Sudden soreness in the right arm may be caused by lung cancer, breast cancer and other cancers; it can also be caused by non-cancer factors, such as trauma, etc. The statement of four types of cancer is slightly absolute. According to anatomical factors, when lung cancer, breast cancer and other malignant tumors invade the nerves or lymph nodes or distant metastases occur, it usually leads to soreness in the right arm. However, it is mostly in the progressive stage of the disease, so it is often accompanied by symptoms of primary tumor at the same time. Lung cancer can have cough, hemoptysis, chest pain and other manifestations; breast cancer can have cellulite, lumps and other symptoms. In addition, non-cancer factors can also lead to sudden right arm pain, such as trauma, muscle strain, humeral epicondylitis, shoulder and neck muscle injury. Therefore, patients should go to the hospital for standardized examination in time after discomfort occurs, in order to treat the cause and avoid delaying the condition.