[Clinicopathologic features of gastric plexiform fibromyxoma]

Objective: To analyse the clinicopathologic features of gastric plexiform fibromyxoma (PF) including diagnosis, differential diagnosis, immunohistochemistry and molecular pathology. Methods: Eight cases of PF were collected from June 2006 to June 2017 at the Second Affiliated Hospital of Zhengzhou University and the First Affiliated Hospital of Zhengzhou University. The clinicopathologic findings of eight cases of PF were retrospectively analyzed, and immunohistochemistry (EnVision method) and molecular detection of glioma-associated oncogene homologue 1 (GLI1) gene translocation were performed. All cases were histologically reviewed with immunohistochemical staining for smooth muscle actin (SMA), CD10, CD117, DOG1, CD34, ER, PR, ALK and S-100. Fluorescence in situ hybridization (FISH) was used to detect the GLI1 gene translocation, and mutation of CKIT exons 9, 11, 13 and 17; and PDGFRA exons 12, 14 and 18 were identified by Sanger sequencing in four cases. Relevant literature was reviewed. Results: The study included four men and four women, age ranged from 26 to 72 years (mean 51 years). Histologically, the tumors were rich in small thin-walled blood vessels and myxoid matrix, and exhibited multiple nodular growth pattern in the gastric wall. The tumor cells were bland, spindled or oval. Immunohistochemically, all cases strongly expressed vimentin and SMA, and some expressed CD10 (4/8), desmin (3/8), H-caldesmon (5/8) and PR (5/8), but were negative for CD34, S-100, ER, ALK, CD117 and DOG1. The GLI1 gene translocation detection was performed in eight cases by FISH with three positive cases and five negative cases. Mutation analyses for exons 9, 11, 13, and 17 of CKIT genes and exons 12, 14, and 18 of the PDGFRA genes were performed and the tumors all of four tested cases were wild-type. Seven patients were followed up (ranged from 24 to 95 months, mean 50 months) after diagnosis and none of the patients had recurrence or metastasis. Conclusions: PF is a rare novel mesenchymal tumor of the stomach. Its distinct clinicopathologic features and immunohistochemical positivity for SMA, CD10 and PR can help differentiating this entity from other gastrointestinal mesenchymal tumors. FISH detection of GLI1 gene translocation offers an additional molecular diagnostic marker for the diagnosis.