M1231 in Participants With Solid Tumors

Inclusion Criteria: For Part 1 and 2: * The Investigator reviews the medical history, menstrual history, and recent sexual activity to decrease the risk for inclusion of a female with an early undetected pregnancy For Part 1: * Locally advanced or metastatic disease that is intolerant or refractory to standard therapy or for which no standard therapy is judged appropriate by the investigator * Participants with solid tumors expressing or likely to expressing EGFR and MUC1, including but not limited to lung cancer, squamous esophageal cancer, head and neck squamous cell carcinoma, breast cancer and ovarian cancer, should be prioritized for enrollment For Part 2: * Cohort A: Participants must have progressed on at least 2 prior lines of therapy * Cohort B: Participants must have progressed on at least 1 prior line of platinum therapy and for microsatellite instability-high (MSI-H) at least 1 prior line with pembrolizumab * Eastern Cooperative Oncology Group (ECOG) Performance Status less than 1 * Tumor accessible for biopsies and agreement to conduct fresh tumor biopsies at Screening and before first dosing Exclusion Criteria: * Participants not recovered from adverse events (AE) (less than or equal to Grade 1) related to previous therapies (excluding Grade 1 neuropathy and alopecia) * Participant has a history of a second malignancy within 3 years before the date of enrollment * Known brain metastasis * Unstable angina, myocardial infarction, congestive heart failure or a coronary revascularization procedure within 180 days of study entry * Cerebrovascular accident/stroke * Diagnosis of fever within 1 week prior to study intervention administration * Life expectancy of less than 4 months * Steroid therapy for anti-neoplastic intent taken less than 7 days prior to the first dose of study intervention * Major surgery within 4 weeks prior to start of study intervention * Received growth factors (including erythropoietin (EPO), darbepoetin, granulocyte-colony stimulating factor (G-CSF), granulocyte macrophage-colony stimulating factor (GM-CSF), and platelet stimulators or transfusions within 2 weeks prior to the first day of study intervention