Diagnostic Complexity in Differentiating Between Primary and Secondary Anti‐PLA2R–Positive Membranous Nephropathy in a Patient With Laryngeal Squamous Cell Carcinoma

Introduction The association between membranous nephropathy (MN) and malignant neoplasms has been extensively studied in recent decades and is well established in the literature. Although PLA2R is the main target antigen in primary MN, there remain uncertainties regarding a possible connection between malignancy and anti‐PLA2R positivity. Case Presentation The aim of this study is to report a rare case of anti‐PLA2R–positive MN in a patient with laryngeal squamous cell carcinoma. A 61‐year‐old male patient, undergoing treatment for laryngeal squamous cell carcinoma for two years, presented with nephrotic syndrome for one month. Renal biopsy was performed, and analyses by light microscopy, immunofluorescence, and electron microscopy concluded that the patient had Stage II MN with mild chronic tubulointerstitial changes. Immunohistochemistry revealed strong, global, and diffuse granular staining in capillary loops for PLA2R and IgG4. Conclusion This case highlights the difficulty in distinguishing between primary and secondary MN in patients with neoplasms such as laryngeal squamous cell carcinoma. The strong PLA2R and IgG4 positivity suggests a primary origin of the disease. However, anti‐PLA2R positivity does not exclude a secondary etiology and warrants careful oncologic evaluation, as it may represent an underrecognized pattern of disease rather than a mere coincidence.