RÉSUMÉ
Membranous nephropathy (MN) is a common glomerular disease that is characterized by diffuse thickening of the glomerular basement membrane, and a common cause of nephrotic syndrome (NS). MN is often accompanied with malignant disease; The solid tumors are commonly associated with MN, whereas hematological malignancies are rarely found in patients with MN. A 68-year-old man with a history of diabetes mellitus visited a hospital with a chief complaint of general fatigue. He was previously not diagnosed with any complications of diabetes. Computed tomography revealed a pancreatic tumor, and the pathological findings of the biopsied tumor revealed the tumor was diffuse large B-cell lymphoma (DLBCL). Concurrently, he developed severe proteinuria, hypoalbuminemia, systemic edema and hyperlipidemia, consistent with the diagnosis of NS. The biopsied renal specimen revealed minute spike lesions of glomerular basement membrane, and abnormal lymphocytes infiltrated in the kidney interstitially. Anti-glomerular basement membrane antibody, proteinase-3-/myeloperoxidase antineutrophil cytoplasmic antibody and hepatitis B antigenemia, are absent in the patient. Serum anti-phospholipase A2 receptor (PLA2R) antibody (marker for primary MN) was not detected. A diagnosis of secondary MN induced by DLBCL was made. He received rituximab containing chemotherapy for DLBCL, resulting in amelioration of both DLBCL and MN. We report the rare case of a patient co-existing NS and DLBCL. DLBCL might be pathogenesis of NS; the findings are supported by the presence of MN, an underlying malignancy (DLBCL), and the lack of anti-PLA2R antibodies. Although further investigation is warranted, our case suggests that DLBCL is a possible cause of secondary MN.