The purpose of this study is to evaluate the safety, tolerability, pharmacokinetic (PK), and pharmacodynamic (PD) profiles of escalating doses of RMC-5552 monotherapy in adult participants with relapsed/refractory solid tumors and to identify the recommended Phase 2 dose (RP2D).

This is an open-label, multicenter, Phase 1/1b study of RMC-5552 monotherapy in participants with advanced relapsed or refractory solid tumors. The study will include 2 components: 1) a Dose-Escalation Component for participants with relapsed or refractory solid tumors and 2) a Dose-Expansion Component for participants with relapsed or refractory solid tumors harboring certain specific mutations/rearrangements that result in hyperactivation of the mTOR pathway. Participants will be treated until disease progression per RECIST v1.1, unacceptable toxicity, or other criteria for withdrawal are met, whichever occurs first.

Inclusion Criteria:

• Participants (male or female) ≥18 years of age
• Participants who have advanced solid tumors that have failed, are intolerant to, or are considered ineligible for standard of care anticancer treatments including approved drugs for oncogenic drivers in their tumor type
• Eastern Cooperative Oncology Group (ECOG) performance status of 0 to 1
• Participants in the Dose-Expansion Component must have molecular aberrations in the mTOR pathway
• Adequate hematologic, hepatic and renal function

Exclusion Criteria:

• Known or suspected leptomeningeal or brain metastases or spinal cord compression
• Primary central nervous system (CNS) tumors
• Clinically significant cardiac disease
• Active, clinically significant interstitial lung disease or pneumonitis
• Subjects with abnormal fasting glucose, type 1 diabetes, or uncontrolled type 2 diabetes are excluded.
• Subjects with stomatitis or mucositis of any grade