Plexiform fibromyxoma of the stomach: a clinicopathological study of 10 cases

Plexiform fibromyxoma (PF) is a unique mesenchymal tumor of the stomach. The molecular characteristics of these tumors remain unclear. Here, we report 10 cases of PF with clinicopathological features and molecular features in detail. The patients ranged in age from 26 to 72 years (mean, 49 y) and most commonly presented with abdominal pain and distension, black stool, and anemia. Eight tumors were located at the antrum while two in the fundus of stomach. Histologically, tumor cells exhibited a plexiform growth pattern with multiple nodules in the muscularis propria of stomach wall and infiltrative borders. Immunohistochemically, all tumors were strongly positive for vimentin and smooth muscle actin (SMA), some were staining for CD10 (5/10), desmin (5/10), H-caldesmon (6/10) and progesterone receptor (PR, 6/10), however, CD34, S-100, Estrogen Receptor (ER), ALK, CD117 and DOG-1 were all negative in our cases. The glioma-associated oncogene homologue 1 (GLI1) gene translocation was detected in eight cases by FISH with three positive and five negative. Mutation analyses of C-KIT and platelet-derived growth factor receptor alpha (PDGFRA) genes were performed on five cases and all of which were wild-type for mutation. Our follow-up indicated that all of the patients made an uneventful recovery at 24 to 95 months after diagnosis. In summary, the distinctively histological features and immunohistochemical positivity of SMA, CD10 and PR can help differentiate PF from other gastrointestinal mesenchymal tumors. GLI1 gene translocation offers an additional molecular instrument for the diagnosis. The expression of PR and the existence of GLI1 gene translocation in PF highlights of our article.