Luminal A breast cancer

Researchers have identified four main molecular subtypes of breast cancer (also known as the intrinsic subtypes). The luminal A subtype, which is the most common, is usually estrogen receptor–positive and HER2-negative and has low levels of the Ki-67 protein that affects cell proliferation. These tumors do not grow quickly, have a lower risk of returning, and tend to respond well to hormone therapy. This subtype accounts for about 50 to 60 percent of all breast cancers and has a very good prognosis.