A mass in the arm may be a tumor, such as a lipoma of soft tissue origin, or another mass, such as a sebaceous cyst. It may also be a tumor of bone origin, such as osteochondroma or osteosarcoma. The doctor needs to make a preliminary judgment in conjunction with the physical examination, and you can go to the orthopedic department for an interview in time. If the mass is of soft tissue origin, ultrasound or magnetic resonance imaging can be performed. If the mass is considered to be of bony origin, local X-ray examination and, if necessary, CT and three-dimensional reconstruction can be improved and the corresponding treatment can be done according to the results of the examination. If the mass is benign, such as lipoma, sebaceous cyst or osteochondroma, it can be removed by local surgery for the purpose of cure. If malignant tumor is considered, treatment such as amputation is needed if necessary.