PLA2R-positive membranous nephropathy treated with rituximab (MENTOR regimen) in a patient with concomitant endometrial carcinoma

A case report.

Abstract

Introduction: Membranous nephropathy (MN) is one of the most common causes of nephrotic syndrome in adults. The M-type phospholipase A2 receptor (PLA2R) is the podocyte antigen responsible for the majority of primary cases, and its detection has revolutionized the diagnosis and monitoring of the disease. Treatment with rituximab, particularly using regimens such as that of the MENTOR study, has demonstrated sustained long-term efficacy. We present a case of PLA2R-positive MN with a good response to rituximab, complicated by the incidental finding of endometrial carcinoma during follow-up.

Case report: A 44-year-old female patient with no significant medical history presented with progressive lower-extremity edema of four months' duration.

Results: The patient exhibited persistent dyslipidemia and nephrotic-range proteinuria (2813 mg/24h), with preserved renal function (creatinine 0.5 mg/dl) and negative autoimmune serology. Renal biopsy confirmed MN with PLA2R positivity—a result corroborated by positive serum anti-PLA2R antibodies (25.2 IU/ml)—with no associated chronic lesions. Treatment was initiated with methylprednisolone pulse therapy followed by oral prednisone, and subsequently rituximab using the MENTOR regimen (two 1 g doses spaced 15 days apart), resulting in a good clinical response: progressive reduction of edema and foamy urine. Following the second dose, she experienced amenorrhea followed by abnormal uterine bleeding; endometrial biopsy revealed grade I endometrial carcinoma (node-negative), which was treated via radical hysterectomy without the need for adjuvant therapy.

Conclusions: This case confirms the efficacy of the MENTOR rituximab regimen in inducing clinical remission in PLA2R-positive MN, consistent with published evidence reporting remission rates exceeding 60% at 24 months. Likewise, it highlights the importance of active gynecological surveillance during immunosuppressive treatment, given the incidental finding of an early-stage endometrial neoplasm with an excellent prognosis following timely management.