Breast Cancer

Introduction

Approximately 246,000 women in the United States, or 1 in 8, are diagnosed with breast cancer each year. Breast cancer occurs when breast cells grow abnormally and invade either nearby or distant tissues. It is the second most common cancer among U.S. women, behind skin cancer.

Signs of breast cancer may include a lump in the breast, a change in breast shape, dimpling of the skin, fluid coming from the nipple, or a red scaly patch of skin on the breast.

Breast cancer is more common in older women, and rarely occurs in men. In the US, white women are most likely to be diagnosed with breast cancer, but African-American women are most likely to die from the disease, according to the American Cancer Society.

What causes breast cancer?

NIEHS-funded research has clearly shown that breast cancer is caused by a combination of genetic, hormonal, and environmental risk factors.

But approximately 85% of breast cancers occur in women who have no family history of breast cancer, suggesting the importance of environmental factors. Since environmental factors may be identified and modified, NIEHS scientists and other experts in the field believe that prevention strategies are the best way to stop breast cancer before it starts.

Some environmental factors that have been consistently associated with increased breast cancer risk include:

• Smoking
• Alcohol
• Exposure to ionizing radiation
• Use of combination hormone therapy products
• Being overweight or obese, especially after menopause
• Taking diethylstilbestrol (DES), a synthetic estrogen given to pregnant women in the 1940’s to 1971 to prevent miscarriages or premature deliveries

Research also shows that more physical activity is linked to decreased breast cancer risk.

You can estimate your current risk for breast cancer using an online tool developed by NIEHS grantees.