Clinical improvement of membranous nephropathy after endoscopic resection of double early gastrointestinal cancers.

A-52-year-old man presented to our hospital with nephrotic syndrome caused by membranous nephropathy. Early gastric adenocarcinoma confined to the submucosa, and well-differentiated adenocarcinoma in a sigmoid adenoma were detected by screening endoscopy. Two years after complete endoscopic resection of these tumors, the estimated 24-h urinary protein excretion decreased, and serum total protein and albumin returned to their normal levels although he had no immunosuppressive therapy. Thus, this case was considered to be a case of secondary membranous nephropathy to cancer, although whether the pathogenesis was due to circulating or in situ immune complexes is unknown. The suspected antigen component of this immune complex can include carcinoembryonic antigen (CEA) and carbohydrate antigen 19-9 (CA19-9). In our patient, however, serum CEA and CA19-9 were within normal values during the clinical course, and detected cancers were early stage and very small. Recently, the existence of anti-mucin 1 (MUC1) antibodies before carcinogenesis and their usefulness for early detection of cancer were reported. We tried to stain tumors and glomeruli for MUC1 but, although we had positive findings in both tumors but not in glomeruli, the role of MUC1 in the pathogenesis of membranous nephropathy is unknown. To the best of our knowledge, paraneoplastic nephrosis caused by double early cancers expressing MUC1 in the gastrointestinal tract has not been previously reported.