Human epidermal growth factor receptor 2 (HER2)-negative subset is the most heterogeneous group of metastatic breast cancers (MBCs) as it includes both hormone receptor (HR)-positive and HR-negative breast cancer (or TNBC), which have different therapies and treatment challenges. Though endocrine therapy (ET) remains the treatment backbone in HR-positive HER2-negative cases, about 40% of the patients show intrinsic or acquired resistance to ET due to multiple mechanisms. Combining different therapies such as ET and other targeted therapies with or without chemotherapy fails to give continued benefit, unlike cyclin-dependent kinase (CDK) 4/6 inhibitors that have shown a great benefit. TNBC has conventionally been treated ineffectively with systemic chemotherapy. Recently, poly (ADP-ribose) polymerase inhibitors (PARPi) have emerged for HER2-negative breast cancer (BC) patients, including TNBC. Olaparib and talazoparib have recently been approved in germline BRCA-mutated (gBRCAm) HER2-negative MBC. Additionally, ongoing trials of PARPi in combination with various therapies are expected to provide more and better treatment options for gBRCAm HER2-negative breast cancer.
Keywords: HER2-negative breast cancer; HR-positive HER2-negative breast cancer; PARP inhibitors; TNBC; olaparib; talazoparib.