Breast cancer is the leading cause of cancer-associated mortality in women worldwide and is the most common cause of cancer in the United States and the second most common cancer worldwide (after lung cancer). The incidence of female breast cancer is about 124.7 per 100 000 patients. Male breast cancer is much less prevalent. Breast cancer is rarely diagnosed in childhood or adolescence, and the incidence increases with age.

Since the average lifetime risk of the diagnosis of breast cancer is around 12.4%, the US Preventative Services Task Force (USPSTF) recommends screening every other year for average-risk individuals beginning at age 40. In individuals older than 75 years, screening may be pursued after discussion with their physician, weighing the benefits and risks. Screening is done with mammography. Women with dense breasts may require additional imaging, such as ultrasound or MRI.

Risk factors associated with breast cancer include genetic predisposition (eg, BRCA1, BRCA2, PTEN, TP53 mutations; very large studies show that mutations in dozens of genes may be associated with increased breast cancer risk), increasing age, Northern European descent, obesity in postmenopausal women, family history of breast / ovarian / peritoneal cancer, and personal history of ovarian, breast, or peritoneal cancer. In the general population, BRCA1 and BRCA2 mutations occur in an estimated 1 in 300-500 women and account for 5%-10% of breast cancer cases. Individuals with BRCA mutations require a personalized cancer screening plan developed with their physician.

In countries with established screening programs, the majority of breast cancers present due to abnormal mammogram findings. Despite this, almost 1 in 6 women who are diagnosed with breast cancer present with a breast mass not detected by mammogram, and slightly fewer than 1 in 3 present with a mass that developed in the interval between mammograms.

Breast cancer typically presents as a painless, immobile breast lump or abnormality found on mammography. In more advanced cases, it can present with bloody nipple discharge, axillary lymphadenopathy, thickening and erythema of the skin (peau d'orange appearance), and metastatic disease commonly found in bones, liver, and lungs. Metastasis to the bone marrow may be associated with anemia. Ductal carcinoma in situ (DCIS) is considered a precursor lesion and is confined to breast ducts and lobules.

The diagnosis of breast cancer is made based on malignant-appearing cells found on biopsy. The treatment of breast cancer varies according to stage of disease as well as the histologic and genetic subtype of the malignancy. Common histologic subtypes include infiltrating ductal carcinoma, infiltrating lobular carcinoma, and mixed ductal / lobular carcinoma. Tumor expression of estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor 2 (HER2) is used to predict outcomes and guide treatment. The incidence of triple-negative cancers (ie, ER-, PR- and HER2-) is twice as high in Black women compared with White women (24.2 versus 12.3 cases per 100 000 women).

Related topic: cutaneous presentations of breast cancer