Primary lung follicular dendritic cell sarcoma with rare paraneoplastic pemphigus：a case report

Background: follicular dendritic cell sarcoma is a rare soft tissue tumor. The incidence is even lower when the lung is the primary site and combined paraneoplastic pemphigus. The purpose of this report is to present the clinicopathological features of this neoplasm in a 29-year-old man. In our case, this tumor caused the patient to develop a paraneoplastic syndrome as well as systemic symptoms. Although local excision of the primary tumor is the treatment of choice, patient required long-term administration of hormones and immunosuppressants. This case provides a new understanding of FDCS with paraneoplastic syndrome. Case presentation: A 29-year-old man was admitted to our hospital with “intermittent cough and sputum for more than 8 months, oral mucosal erosion for 6 months”. The patient had systemic symptoms, including coughing, genital and eye corneal ulcer, photophobia, decreased vision, multiple oral pseudomembranes , local chickenpox and multiple red papules all over the body. The patient underwent thoracoscopic lobectomy and regional lymphadenectomy and pathological biopsy of oral pseudomembranes was performed. Histopathological findings revealed Primary lung mucosal cell sarcoma with paraneoplastic pemphigus, and postoperatively, patient required long-term administration of hormones and immunosuppressants. Conclusion: Follicular dendritic cell sarcoma (FDCS) is a rare tumor associated with paraneoplastic pemphigus, which derived from follicular dendritic cells. Paraneoplastic pemphigus (PNP) is always associated with neoplasm, including gastric adenocarcinoma and lung cancer. the vast majority of FDCS occurs in lymph nodes, so extranodal FDCS cases remain challenging to diagnose, particularly when it occurs in an uncommon site or the histopathologic morphology is atypical. This article emphasizes the rarity of lung extranodal FDCS, and increases awareness of FDCS with paraneoplastic syndromes.