Inclusion Criteria:  Male or female and ≥18 years-of-age at the time of informed consent. ECOG Performance status 0 or 1. Locally advanced or metastatic resistant or refractory solid tumors. Submission of available tumor tissue at screening or willingness to have a biopsy performed if safe and feasible. 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. Life expectancy ≥12 weeks after the start of the 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. Known sensitivity to any of the ingredients of RP-6306 or gemcitabine. 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 and gemcitabine. Uncontrolled, symptomatic brain metastases. Uncontrolled hypertension. Moderate or severe hepatic impairment Psychological, familial, sociological, or geographical conditions that do not permit compliance with the protocol and/or follow-up procedures outlined in the protocol.