Case of renal cell carcinoma with immunotherapy effect mimicking xanthogranulomatous pyelonephritis

Abstract

Abstract Introduction/Objective The histologic features of renal cell carcinoma (RCC) after immunotherapy are not fully established. We report the pathologic findings of one case of clear cell RCC after treatment with pembrolizumab which is a humanized monoclonal anti-PD1 antibody. Methods/Case Report 46-year-old man completed three cycles of pembrolizumab for recurrent basal cell carcinoma. A 5.0 cm mass was incidentally found within left kidney during staging CT scan. He subsequently had left radical nephrectomy. Pathologic examination of nephrectomy specimen identified one 5.0 cm, well-circumscribed, solid mass in the upper pole, confined to the kidney with predominantly hemorrhagic, focally golden-yellow soft cut surface. The remaining parenchyma appears unremarkable. The pelvicalyceal system is not dilated. Sections of tumor show predominance of foamy histiocytes, lymphoplasmacytic infiltrate, and scattered cells having pale or eosinophilic cytoplasm, conspicuous nucleoli and low nuclear: cytoplasm ratio. Cholesterol clefts and hemosiderin deposits are noted. The immunostaining profile highlights areas suspicious for viable tumor cells by using pan-keratin, CK8/18, EMA, CA9 and CD10. Focal positivity in the same area is noted by the stains of PAX 8 and AMACR. However, with numerous histiocytes, it is difficult to determine if the tumor cells are positive for Vimentin. Moreover CD 117 is negative in the tumor cells. Results (if a Case Study enter NA) NA Conclusion Differential diagnosis includes renal cell carcinoma and xanthogranulomatous pyelonephritis. The overall findings support a clear cell RCC affected by the immunotherapy. With immunotherapy-based combinations becoming standard of care in advanced malignancies, it makes the pathological diagnosis more challenging and difficult, especially for incidental tumors.