Molecular Subtypes of Breast Cancer

Researchers have identified five main molecular subtypes of invasive breast cancer. The molecular subtype of an invasive breast cancer is based on the genes the cancer cells express, which control how the cells behave.

Researchers use molecular subtype information when developing treatment standards of care and when developing new treatments.

Read more about each subtype below.

Luminal A breast cancer is estrogen receptor-positive and progesterone receptor-positive, HER2-negative, and has low levels of the protein Ki-67, which helps control how fast cancer cells grow. Luminal A cancers tend grow more slowly than other cancers, be lower grade, and have a good prognosis.

Luminal B breast cancer is estrogen receptor-positive and HER2-negative, and also has either high levels of Ki-67 (which indicate faster growth of cancer cells) or is progesterone receptor-negative.

Luminal B-like breast cancer is estrogen-receptor-positive and HER2-positive and has any level of Ki-67 and may be progesterone receptor-positive or progesterone receptor-negative. Luminal B cancers tend to grow faster than luminal A cancers and have a slightly worse prognosis.

HER2-enriched breast cancer is estrogen receptor-negative and progesterone receptor-negative and HER2-positive. HER2-enriched cancers tend to grow faster than luminal cancers and can have a worse prognosis, but are usually successfully treated with targeted therapy medicines aimed at the HER2 protein.

Triple-negative or basal-like breast cancer is estrogen receptor-negative, progesterone receptor-negative, and HER2-negative. Triple-negative breast cancer is more common in:

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  people with a BRCA1 mutation

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  younger women

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  Black women

Triple-negative breast cancer is considered more aggressive than either luminal A or luminal B breast cancer.