A Phase 1a/1b Open-Label Study Evaluating the Safety, Tolerability, Pharmacokinetics, and Efficacy of BBO-10203 in Subjects With Advanced Solid Tumors (The BREAKER-101 Study)

Inclusion Criteria: * Locally advanced and unresectable or metastatic HER2-positive advanced breast cancer (aBC), HR-positive/HER2-negative advanced breast cancer, KRAS mutant advanced colorectal cancer (aCRC), or KRAS mutant advanced non-small cell lung cancer (aNSCLC) * Measurable disease by RECIST v1.1 (except for HR-positive HER2-negative aBC where evaluable bone-only disease is permitted) * Eastern Cooperative Oncology Group (ECOG) performance status (PS) 0-1 * Adequate LVEF assessed by ECHO or MUGA (BBO-10203 + Trastuzumab cohorts only) * Stable brain metastases * Patients with HER2-positive aBC: Must have had at least 2 prior lines of anti-HER2-directed therapy. Only 1 prior line is acceptable where there is no other regionally available standard of care (SoC) * Monotherapy Cohort patients with HR-positive, HER2-negative aBC, KRAS mutant aCRC or aNSCLC: Must have progression on, or disease recurrence after at least one line of SOC treatment or in the opinion of the investigator, would be unlikely to tolerate or derive clinically meaningful benefit from SoC therapy * BBO-10203 + Fulvestrant combination cohort patients with HR-positive, HER2-negative aBC: confirmed PIK3CA mutation, must have been treated with a CDK4/6i * BBO-10203 + Fulvestrant + ribociclib combination cohort patients with HR-positive, HER2-negative aBC: confirmed PIK3CA mutation, no prior systemic therapy in the aBC setting permitted * BBO-10203 + FOLFOX + Bevacizumab combination cohort patients with KRAS mutant aCRC: One prior line of irinotecan-containing therapy for locally advanced or metastatic CRC is allowed but not required Exclusion Criteria: * Patients with KRAS mutant aCRC who have KRAS G12R mutation, BRAFV600E mutation, HER2amp, or dMMR/MSI-H tumors * Patients with KRAS mutant aNSCLC who have KRAS G12R mutation, or tumors with other targetable driver mutations (eg, EGFR, anaplastic lymphoma kinase, ROS1/BRAF/RET/MET/EGFR exon20 insertion/NTRK/HER2) * Patients with untreated and/or non-stable brain metastases Other inclusion/exclusion criteria are specified in the protocol