Reticulum cell sarcoma (primary reticulum-cell sarcoma of bone) is a primary bone tumor originating from the bone marrow or cancellous bone. Although its morphology is consistent with diffuse lymphoma-type reticulum cell sarcoma, they are two different diseases. Reticulum cell sarcoma is a localized, isolated bone lesion, accounting for 5% of primary malignant tumors. The age of onset is mostly between 20 and 30 years old, and it is rare in children. 50% of the cases are under 40 years old, and there are also cases over 40 years old. The male-to-female ratio is 2:1. Any bone can be invaded, but the most common ones are the femur, tibia and humerus. One-third occur around the knee joint. The humerus accounts for about 9%, and flat bones such as the hip, scapula and spine also often occur.