Why does breast cancer cause an armpit lump?

Armpit Lump is a common presentation of Breast Cancer. Lymph vessels drain breast tissue toward lymph nodes in the armpit. If breast cancer cells enter those vessels, nearby nodes may react or become enlarged as disease travels through the lymphatic system. A lump may feel firm, fixed, tender, or painless, but its feel alone cannot establish the cause.

Many armpit lumps are linked to other processes, such as a local infection, skin inflammation, a blocked gland, or a temporary immune response. Breast tissue and the armpit should therefore be examined together. The clinician may check both sides, review breast or skin changes, and arrange ultrasound, mammography, or tissue sampling when appropriate.

Arrange a clinical examination for a new, persistent, enlarging, or unexplained armpit lump. Note when it appeared, whether it changes with illness or the menstrual cycle, and whether there is breast pain, nipple discharge, skin dimpling, redness, or a change in breast shape. Do not repeatedly squeeze or massage the area, as this can irritate the skin and make changes harder to assess.

Bring a list of medicines and any recent vaccinations, infections, injuries, breast procedures, or cancer treatments. If breast cancer is already diagnosed, report a new armpit change to the treating team so they can relate it to examinations and planned imaging.

Seek prompt medical advice for a rapidly enlarging lump, a hard or fixed area, persistent swelling, skin breakdown, marked redness or warmth, fever, unexplained weight change, or a new breast or nipple change. Urgent help is appropriate if swelling is accompanied by severe illness, breathing difficulty, or rapidly spreading redness. These features need assessment; they do not determine the diagnosis by themselves.

Ask whether the lump feels like a lymph node, what imaging is suitable, and whether a biopsy is needed. Ask how breast examination findings relate to the armpit and when you should return if the lump remains or changes.