Inclusion Criteria:  Male or female and ≥12 years-of-age at the time of informed consent. Lansky performance status ≥50% for patients ≤16 years of age, or ECOG score of 0, 1, or 2 for patients >16 years of age. Locally advanced or metastatic resistant or refractory solid tumors. Patients <18 years of age must weigh at least 40 kg. Submission of available tumor tissue at screening or willingness to have a biopsy performed if safe and feasible Next generation sequencing (NGS) report obtained in a CLIA-certified or equivalent laboratory demonstrating eligible tumor biomarker. Measurable disease as per RECIST v1.1. Ability to swallow and retain oral medications. Acceptable hematologic and organ function at screening. Negative pregnancy test (serum) for women of childbearing potential (WOCBP) at Screening. Resolution of all toxicities of prior therapy or surgical procedures. Any prior radiation must have been completed at least 7 days prior to the start of study drugs, and patients must have recovered from any acute adverse effects prior to the start of study treatment.  Exclusion Criteria:  Chemotherapy or small molecule antineoplastic agent given within 21 days or <5 half-lives, whichever is shorter, prior to first dose of study drug. History or current condition, therapy, or laboratory abnormality that might confound the study results or interfere with the patient's participation for the full duration of the study treatment. Patients who are pregnant or breastfeeding. Life-threatening illness, medical condition, active uncontrolled infection, or organ system dysfunction or other reasons which, in the investigator's opinion, could compromise the participating patient's safety. Major surgery within 4 weeks prior to first dose of RP-6306. Uncontrolled, symptomatic brain metastases. Uncontrolled hypertension. Psychological, familial, sociological, or geographical conditions that do not permit compliance with the protocol and/or follow-up procedures outlined in the protocol.