A 50‐year‐old Hispanic woman presented to the medical walk‐in clinic of a local community hospital complaining of shoulder pain. The problem had begun 9 months previously, and first manifested as dull right shoulder pain that developed after she carried a bag of groceries up one flight of stairs. A diagnosis of “muscle strain” and “arthritis” was made for which nonnarcotic analgesics were prescribed. The pain persisted, and 2 months later she was re‐evaluated and diagnosed with degenerative joint disease. An orthopedics consultation was sought for further evaluation. During this examination, she pointed out to the physician that she had a “lump in her shoulder,” but she was informed that this was of no consequence and that her complaints were due to arthritis. Roentgenograms of the right shoulder and thoracic spine were performed and determined to be within normal limits. Once again she attempted to control the pain with nonsteroidal anti‐inflammatory agents to no avail. Because the pain had become unbearable, she sought relief at the medical walk‐in clinic. Physical examination was remarkable for a solitary, skin‐colored, firm, deeply‐seated tumor measuring 3×4 cm located over the right posterior of the deltoid. The mass was exquisitely tender to palpation and was fixed to the underlying muscle. There was a full range of motion as well as good muscle strength of the shoulder, but movement of the arm in any direction was painful. The patient subsequently underwent a deep, partial excisional biopsy of the lesion, and a firm white tumor mass of about 3 × 3 cm in size was dissected away from the deltoid muscle. Although the majority of the tumor was excised, visible portions of the lesion were not removed because they were present deep within the bulk of the muscle. Histopathologic examination revealed a large, deeply‐seated poorly‐circumscribed fibrous proliferation containing areas in which there were numerous spindle cells arranged in fascicles ( Figs 1, 2, and 3). Neither cellular atypia nor mitotic figures were seen. The diagnosis of extra‐abdominal desmoid tumor was made. The patient subsequently underwent a wide re‐excision of the area and tolerated the procedure well, developing normal function of the arm following surgery, although there was slight persistent tenderness of the deltoid. Because of the known association of desmoid tumors with familial polyposis coli 1, a barium enema was performed. No colonic polyps were demonstrated. 1 Histopathology of desmoid tumor at scanning magnification. There is a large, poorly‐circumscribed, diffuse spindle cell proliferation that extends into the subcutis, muscle, and fascia (hematoxylin and eosin; original magnification, ×10) 2 At still higher magnification, abundant spindle cells in fascicles were appreciated and could be readily distinguished from collagen bundles. Note the elongated, wavy nuclei. No cellular atypia was seen (hematoxylin and eosin; original magnification, ×480) 3 At still higher magnification, abundant spindle cells in fascicles were...