Breast Cancer Facts

Breast cancer is a malignant (cancerous) tumor that forms in the tissues of one or both breasts. Although breast cancer primarily affects women, it can also occur in children and men. For the most part, the content in this section describes breast cancer in women.

According to the American Cancer Society (ACS), in the United States breast cancer is the second most common cancer in women (after skin cancer) and the second leading cause of cancer death in women (after lung cancer). ACS estimated that 261,100 new cases of breast cancer (in situ and invasive cancers) were diagnosed among women in this country in 2010. Breast cancer affects one in eight women. It can be a highly curable disease if detected and treated early.

Breast Cancer Symptoms

Get familiar with common warning signs of breast cancer.

Screening & Diagnosis

Learn about screening tests for woman with no symptoms, plus diagnostic tests used when breast cancer is suspected.

Types and Grades of Breast Cancer

Here’s an overview of some of the more common types of breast cancer—and what is meant by “grade,” “hormone-receptor positive,” and “HER2 positive.”

Stages of Breast Cancer

Find out how a cancer is classified based on its size and how far it’s spread—key factors that influence treatment.

Risk Factors

See who is at greatest risk for breast cancer, and estimate your risk level.

Questions & Answers

Your questions about breast cancer answered—topics from digital mammography and hormone replacement therapy to tamoxifen and aromatase inhibitors.