Transformation of Parotid Gland Follicular Lymphoma to Diffuse Large B-Cell Lymphoma with Gastric Relapse and Perforation: A Case Report.

OBJECTIVE: Follicular lymphoma (FL) is an indolent non-Hodgkin lymphoma with rare parotid gland involvement. Histological transformation to diffuse large B-cell lymphoma (DLBCL) manifesting as gastric relapse complicated by rupture and perforation is extremely rare and clinically challenging. This case report aims to clarify its clinical characteristics, treatment strategies and prognostic significance. CASE REPORT: A 60-year-old male was diagnosed with grade 1 FL of the bilateral parotid glands in 2014 and discontinued regular follow-up thereafter. In December 2025, he was presented with recurrent chest pain, anemia and melena. Gastroscopy and histopathology confirmed DLBCL of the gastric lesser curvature, Ann Arbor stage IIIB. The patient refused chemotherapy and was discharged. In February 2026, he was readmitted due to syncope and progressive hematochezia. Abdominal imaging suggested gastric lymphoma rupture and suspected perforation. He received palliative distal subtotal gastrectomy, and postoperative pathology verified DLBCL of the distal stomach. Subsequently, he was treated with Polatuzumab vedotin combined with Rituximab and CEP regimen, and is currently in stable condition. CONCLUSION: This rare case emphasizes that long-term regular follow-up is essential for patients with parotid FL. Emergency surgery is a life-saving intervention for transformed DLBCL with gastric rupture and perforation. Further large-sample studies are needed to optimize the surveillance and treatment protocols for this rare condition.