Breast cancer can either be in situ or invasive. All carcinomas in situ are noninvasive histologic types but have the potential to become invasive. Close to 80% of invasive carcinomas are ductal adenocarcinomas; 8–15% are infiltrating lobular carcinomas.

Breast cancer is the most frequently diagnosed cancer in women in the US and the second most frequent cause of cancer death (43,300 deaths per year).

Lifetime risk of developing breast cancer is often quoted to be 1 in 7 for women, but this statistic is misleading in that one-third is in women over age 75. Therefore, a 40-year-old woman with no other risk factors shouldn't think she has a 1 in 7 chance for developing breast cancer in the next 10 years. The chances of developing breast cancer by age 50 is 1 in 50. Less than 1% of all breast cancer cases occur in men.

Etiology is complex and there are multiple risk factors. Significant genetics influence is implicated in 5–10%, including the genes BRCA1 and BRCA2; an additional 10–15% of breast cancers have moderate genetic risk factors (i.e. multiple minor genes).

All patients with a discrete mass, nipple changes, or persistent mastalgia should be referred to a breast specialist.

Mammography screening has increased the diagnosis of breast cancers; 45% of breast cancers can be seen on mammography before they are palpable.

Treatment may require surgery, radiotherapy, chemotherapy, and hormonal therapy. Palliative care enhances quality of life.