Overview

What Is Breast Cancer?

Breast cancer begins when normal cells in the breast change and grow. They form a mass called a tumor. A tumor can be benign (noncancerous) or malignant (cancerous, and it can spread to other parts of the body).
  • Breast cancer is the most common cancer in women, after skin cancer.
  • In the U.S., it’s the second most common cause of death from cancer in women, after lung cancer.
  • Men can also develop breast cancer, but it's rare. Less than 1 out of 100 breast cancer cases occur in males.

How Breast Cancer Develops

The breast is mostly made up of fatty tissue. Within this tissue is a network of lobes, which are made up of tiny, tube-like structures called lobules. Lobules contain milk glands.

Tiny ducts connect the glands, lobules and lobes. They carry milk from the lobes to the nipple, located in the middle of the areola. The areola is the darker area that surrounds the nipple.

Blood and lymph vessels run throughout the breast. Blood nourishes the cells, and the lymph system drains bodily waste products. The lymph vessels connect to lymph nodes, which are tiny, bean-shaped organs that normally help fight infection.

About 9 out of 10 breast cancer cases start in the ducts or lobes. Almost 3 out of 4 breast cancers begin in the cells lining the milk ducts. These cancers are called ductal carcinomas. Cancer that begins in the lobules is called lobular carcinoma.
  • If the cancer has spread outside of the duct and into the surrounding tissue, it is called invasive or infiltrating ductal carcinoma.
  • If the cancer has spread outside of the lobule, it is called invasive or infiltrating lobular carcinoma.
  • Cancer that has not spread is called in situ, which means, “in place.”

Other Types of Breast Cancer

Less common breast cancers include:
  • Medullary
  • Mucinous
  • Tubular
  • Metaplastic
  • Papillary
Additionally:
  • Inflammatory breast cancer is a faster-growing type of cancer. Up to 5 out of 100 breast cancers are inflammatory. It may be misdiagnosed as a breast infection because it can cause swelling in the breast and redness of breast skin.
  • is a type of “in place” (in situ) cancer that can start in the ducts of the nipple. The skin often appears scaly and may be itchy.