A First-in-Human Phase 1 Safety and Biodistribution of [177Lu]Lu-ABY-271 in Subjects With HER2-positive Metastatic Breast Cancer

Inclusion Criteria: * Subject has unresectable locally advanced or metastatic breast cancer * Subject with histologically or cytologically confirmed carcinoma with documented HER2 overexpression (biopsy not older than 2 years): immunohistochemistry (IHC) score 3+; OR 2+ and fluorescence in situ hybridization (ISH) positive * At least one known tumor lesion ≥ 15 mm * Eastern Cooperative Oncology Group (ECOG) performance status ≤ 2 Part A only \- Subject is in treatment, or planned to start a new line of standard systemic anti-tumor therapy Part B only * Subject has progressive disease, documented radiologically in the last three months * Subject has received at least 3 lines of standard systemic anti-tumor therapy in the palliative setting * Subject has received last dose of previous line of systemic anti-tumor therapy, and has no ongoing treatment related toxicities \> grade 1 (except alopecia) prior to planned first dose of \[177Lu\]Lu-ABY-271 Exclusion Criteria: * Active brain metastases * Administration of another IMP within 5 half-lives (for experimental biologics: 6 months or 5 half-lives, whichever is longer) of the planned first dose of \[177Lu\]Lu-ABY-271 * Exposure to any anti-tumor therapy since the last documented progression, including any radiotherapy within 7 days prior to the planned first dose of \[177Lu\]Lu-ABY-271