Elevated serum CA-125 levels in a patient with membranous nephropathy and nephrotic syndrome in absence of malignancy

A woman in her 70s presented with nephrotic syndrome. A renal biopsy confirmed a diagnosis of membranous nephropathy (MN) with negative staining for phospholipase A2 receptor antibody and positive staining for neural epidermal growth factor-like 1. This raised the possibility of secondary MN, which is known to be linked to causes such as malignancy, hepatitis virus infections and autoimmune conditions. During screening for malignancy, a significantly raised CA-125 (cancer antigen 125) was identified. This led to investigations to rule out a gynaecological malignancy, which were negative. The CA-125 level improved with improving serum albumin level and resolution of volume overload. She was treated with immunosuppression for a primary MN with good clinical response. This case highlights the importance of recognising non-malignant causes for raised CA-125 in nephrotic syndrome, allowing management of MN as a primary aetiology with immunosuppression, which is key to recovery and outcomes.