Breast Cancer Overview

The most common type of breast cancer is ductal carcinoma, which begins in the ducts of the breast, followed by lobular carcinoma, which begins in the lobules. Signs and symptoms of breast cancer may include pain in the breast; the appearance of a lump in the breast or armpit; discharge from the nipple; or swollen or red skin on the breast, nipple, or areola.¹

While breast cancer can occur in anyone, women are more likely to develop breast cancer than men; men make up only about 1% of breast cancer cases and deaths.² The risk factors for breast cancer include older age, a family history of breast cancer, dense breast tissue, obesity, alcohol intake, and prolonged exposure to estrogen (e.g., due to starting menstruation early or experiencing menopause later).¹ Certain variants in the BRCA1 and BRCA2 genes are also associated with a higher risk of some cancers, including breast and ovarian cancer.³

Breast cancer is commonly treated with surgery, though the type of surgery required varies depending on the location and size of the tumor and other factors. Radiation therapy, chemotherapy, targeted therapy, or hormone therapy may also be included as part of an effective treatment plan.²

The Sister Study is an ongoing study by the National Institute of Environmental Health Sciences (NIEHS) that is investigating the causes of breast cancer and the factors that affect health outcomes after a breast cancer diagnosis. This study, which has been running for over 20 years, has enrolled more than 50,000 women from the United States and Puerto Rico. Each participant has a sister who had breast cancer, which allows NIEHS researchers to study the potential risk factors for breast cancer among people with shared environments, genes, and life experiences. The Sister Study continues to track the health of these women through annual health updates and periodic questionnaires.⁴

The National Cancer Institute (NCI) also supports a number of research initiatives related to breast cancer, including those looking to improve current screening and treatment options.