Causes of Armpit Pain and Swollen Breast

The female breast and the armpit are related in 4 ways: by anatomic proximity; by lymphatic drainage; by blood vessels; by extension of breast tissue up into the armpit. Diseases that affect one may therefore affect the other. Some causes of swollen breast and armpit pain are cancerous, some are non-cancerous and all require urgent evaluation by a doctor.

Swollen breast and armpit pain should always be evaluated by a doctor (Image: Stockbyte/Stockbyte/Getty Images)

Inflammatory Breast Cancer

An unusual but very aggressive form of cancer, inflammatory breast cancer causes swelling and hardening of the breast and tenderness in the armpit due to lymph node invasion by the cancer. The skin over the breast may be reddened and thickened, and there is usually not a lump that can be felt. Mammography very often misses the diagnosis, which can be made by removing a sample of breast tissue for biopsy and microscopic examination.

Lactational Mastitis

Pain and swelling of the breast with tender reaction in the armpit lymph nodes occurs in approximately 10 percent of women who breastfeed, according to a report in the May 2005 issue of "Australian Family Physician." Treatment may include a change in breast feeding technique but not discontinuation of nursing. Antibiotics are sometimes required to cure mastitis. Mastitis may progress to breast abscess.

Breast Abscess

Abscesses in the breast may occur in women who are either lactating or not. The infection may originate in the skin -- an infected cyst for example -- or in the breast tissue. Pus may drain from the nipple. The swelling and tenderness over the abscess may be accompanied by tenderness of armpit lymph nodes, which are swollen and inflamed in response to the infection. Antibiotics and drainage of the abscess should relieve both the breast swelling and armpit pain. Failure to respond to appropriate treatment may indicate an underlying cancer.

Lymphoma of the Breast

Lymphoma is a form of cancer that may arise in virtually any part of the body. All tissues, including breast, contain elements of the lymphatic system that may turn cancerous. When lymphoma arises in the breast it may cause swelling of the breast and cancerous enlargement and discomfort in the armpit lymph nodes. Removal of the breast is not necessary, and treatment consists of radiation and chemotherapy.