A hard lump in the armpit, or a swelling in the armpit, can be due to a variety of causes, the most common of which is an enlarged axillary lymph node. There are many reasons for this: for example, after a traumatic injury or in patients with breast enlargement, the axillary lymph nodes may be enlarged, swollen, or even painful. In the case of malignant tumors of the breast, metastasis of the axillary lymph nodes can easily occur, as well as hard lumps in the armpit and obvious pain, and even fused hard lumps in advanced cases, accompanied by abnormal changes in the local skin. If necessary, surgery is required to remove the parametrial breast.