Trial of BDC-1001 +/- Pertuzumab in Subjects With HER2-Positive Metastatic Breast Cancer

Key Inclusion Criteria: Histologically confirmed adenocarcinoma of the breast that is HER2+ (IHC 3+ or gene amplification by ISH or NGS). Have received 2 or more prior lines of anti-HER2-directed therapies, at least 1 in the metastatic setting and including trastuzumab deruxtecan. Measurable disease as determined by RECIST v.1.1. Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1. Have life expectancy of greater than 12 weeks per the Investigator. All subjects must agree to have a biopsy prior to enrollment. If, in the judgment of the Investigator, a biopsy is not safely accessible or clinically feasible an archival tumor tissue sample must be submitted in lieu of a freshly collected specimen. Key Exclusion Criteria: History of severe hypersensitivity to any ingredient of BDC-1001 or pertuzumab. Previous treatment with a small molecule TLR7/8 agonist or TLR7/8 agonist that has been conjugated to tumor-targeting antibody such as ISACs within 12 months before starting study treatment. Impaired cardiac function or history of clinically significant cardiac disease. Human Immunodeficiency virus (HIV) infection, active hepatitis B infection, or hepatitis C infection. Central nervous system metastases with the exception of disease that is asymptomatic, clinically stable, and has not required steroids for at least 28 days before starting study treatment.