What is Breast Cancer?

Breast anatomy
A closer look at the breast tissue.

Breast cancer is the most common cancer that occurs in women, with as many as one in eight women developing the disease during their lifetime. Breast cancer occurs when cells in breast tissue grow out of control, a situation called malignant.

The breast consists of about 15 to 20 sections called lobes, which have multiple smaller sections called lobules. These lobules end in tiny bulbs where milk is produced. Tiny tubes or ducts, leading to the nipple, connect the bulbs, lobules and lobes. Fibrous tissue and fat surround the lobes and all of this breast tissue rests on the muscle of the chest wall. The cells that line the ducts and lobules are the ones that become malignant.

What is "invasive" breast cancer?

Sometimes, cancer cells are found only inside the duct or lobule, called carcinoma in situ. In most cases, however, cancer cells have invaded through the wall of the duct or lobule, becoming invasive cancer. The cancer may be called invasive ductal cancer or invasive lobular cancer, identifying the cell type where it started. When breast cancer becomes invasive, the cells may also invade the breast’s lymph vessels, spreading to lymph nodes, such as those in the armpit, or invade the small blood vessels in the breast and and travel to other body areas.

Learn how breast cancer is diagnosed Types of breast cancer

Breast Cancer Info Sheet Thumbnail

Breast Cancer Info Sheet 

Roswell Park recommends women begin annual mammography screening at age 40.

Learn more
Breast Cancer Teen Info Sheet Thumbnail - 2023

Breast Cancer Info Sheet for Teens

Most breast lumps are not cancer, but they still need to be checked out.

Learn more
Breast Cancer Info sheet for Indigenous Women

Breast Cancer Info Sheet - Indigenous 

3 in 4 women with breast cancer have no family history of the disease.

Learn more