Tumor on the outer side of the arm is mostly seen in benign tumors, but may also be malignant tumors, dynamic observation or surgical treatment can be taken. Lateral arm tumor is more commonly seen as lipoma or sebaceous cyst, which belongs to benign lesions. If the tumor size is relatively small and does not give rise to obvious clinical symptoms, it generally does not need special treatment, and dynamic observation should be paid attention to, and generally review once in 3-6 months. If the lipoma or sebaceous cyst is relatively large, it can be removed by surgical treatment if necessary. There is also the possibility of malignant tumors, after surgical treatment, depending on the condition may also need to take further chemotherapy, radiotherapy and so on. If a tumor grows on the outside of the arm, accompanied by obvious discomfort symptoms, you should go to the hospital in time to find out the cause of the tumor and then carry out targeted treatment.