You may ask, “What is the relationship between armpit or shoulder discomfort and breast? Some benign and malignant breast diseases are often accompanied by pain and discomfort in the armpit or back of the shoulder, and in some cases, there is no obvious discomfort in the breast, but only pain and discomfort in the armpit or back of the shoulder. It is because they do not know this that many patients always think that their underarm or back pain and discomfort is caused by frozen shoulder or other problems, without thinking that it may be caused by breast disease, and in some cases, the examination and treatment is delayed because of this. So, why do breast lesions affect the armpits or back of the shoulder? When does breast lesions cause pain and discomfort in the armpits or back of the shoulders? As we mentioned earlier, the vascular supply, lymphatic drainage and nerve distribution of the breasts determine that breast lesions can sometimes affect the nearby back of the shoulder and the ipsilateral armpit. For example, in acute infectious diseases of the breast, the inflammation may reach the ipsilateral axillary lymph nodes through the lymphatic vessels, resulting in swollen and painful lymph nodes; in hyperplastic diseases of the breast, the pain caused by the cyclic congestion and edema of the glands and interstitium may reach the ipsilateral chest and shoulder back through nerve reflexes, so it often manifests as breast swelling and pain radiating to the shoulder back; in malignant tumors of the breast, the initial metastasis is often The initial metastasis of malignant tumor of the breast is often to the ipsilateral axilla via lymphatic metastasis, and sometimes even the primary tumor of the breast is very small; the lymphatic metastasis has already occurred in the axilla when the breast lump cannot be palpated clinically. Therefore, we remind our patients and specialists not to forget that there is still a possibility of breast disease in cases where non-breast symptoms are the main complaint.