Membranous Nephropathy with Concurrent THSD7A Staining in Kidney and Prostate Cancer Biopsies: A Case Report

Introduction: Thrombospondin type-1 domain-containing 7A (THSD7A)-associated membranous nephropathy (MN) is reported to be cancer-associated in about 13% of cases. Prostate cancer is among the more commonly reported associations. However, while concurrent THSD7A staining in kidney and tumor tissues has been described in cancers such as lung, colon, and gallbladder, it has not been reported in prostate cancer. Case Description: A 64-year-old man presented with 3 months of edema, proteinuria 4.7 g/day, and hypoalbuminemia 1.4 g/dL. Secondary work-up was unremarkable except for positive serum anti-THSD7A. Kidney biopsy confirmed MN. While malignancy screening was underway, worsening edema and proteinuria up to 12 g/day prompted the start of prednisolone and cyclosporine. High-risk prostate cancer was diagnosed 5 weeks later via transrectal ultrasound-guided biopsy. To assess THSD7A’s source and role, THSD7A immunohistochemistry (IHC) was performed. It showed global positive staining of moderate intensity along glomerular basement membrane in >50% of viable glomeruli, and focal positive luminal staining in the neoplastic glands of prostatic adenocarcinoma. Degarelix was started and steroids tapered. At 3 months, serum prostate-specific antigen fell from 20.6 to 0.6 µg/L, proteinuria decreased to 3.4 g/day, and serum albumin improved to 2.4 g/dL. Discussion: To our knowledge, this is the first reported case of concurrent THSD7A staining in kidney and prostate cancer tissues in MN. It suggests prostate cancer as a potential antigen source contributing to anti-THSD7A formation and MN. IHC aided diagnosis and treatment. Malignancy screening is important in THSD7A-associated MN.Kidney THSD7A-IHC, x200Prostate THSD7A-IHC, x200