The main purpose of the study is to assess whether the study drug, ERAS-4001, is safe and tolerable when administered to patients with advanced or metastatic solid tumors with certain KRAS mutations. ERAS-4001 will be given alone or in combination with other treatments.

This is a first-in-human, Phase 1/1b, open-label, multicenter clinical study of ERAS-4001 as a monotherapy and in combination with other cancer therapies. The study will commence with dose optimization of ERAS-4001 monotherapy, followed by dose optimization of ERAS-4001 in combination with other cancer therapies.

Inclusion Criteria:

• Age ≥ 18 years
• Willing and able to give written informed consent
• Pathological documentation of tumor type and mutation prior to the first dose of study drug(s)
• There is no available standard systemic therapy available for the patient's tumor histology and/or molecular biomarker profile; or standard therapy is intolerable, not effective, or not accessible; or patient has refused standard therapy
• Able to swallow oral medication
• Have Eastern Cooperative Oncology Group Performance Status (ECOG PS) of 0 or 1
• Adequate cardiovascular, hematological, liver, and renal function
• Willing to comply with all protocol-required visits, assessments, and procedures

Exclusion Criteria:

• Previous treatment with a RAS inhibitor
• Is currently receiving another study therapy or has participated in a study of an investigational agent and received study therapy within 4 weeks of the first dose of ERAS-4001
• Received prior palliative radiation within 14 days of Cycle 1, Day 1
• Have primary central nervous system (CNS) tumors
• Prior surgery (e.g., gastric bypass surgery, gastrectomy) or gastrointestinal dysfunction (e.g., Crohn's disease, ulcerative colitis, short gut syndrome) that may affect drug absorption
• Have any underlying medical condition, psychiatric condition, or social situation that, in the opinion of the Investigator, would compromise study administration as per protocol or compromise the assessment of AEs
• Are pregnant or breastfeeding or expecting to conceive or father children within the projected duration of the trial