A hard lump under the armpit is seen in these cases: the first one, sebaceous cyst or subcutaneous lipoma, is a very common benign tumor that can occur in everyone. If the patient has significant pain, discomfort, or if it affects daily life and work, surgical removal under local anesthesia can be considered and is very simple. The second type of parametrium is a congenital developmental abnormality, which is caused by the degeneration of the breast tissue during the embryonic period. In some cases, the symptoms of mastopexy are also associated with mastopexy. If you have recurrent mastopexy, you may consider removing it. Because of the possibility of malignancy, surgery should be performed early and routine pathological examination should be performed after surgery. Thirdly, there are also some patients who have metastasis of axillary lymph nodes due to malignant tumors of the breast, which manifest as hard lumps in the armpit and require active treatment of the primary disease.