A benign fibroblastic neoplasm composed of uniform spindle cells with abundant fibromyxoid stroma and a prominent network of innumerable branching, thin-walled blood vessels. It typically arises in the extremities, mainly the legs, frequently involving or adjacent to large joints such as the knee. Unusual anatomical locations include the back, abdominal wall, pelvic cavity, and breast. The tumors are often subcutaneous but may be intramuscular and deep. The lesion presents most often as a slow-growing painless mass. (WHO 2020) [from
NCI]