Breast Cancer Facts

April 10, 2025

This page was reviewed under our medical and editorial policy by Nikhila Kethireddy, M.D., assistant clinical professor, and Susan Yost, Ph.D., staff scientist, Department of Medical Oncology & Therapeutics Research, City of Hope^® Cancer Center Duarte

Breast cancer is a disease that begins in one or both breasts. It occurs mostly in women, although a small percentage of men are also diagnosed with the condition each year.

Learning the facts about breast cancer helps patients and their loved ones better understand the disease and take the next steps on their treatment journey.

What Is Breast Cancer?

Breast cancer is a disease in which breast tissue cells start growing abnormally and uncontrollably. It is the second most frequently diagnosed cancer among women in the United States, after skin cancer.

Breast Cancer Statistics

Breast cancer is among the most common cancers in the U.S. Following are several statistics about the disease.

• The average age at the time of breast cancer diagnosis is 62.
• About 1 in every 8 women will be diagnosed with breast cancer in her lifetime.
• Fewer than 1% of all breast cancer cases affect males.
• The average five-year relative survival rate for all breast cancers is 91.2%.
• Breast cancer accounts for about 1 in every 3 cancers affecting women.
• In the U.S., breast cancer rates are highest in North Carolina, Minnesota, Connecticut and Washington, D.C.
• Most women diagnosed with breast cancer don’t have a family history of the disease.
• The majority of breast cancers are diagnosed in the earlier stages.
• About 16% of breast cancer patients are diagnosed with the disease before age 50.

What Causes Breast Cancer?

Breast cancer develops when cells in the breast tissue begin to grow abnormally and out of control. As these unhealthy cells grow, this leads to the development of a tumor. These tumors may be noncancerous (benign) or cancerous (malignant). In most cases, why this happens is not known.

Cancer may begin in different parts of the breast. Most breast cancers start in the epithelial cells lining the lobules that produce milk and the ducts that transport milk from the lobules to the nipples. These breast cancers are known as carcinomas.

Though less common, breast cancer may also form in:

• Paget cells in the nipple region where the ducts transfer milk, which is called Paget’s disease of the breast
• Blood and lymph vessels, which is known as angiosarcoma
• Fat and connective tissue that surrounds the ducts and lobules of the breast

Doctors and surgeons use information about where breast cancer begins to help guide their treatment recommendations for each patient.

What Increases the Risk of Breast Cancer?

While the exact causes of breast cancer are not yet known, researchers have identified certain risk factors for the disease. Risk factors are things that increase the likelihood of getting breast cancer.

• Breast cancer risk factors may include:
• A personal or family history of the disease
• Increased lifetime exposure to estrogen, for instance, due to:
  • Early onset of menstruation (before age 12)
  • Late onset of menopause (after age 55)
  • Taking estrogen and progesterone after menopause
  • Never having given birth or first giving birth after age 30
• Having dense breast tissue
• Obesity
• Prior radiation therapy to the chest area
• Consuming alcohol, especially more than two drinks a day
• Being aged 55 and older (most invasive breast cancers are found in women in this age group)
• Race and ethnicity (white women are more likely to be diagnosed with breast cancer, but African American women are more likely to be diagnosed at a younger age, under 40, or to die from the disease)
• An inactive lifestyle, especially in women who have been through menopause
• Certain noncancerous breast conditions like simple cysts
• A previous breast cancer diagnosis, especially for younger women
• Birth control (taking oral contraceptives, and for about 10 years after stopping)

Is Breast Cancer Hereditary?

Sometimes breast cancer develops because of gene mutations (changes). While the majority of these changes occur after the person is born, a small number (about 10%) are hereditary. Hereditary means that the gene mutations are passed down from the parents to the child before the child is born. In these cases, breast cancer is hereditary.

The Breast Cancer Centers located in each City of Hope hospital focus on fast appointment scheduling and comprehensive medical exams to identify patient risk factors for the disease. Advanced diagnostic testing helps care teams provide an accurate diagnosis based on factors such as gene mutations and other biological findings linked to the condition’s development. For women and men diagnosed with breast cancer, an all-in-one medical care center offers therapeutic treatment and support services that center on whole-person care.