Calcifying fibrous tumor of the stomach: clinicopathologic and molecular study of seven cases with literature review and reappraisal of histogenesis.

Calcifying fibrous tumor (CFT) is a rare benign mesenchymal tumor composed of hyalinized fibrous tissue with interspersed bland fibroblastic spindled cells, scattered psammomatous, and/or dystrophic calcifications and variably prominent mononuclear inflammatory infiltrate. CFTs show a predilection for the abdominal cavity and soft tissue. To date, 6 gastric and 3 intestinal CFTs have been reported. We analyzed 7 gastric CFTs including 6 new cases. Patients were 4 men and 3 women with a mean age of 53 years (range, 40 to 77). Mean tumor size was 2.2 cm. Most tumors originated in the gastric body (6/7). Six were incidental findings at autopsy or during surgery for other diseases. One ulcerated tumor caused iron deficiency anemia and ulcer symptoms. Six tumors involved the muscularis propria with variable submucosal and subserosal extension and 1 arose within thickened muscularis mucosae adjacent to a mucosal invagination. Histology was typical with uniformly hypocellular vaguely storiform collagen, lymphoplasmacytic infiltrates, lymphoid aggregates and psammomatous, and dystrophic calcifications. Peritumoral lymphoid aggregates were seen in 3 cases. Adjacent muscle coat contained lymphoid aggregates with fiber degeneration (2), minute CFT-like foci (1), and calcifications (1). In none of the cases were there remnants of burnt-out GIST, inflammatory fibroid polyp, inflammatory myofibroblastic tumor, leiomyoma, schwannoma, or other specific lesion. All tumors were negative for CD117, S100, smooth muscle actin, desmin, ALK1, h-caldesmon, and PDGFRA. Two stained focally with CD34. Scattered IgG4-positive plasma cells were seen in 4 of 6 cases stained with this marker. All 5 tumors with available tissue for molecular analysis were wild-type for KIT and PDGFRA. Three patients had follow-up (range, 12 to 24 mo); none developed recurrence. Gastric CFTs are distinct from sclerosing GIST and other mesenchymal gut lesions and may represent a localized inflammatory fibrosclerosis in response to immune-mediated or other-type tissue injury affecting the muscularis propria. They differ from soft tissue CFTs by smaller size, older age at presentation and lack of recurrence, and from peritoneal CFTs by equal gender distribution, older age, and absent multifocal occurrence.