Abstract

Background: The distribution and reactivity pattern of neural cell adhesion molecule (NCAM/CD56) in gastrointestinal stromal tumours (GISTs) and their mesenchymal mimics have not been investigated in the KIT era.

Methods: 275 histologically and immunohistochemically well characterised primary and metastatic intra-abdominal mesenchymal lesions were analysed by conventional immunohistochemistry, with emphasis on GIST and GI smooth muscle neoplasms.

Results: CD56 expression was seen in 18/21 (86%), 4/5 (80%), 26/34 (76%), and 32/168 (19%) of primary GI leiomyomas, schwannomas, leiomyosarcomas, and GISTs, respectively. Reactivity in GISTs was mostly focal. Of 6% strongly staining GISTs, 71% were either malignant clinically or assigned a high risk prognostic group. CD56 expression in GISTs varied greatly with histological type (seen in 50% and 7% of epithelioid and spindled GISTs, respectively) and anatomical site (in 33%, 10%, 1%, and 0% of rectal, gastric, small intestinal and oesophageal GISTs, respectively). A variable, but inconsistent expression was seen in miscellaneous lesions including dedifferentiated liposarcoma, abdominopelvic PEComa, myo/fibroblastic sarcoma and malignant fibrous histiocytoma. Mesenteric fibromatoses, angiosarcoma/Kaposi sarcoma, reactive tumefactive fibrogenic lesions and 12/13 primary anorectal and oesophageal melanomas were negative.

Conclusion: Results confirmed the ubiquity and non-specificity of CD56 as a neurogenic marker. Except for a subset of epithelioid gastric and high-grade rectal GISTs, CD56 expression is rare in GISTs, contrasting with true leiomyomatous and neurogenic neoplasms. CD56 plays a limited role in the differential diagnosis of GIST. Its potential role as a marker of adverse outcome in GISTs remains to be further investigated.