Small lump on the side of the breast: what to know

The outer breast blends into tissue toward the armpit, where lymph nodes, skin glands and muscle also sit. A cyst, fibroadenoma, inflamed skin gland, swollen lymph node or normal rib and muscle contour can feel like a small lump. Breast cancer commonly presents as a new breast lump, but a side-of-breast lump does not identify its cause by itself.

Tell the clinician whether the lump is in the breast, the fold beneath the arm or the chest wall, and whether it changes with your menstrual cycle or arm movement. Examination can help locate it; ultrasound or other imaging may be used when needed.

Arrange an appointment for a new, persistent or unexplained lump. Before you go, record when it appeared, any recent vaccination, infection, injury, shaving irritation or breast changes, and whether it is tender. Avoid repeatedly pressing it. Wear clothing that allows comfortable examination and mention pregnancy, breastfeeding, hormone medicines or a personal family history that may affect the assessment.

Seek prompt assessment for a lump that is hard, fixed, enlarging or associated with skin dimpling, nipple change, bloody discharge or a lump in the armpit. Redness, warmth, fever or rapidly increasing pain may indicate infection and should be reviewed promptly. Get urgent help if you feel severely unwell or the redness is spreading quickly.

Ask exactly where the lump appears to be, whether it feels like breast or underarm tissue, what imaging is appropriate and what follow-up is needed. Ask when to return if it changes, becomes painful or remains after your next period.