Breast cancer is a disease that starts in the breast with a malignant tumor. A malignant tumor is a mass of cells that grow out of control. The cancerous cells can also metastasize, or move to other tissues or parts of the body.

The cancer can develop in any of the three types of breast tissue: lobules, ducts, and connective tissue.

Most cancer begins in the lobules (the milk-producing glands), or in the ducts, along which milk travels to the nipple. But tumors can also develop in the fibrous and fatty connective tissue that surrounds the lobules and ducts.

Several different types of breast cancer exist. The type of breast cancer and its stage, or how far it has grown, determine the treatment for it.

Breast cancer that spreads into normal tissue is called invasive breast cancer. Noninvasive breast cancer stays within the breast lobule or duct.

Breast Cancer Is a Common Disease — but Numbers Are Going Down

Breast cancer makes up about 30 percent of new cancer diagnoses in women and 15 percent of all new cancer diagnoses each year. However, the rate of breast cancer cases began dropping in the year 2000 and have continued declining since.

About one in eight women (about 12.4 percent of all women) will be diagnosed with invasive breast cancer at some point in their lives. Breast cancer can occur in anyone with breast tissue, but it’s much rarer in men than in women.

Finding Your Best Treatment Team

After receiving a diagnosis, you will have several decisions to make about the health care providers who will handle your treatment.

Cancer treatment usually involves a team of people, such as a surgeon, a medical oncologist, a nurse practitioner, a counselor, a patient navigator, and specialists associated with your cancer type.

Factors to consider in choosing your oncologist and treatment team are their expertise in your cancer type, what your insurance will cover, your ability to travel to and from appointments and procedures, and recommendations from others.

Even after you have a treatment team, it is a good idea to look for another oncologist to get a second opinion on your diagnosis and treatment options. It is acceptable and sometimes common to change doctors during your treatment if needed.

Article Written By Tara Haelle
Medically Reviewed By Krystal Cascetta, MD