Estrogen is a hormone that helps control sexual and reproductive health. Estrogen will bind to receptors inside cancer cells, which may cause the cells to grow.

HR- breast cancer is a cancer with cells that do not have hormone receptors. HR- cancer cells do not need hormones, like estrogen and progesterone, to grow.

HR+ breast cancer is cancer with cells that have hormone receptors. HR+ cancer cells need estrogen or progesterone to grow.

HER2 is a protein found in both healthy cells and cancer cells. HER2 plays a role in normal cell growth. In cancer, HER2 amounts are altered, which can cause the growth of cancer cells.

HER2 status means the amount of HER2 proteins found on breast cancer cells. If a lot of HER2 proteins are found, the cancer is called HER2 positive (HER2+). If no or very few HER2 proteins are found, the cancer is called HER2 negative (HER2-).

HER2- breast cancer is a type of cancer where cancer cells have no or very low levels of the HER2 protein. Having too much of the HER2 protein can help cancer cells grow quickly.

HER2+ breast cancer is a type of cancer where cancer cells include a protein called HER2. HER2 can cause cancer cells to grow quickly.

Lymph nodes are small, bean-shaped organs that are part of the body’s immune system. Lymph nodes filter substances and contain fluid with white blood cells that help the body fight infection and disease.

Metastases are cancer cells that have spread beyond the primary cancer site.

Metastatic breast cancer is cancer that has spread throughout the body through blood vessels or lymph nodes to a distant location, like the bones, lungs, liver, and brain. Metastatic breast cancer is also referred to as stage 4 breast cancer.

An initial diagnosis of stage 4 breast cancer is called de novo metastatic breast cancer.

Progesterone is a hormone that plays a role in menstruation and pregnancy. Progesterone will bind to the receptors inside the cancer cells, which may cause the cells to grow.

The stage of a cancer describes how much cancer is in the body. It helps determine how advanced the cancer is and how best to treat it.

Triple-negative breast cancer is a type of breast cancer with cells that do not include estrogen or progesterone receptors, and do not make much or any HER2 protein.