Paraneoplastic Membranous Nephropathy in a Patient Diagnosed with Lung Carcinoma in Treatment Immunotherapy: A Case Report and Literature Review

Abstract

Membranous nephropathy is the most frequent cause of nephrotic syndrome in adults, as well as the most common paraneoplastic syndrome associated with solid tumors. In these cases, it is essential to perform an adequate differential diagnosis since there are multiple causes of this syndrome.We describe the case of a 77-year-old male who presented with heart failure in the context of a nephrotic syndrome with hyponatremia and proteinuria, and was finally diagnosed with locally advanced Squamous Cell Lung Carcinoma (SqNSCLC) (stage IIIB). Renal biopsy confirmed the diagnosis of membranous nephropathy, which in the clinical context of the patient and with the negativity of antiRFLPA2 antibodies was compatible with a nephrotic syndrome of paraneoplastic origin.This was a patient with several comorbidities and poor pulmonary function, which limited the therapeutic options, so radical treatment with concomitant chemoradiotherapy and surgery were ruled out. Molecular analysis of the tumor showed a PD-L1 TPS of 20%, so authorization was requested for the use of first-line immunotherapy with Intravenous (IV) Pembrolizumab every 3 weeks off-label.After initiation of immunotherapy treatment, there was evidence of improvement in the analytical parameters and clinical improvement to the point of resolution of the heart failure. In the first CAT scan evaluation, there was evidence of partial response of the disease, which was maintained until completing two years of treatment, with no evidence of progression until the last oncological consultation. Finally, the patient died due to an exacerbation of COPD while maintaining response of his oncologic disease.