Breast Cancer and NIH Women's Health Research

Signs, Symptoms, and Risk Factors

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

Diagnosis and Treatment

Breast cancer is diagnosed using a combination of clinical evaluation and imaging tests. Depending on a person's symptoms and medical history, doctors may recommend a diagnostic mammogram, breast ultrasound, or magnetic resonance imaging (MRI) scan to evaluate suspicious findings. If an abnormal area is detected, a biopsy is performed to remove cells or tissue for examination under a microscope. A biopsy is the only definitive way to diagnose breast cancer.^{4 , 5}

Breast cancer is commonly treated with surgery, although 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

Ongoing Research

Researchers continue to study how breast cancer risk that is associated with menopausal hormone therapy varies by hormone formulation, route of administration, dose, duration of use, and individual patient characteristics. Recent studies have also examined whether newer regimens, including transdermal estrogen and micronized progesterone, may have different risk profiles than older hormone therapies.^{6 , 7} Other studies are evaluating targeted treatments, including antibody-drug conjugates, for cancers that have stopped responding to hormone therapy.⁸ Researchers are also investigating how environmental exposures, such as air pollution and chemicals in some personal care products, may affect breast cancer risk in racially and ethnically diverse populations.^{9 , 10}

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.¹¹

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.