Thrombospondin Type 1 Domain-Containing 7A (THSD7A)-Associated Membranous Nephropathy Leading to Metastatic Neuroendocrine Carcinoma

Idiopathic membranous nephropathy also known as primary membranous nephropathy (PMN) is a common cause of nephrotic syndrome often seen in nondiabetic adults worldwide, rising as high as 40% in adults over the age of 60. Most PMN is mediated by antibodies to the M-type phospholipase A2 receptor (anti-PLA2R) in nearly 70%-80% of individuals. Thrombospondin type 1 domain-containing 7A (THSD7A) accounts for 1%-5% of individuals with PMN. In these individuals, malignancies have a varying incidence of 6%-25%. We present a case of idiopathic membranous nephropathy with anti-PLA2R negative and THSD7A positive with an underlying metastatic neuroendocrine carcinoma. Our goal is to highlight the importance of cancer screening in individuals with THSD7A-positive PMN. In addition, although nonspecific, a negative anion gap may be an indicator of an underlying malignancy.