function.
* Life expectancy of \>3 months
* Able to safely administer and retain orally administered study treatment
* Able to comply with contraceptive/barrier requirements

Key Exclusion Criteria:

* Known symptomatic brain metastases or leptomeningeal metastasis
* Known primary CNS malignancy and any other malignancies within 2 years prior to the first dose with the exception of adequately treated localized tumor.
* Have impairment of GI function or GI disease that may significantly alter the absorption of IDE574.
* Have active liver or biliary disease.
* Have active, uncontrolled bacterial, fungal, or viral infection
* Have clinically significant cardiac abnormalities and/or blood clotting events within 6 months before the first dose
* If participants had adverse reactions to previous experimental antitumor treatment that have not recovered to Grade ≤ 1
* Prior irradiation to \>25% of the bone marrow.
* Known or suspected hypersensitivity to IDE574/excipients or components (Parts 1 \& 2) or fulvestrant/excipients or components (Part 2 only)