This is an open-label, multi-center Phase 1a/1b study designed to evaluate the safety, tolerability, preliminary antitumor activity, and PK of BBO-10203 as a single agent and in combination with trastuzumab in patients with locally advanced unresectable or metastatic (ie, advanced) solid tumors. The study includes a dose escalation phase, and an expansion phase.
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
* Eastern Cooperative Oncology Group (ECOG) performance status (PS) 0-1
* Adequate LVEF assessed by ECHO or MUGA
* 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).
* Patients with HR-positive, HER2-negative aBC, KRAS mutant aCRC or aNSCLC: Must have progression on, or disease recurrence after, all available SoC treatments or in the opinion of the investigator, would be unlikely to tolerate or derive clinically meaningful benefit from appropriate SoC therapy.
Exclusion Criteria:
* Patients with HER2+ aBC who have had more than 1 prior line of therapy with an antibody-drug conjugate
* Patients with KRAS mutant aCRC who have BRAFV600E mutation, HER2amp, or dMMR/MSI-H tumors
* Patients with KRAS mutant aNSCLC who have tumors with other targetable driver mutations (eg, EGFR, anaplastic lymphoma kinase, ROS1/BRAF/RET/MET/EGFR exon20 insertion/NTRK/HER2)
* Patients with untreated brain metastases (exceptions apply for HER2+ aBC per protocol)
Other inclusion/exclusion criteria are specified in the protocol
