After breast cancer breast-conserving surgery, local hardness of breast is mainly seen in scar tissue in breast, tissue fibrosis caused by postoperative radiotherapy, recurrence of breast cancer and so on. 1. Scar tissue: after breast cancer breast-conserving surgery, the surgical site in the breast will gradually repair by itself, formed by collagen fiber connective tissue, which is harder than the surrounding tissues, so the breast will be hard locally. 2. Tissue fibrosis caused by postoperative radiotherapy: after breast cancer breast-conserving surgery, it is necessary to give postoperative radiotherapy and other adjuvant treatments. Local radiotherapy can lead to local microcirculation obstacle in the breast, which will cause local cell degeneration and formation of hard lumps. 3. Breast cancer recurrence: the diseased tissue of breast cancer breast-conserving surgery may not be removed completely, so it is more likely to have recurrence after the surgery. In the case of breast cancer recurrence, the local breast cancer lump may appear again and become hard locally. Localized hardness of breast after breast cancer breast-conserving surgery may also be caused by other reasons such as inflammation, and it is recommended that patients go to hospital in time to improve the auxiliary examinations so as to clarify the cause of the disease and actively treat it.