Malignancy-Associated Membranous Nephropathy with Positive Anti-PLA2R Autoantibodies: Coincidence or Connection

Membranous nephropathy (MN) is currently classified as either primary − often associated with positive anti-phospholipase-A2 receptor (PLA2R) autoantibodies − or as secondary − associated with malignancy, infection, medications, or autoimmune disease. We present a case of biopsy-proven MN with very high serum titer of anti-PLA2R autoantibodies in a patient with a synchronous diagnosis of poorly differentiated esophageal adenocarcinoma and renal cell carcinoma who presented with nephrotic syndrome. Based on the current classification, MN in the presence of active malignancy is diagnosed as secondary and unlikely to have positive anti-PLA2R autoantibodies. This raises several questions: whether this patient has secondary MN associated with malignancy and coincidentally discovered anti-PLA2R autoantibodies, primary MN due to anti-PLA2R autoantibodies with coincidentally discovered malignancy, or whether malignancy can induce the formation of anti-PLA2R autoantibodies that result in MN. This case report highlights the importance of age-appropriate cancer screening, even in patients with presumed primary MN and positive anti-PLA2R autoantibodies.