Definition

In cancer, a term used to describe the smaller groups that a type of cancer can be divided into, based on whether certain genetic changes or other biomarkers are present. For example, breast cancer can be broken down into several molecular subtypes based on whether the cancer cells have estrogen receptors (ER), progesterone receptors (PR), or HER2 on their surface. Knowing the molecular subtype of a cancer may help plan treatment, find out how well treatment is working, or make a prognosis.