Histopathological Features and Immunophenotype of Primary Gastric Invasive Fibromatosis

Background: To investigate the histopathological characteristics, immunophenotype and differential diagnosis of primary gastric invasive fibromatosis. Methods: The clinical manifestations, histological morphology and immunophenotype of 4 cases of primary gastric invasive fibromatosis were observed and related literatures were reviewed. Results: Among the 4 patients, 2 were males and 2 were females, aged 28 and 47 years, respectively. The lesions were located in the stomach in 2 cases, the gastric antrum in 1 case and cardia in 1 case. Under the microscope, the tumor was located in the submucosa, growing infiltratingly, and infiltrating into the gastric wall muscularis, serous membrane and extraserous fatty tissue. Tumor cells were rich in cytoplasm, with unclear cell boundaries, long rod-shaped nuclei, deep chromatin, no atypia, and rare mitotic figures. The tumor tissue was composed of proliferating spindle-shaped fibroblasts and collagen fibers, and the cell morphology was relatively uniform, arranged in parallel bundles or staggered weaves. Tumor tissue invaded and destroyed smooth muscle, blood vessels, nerve tissue and adipose tissue of the gastric wall. Immunophenotype: positive expression of vimentin, β-catenin, SMA positive expression; CKpan, EMA, S-100 protein, desmin, CD99, Bcl-2, ALK, CD34, CD117, DOG1, hormone receptors were all negative; The cell proliferation index ki-67 positive cells were 3–5%. Conclusion: Primary invasive fibromatosis of the stomach is a relatively rare spindle cell tumor, which needs to be differentiated from tumors and pathological lesions such as inflammatory myofibroblastic tumor, plexiform mucinous fibroma, gastrointestinal stromal tumor, etc.