Inflammatory Pseudotumor-like Follicular Dendritic Cell Sarcoma Mimicking A Colonic Polyp: Two Case Reports and Literatures Review

Abstract BACKGROUND: Follicular dendritic cell (FDC) sarcoma is a neoplastic proliferation of spindled to ovoid cells showing morphological and immunophenotypic features of FDCs. Inflammatory pseudotumor-like follicular dendritic cell sarcoma（IPT-FDCS）involves almost exclusively in the liver and spleen and are consistently associated with Epstein-Barr virus (EBV).Rarely, it selectively involves the gastrointestinal tract in the form of a polypoid lesion.CASE SUMMARY: We report two cases of IPT-FDCS mimicking a colonic polyp that received high frequency electrocoagulation separately.The patients’main concern were whether to have chemotherapy or radiation after removal.After many consultations and literature review,The patients were treated by surgical resection, without adjuvant chemotherapy or radiation. Follow-up for 32 months showed no recurrence or metastasis.RESULTS: The neoplasms usually had well—defined borders，composed of the neoplastic spindled cells are dispersed within a prominent lymphoplasmacytic infiltrate. The nuclei usually show a vesicular chromatin pattern and small but distinct nucleoli. Immunohistochemically，tumor cells showed the expression of at least one of the FDC markers，including CD21,CD35, CD23 and D2-40，with scattered positive EBER in situ hybridization.CONCLUSION: IPT-FDCS could rarelly occur in the intestine with a polypoid appearance. Recognization of this disease could avoid being misdiagnosed as other common types of colonic polyposis. EBV-encoded mRNA (EBER) by in situ hybridization and FDC-related immunohistochemical markers plays an important role in differential diagnosis.