A rare case of co-occurrence of lupus nephritis and lymphoma.

Systemic Lupus Erythematosus (SLE) is an autoimmune disorder known to increase the risk of lymphomas, typically after prolonged immunosuppressive therapy. We report a rare case of a 45-year-old woman who presented with fever, polyarthritis, and anasarca, and was concurrently diagnosed with lupus nephritis and marginal zone lymphoma without prior immunosuppression. Initial evaluation revealed hematologic abnormalities, renal involvement, and axillary lymphadenopathy. Kidney biopsy confirmed class III and V lupus nephritis, while lymph node biopsy unexpectedly revealed low-grade B-cell non-Hodgkin lymphoma. The patient was treated successfully with chemotherapy and supportive lupus therapy, showing marked clinical and laboratory improvement. This case underscores the importance of thorough evaluation of lymphadenopathy in SLE patients, even at initial presentation, and raises awareness of rare concurrent diagnoses. It highlights the complex relationship between autoimmune disease and malignancy, suggesting shared pathogenic mechanisms and the necessity for vigilant, long-term multidisciplinary management.