What is breast lump? A breast lump is a swelling, outgrowth, or protrusion in the breast. Both women and men have breast tissue. This normal tissue may respond to changes in hormone levels, leading to breast lumps. Lumps in the breast may come and go depending on hormone levels. Painless breast lumps can signal both benign (noncancerous) and malignant (cancerous) tumors of the breast. A new breast lump along with a lump under the armpit can be a sign of breast cancer that has reached a lymph node. Infection is another possible cause. A painful lump in the breast is most often associated with hormonal changes. Breast lumps can occur at any age in women and men. In adult women, lumps are most often caused by changes in the breast tissue related to hormonal shifts. These are called fibrocystic changes. Fibroadenomas (a type of benign tumor), cysts, and damage to the fatty tissue are other reasons for breast lumps in adult women. Breast infection (mastitis) or a small growth in the milk duct (intraductal papilloma) can also result in a breast lump. The majority of breast lumps are benign, particularly in women under age 40. Breast enlargement in men is called gynecomastia. This swelling of the breast tissue occurs most often in boys at mid-puberty. Tender lumps develop beneath one or both nipples in response to hormonal changes. These lumps generally disappear within a year. Infants may experience a breast lump because of estrogen they received from the mother’s bloodstream. Once the estrogen clears from the infant’s body, the lump will usually go away. Right before puberty, young girls develop lumps called breast buds. This tissue may be temporarily tender as girls start the early stages of puberty. In some instances, breast lumps can be associated with breast cancer. A painless but firm lump with irregular edges is a sign of a potentially cancerous breast lump. Seek prompt medical care if your breast lump is persistent or causes you concern.