Membranous Nephropathy as a Paraneoplastic Syndrome in Cancer of Unknown Primary.

BACKGROUND/AIM:Membranous nephropathy (MN) is a nephrotic syndrome with both idiopathic and secondary etiologies. The mechanism of cancer-associated MN is presumed to involve the immunological production of antibodies against a tumor antigen, although little is known about the detailed mechanism. Lung cancer is a major neoplasm associated with cancer-associated MN. However, the simultaneous occurrence of secondary MN in patients with cancer of unknown primary (CUP) remains unclear. CASE REPORT:Here, we present a case of secondary MN in a 72-year-old female as a paraneoplastic syndrome in CUP. Thoracic radiotherapy up to a total of 60 Gy was initially performed on the right subclavian and mediastinal lymph nodes. Computed tomography revealed marked shrinking of these lymph nodes, and the secondary MN also improved without any symptoms. CONCLUSION:The presence of proteinuria in patients with CUP suggests the possibility of secondary MN as a rare differential diagnosis.