The Evaluation of PC14586 in Patients With Advanced Solid Tumors Harboring a TP53 Y220C Mutation (PYNNACLE)

Inclusion Criteria: * At least 18 years of age or 12 to 17 years of age after Safety Review Committee approval. * Locally advanced or metastatic solid malignancy with a TP53 Y220C mutation * Eastern Cooperative Oncology Group (ECOG) status of 0 or 1Performance status * Previously treated with one or more lines of anticancer therapy and progressive disease * Adequate organ function * Measurable disease per RECIST v1.1 (Phase 2) Additional Criteria for Inclusion in Phase 1b (rezatapopt) + pembrolizumab combination) * Anti-PD-1/PD-L1 naive or must have progressed on treatment * Measurable disease Exclusion Criteria: * Anti-cancer therapy within 21 days (or 5 half-lives) of receiving the study drug * Radiotherapy within 14 days of receiving the study drug * Primary CNS tumor * History of leptomeningeal disease or spinal cord compressionBrain metastases * Brain metastases, unless neurologically stable and do not require steroids to treat associated neurological symptoms * Stroke or transient ischemic attack within 6 months prior to screening * Heart conditions such as unstable angina within 6 months prior to screening, uncontrolled hypertension, a heart attack within 6 months prior to screening, congestive heart failure, prolongation of QT interval, or other rhythm abnormalitiesCardiac * Strong CYP3A4 inducers and strong CYP2C9 inhibitors/inducers within 14 days of first dose of rezatapopt * History of gastrointestinal (GI) disease that may interfere with absorption of study drug or patients unable to take oral medication * History of prior organ transplant * Known, active malignancy, except for treated cervical intraepithelial neoplasia, or non-melanoma skin cancerPrior malignancy * Known, active uncontrolled Hepatitis B, Hepatitis C, or human immunodeficiency virus infection Additional Criteria for Exclusion from Phase 2 (rezatapopt monotherapy) * Known KRAS mutation, defined as a single nucleotide variant (SNV) (Phase 2). Exception: Ovarian cancer patients with a known KRAS SNV are permitted. Additional Criteria for Exclusion from Phase 1b (rezatapopt) + pembrolizumab combination) * Received prior therapy with an anti-PD-1, anti-PD-L1, or anti-PD-L2 agent or with an agent directed to another stimulatory or co-inhibitory T-cell receptor and discontinued from that treatment due to a Grade 3 or higher immune-related AE (irAE) * Received a live or live-attenuated vaccine within 30 days prior to the first dose of study intervention * Diagnosis of immunodeficiency or receiving chronic systemic steroid therapy within 7 days prior to the first dose of study drug * Hypersensitivity (≥ Grade 3) to pembrolizumab and/or any of its excipients * Active autoimmune disease that has required systemic treatment in past 2 years * History of radiation pneumonitis * History of (non-infectious) or active pneumonitis / interstitial lung disease that required steroids * Active infection requiring systemic therapy * Known history of HIV infectionHIV * Has previously received rezatapopt