Why does breast cancer cause a breast lump?

Cancer cells can multiply in a confined area and change the structure of the surrounding tissue. This may create a firm area that feels different from the rest of the breast. Some masses are painless, while others cause discomfort or pulling. A lump can also arise from many non-cancerous conditions, so feeling one does not establish a diagnosis. Changes in size, shape, skin, or the nipple provide useful information for a clinical assessment.

Arrange an appointment for any new or persistent lump, even if it is not painful. The clinician may examine both breasts and armpits and recommend imaging or a tissue sample when needed. Note when you first noticed the change, whether it varies with your menstrual cycle, and any related nipple or skin changes.

Seek prompt assessment for a new lump with skin dimpling, nipple inversion, bloody discharge, swelling in the armpit, or a change that is progressing. Rapid breast swelling, marked redness, or feeling acutely unwell also needs timely medical review.

Ask which examination or imaging is appropriate, whether the lump needs sampling, and when you should expect the next result or follow-up appointment.