A 52-year-old Japanese female was admitted to our hospital for microhematuria, proteinuria and progressive renal dysfunction. Two years prior to admission, she was diagnosed with lung adenocarcinoma and multiple bone and brain metastases, and was treated with gefitinib (250 mg/day). Treatment for 6 months induced partial response with 30% regression of the primary lung tumor, and resolution of metastatic tumors. After confirmation of the partial remission state, we performed percutaneous renal biopsy. Glomeruli showed mild to moderate mesangial proliferation, segmental endocapillary proliferation and occasional fibrocellular crescent formation. In addition, severe interstitial fibrosis and tubular atrophy relative to the degree of glomerular sclerosis were noted. Immunofluorescence microscopy showed predominant IgA deposition in the mesangial area. Electron microscopy revealed subepithelial and paramesangial electron-dense deposits. In consideration of the prognosis of lung cancer and complication of immunosuppressive treatment, we continued gefitinib only and closely followed-up the clinical course in the outpatient clinic. Sixteen months later, she continued to have proteinuria and microhematuria, and the severity of renal dysfunction was still the same. However, the lung cancer started to increase in size. This is quite an unusual case presenting histologically with tubulointerstitial nephritis and IgA nephropathy in a patient on long-term treatment with gefitinib.
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