Breast cancer is a type of cancer that starts in the breasts and can spread to the rest of the body through the blood or lymphatic systems.
There are many different types of breast cancer determined by the specific affected cells in the breast. Most breast cancers are carcinomas. The most common breast cancers such as ductal carcinoma in situ (DCIS) and invasive carcinoma are adenocarcinomas, since the cancers start in the gland cells in the milk ducts or the lobules.
Breast cancers can also be classified by the presence or absence of proteins or genes such as estrogen receptors, progesterone receptors, and the HER2 gene or protein. Classification can ifluenca prognosis and treatment plans.
Approximately 1 in 10 breast cancers are associated with known inherited genetic variants. Many of these genes have not yet been discovered. Most breast cancers (about 90%) develop from acquired genetic variation that occurs independent of inheritence and many have not yet been identified.
