A subtype of hormone receptor-positive breast cancer. Luminal B breast cancer cells typically have estrogen receptor (ER) proteins but not progesterone receptor (PR) proteins inside them. The cancer cells may or may not have the HER2 protein on their surface. Luminal B breast cancer grows faster and responds less to hormone therapy than Luminal A. Learn how it’s diagnosed, treated, and what to expect. Luminal B breast cancers have a worse prognosis than luminal A tumors. Luminal B breast cancer may not respond as well to hormone therapy as luminal A breast cancer. However, they are more likely to respond to chemotherapy. Approximately 15 to 20 percent of tumors are classified as luminal B. Luminal B breast cancer is a subtype characterized by hormone receptor positivity and HER2 status. It makes up about 10% of breast cancers and is more aggressive than Luminal A. Read on to learn what it means to have luminal B breast cancer, how it’s diagnosed, and what you can expect from treatment. Luminal B breast cancer is a subtype of breast cancer named for the genes the cancer cells express. It’s also called group 2 or HR+/HER2+ breast cancer. About 10 percent of breast cancer cases are luminal B, according to the National Cancer Institute (NCI) Surveillance, Epidemiology, and End Results (SEER) database. One specific type is luminal B breast cancer. It’s less common than luminal A, but often more aggressive. Personalizing breast cancer treatment for patients with luminal B is an important goal as researchers seek to uncover better ways to detect and treat it. Luminal B breast cancer is a subtype of hormone receptor-positive (HR+) breast cancer. It usually responds to hormone therapy and has a good overall survival rate. Luminal A and Luminal B breast cancers are both ER-positive subtypes but differ fundamentally in their proliferation rates, progesterone receptor expression. Luminal B breast cancers are positive for one of the hormone receptors: either estrogen or progesterone. In most cases, luminal B breast cancers are estrogen receptor-positive, but some are progesterone receptor-positive.