Low-grade Collecting Duct Carcinoma Of The Kidney: A Potential Mimic Of Conventional Clear Cell Carcinoma

摘要

Collecting duct carcinoma of the kidney is a well-known, but relatively uncommon tumor characterized by a high cytologic grade, desmoplastic stroma and a poor clinical outcome. Since 1979, however, there have been several reports of low-grade renal carcinoma of putative collecting duct origin. These low-grade tumors were extensively papillary, tubulopapillary or tubulocystic, with a low nuclear grade (usually Furhman grade 1 or 2). Most have conferred a benign follow-up course, even when treated only by partial nephrectomy. The previous reports of such tumors have been variably characterized immunohistochemically and ultrastructurally. We report the cases of a low-grade renal carcinoma of collecting duct origin, arising in the right renal lower pole of a 47-year-old-male with a history of gout and nephrolithiasis. Microscopically, the tumor showed a tubular and tubulocystic pattern and was composed almost exclusively of clear cells, closely mimicking conventional (clear cell) renal cell carcinoma. Tumor cells stained positively for PAS, showed droplet-like staining with Hale's colloidal iron, were variably alcian blue positive and were mucicarmine negative. They were reactive with immunohistochemical antibodies to peanut agglutinin (PNA), Ulex europaeus-1 agglutinin (UEA-1), pan-cytokeratin, CAM 5.2, cytokeratin 7, epithelial membrane antigen (EMA) and vimentin. Electron microscopy showed microvillous-lined tubules, desmosomes, and tonofilaments, with a paucity of mitochondria. The patient was treated by partial nephrectomy and has been without evidence of disease for a follow-up period of 10 months. Introduction Collecting duct carcinomas of the kidney are relatively uncommon neoplasms, generally regarded as high grade tumors expressing phenotypic markers of the normal renal collecting duct, which include high molecular weight cytokeratin (HMWK, 34+E12), Ulex europaeus-1 agglutinin (UEA-1), peanut agglutinin (PNA) and epithelial membrane antigen (EMA) 1,2,3,4. These tumors are grossly situated in the renal medulla with a firm consistency and gray-white color. Microscopically, they are usually tubular or tubulopapillary with a high nuclear grade and markedly desmoplastic stroma. Clinical outcome is poor, with approximately 66% of patients dying of disease within 2 years of diagnosis 4.In 1979, Cromie et al described a low-grade renal carcinoma characterized by a tubular and papillary microscopic pattern, low nuclear grade, absence of desmoplasia and apparent origin from collecting duct epithelium. Follow up clinical course was benign following radical nephrectomy 5. Since that time, additional reports of low-grade renal carcinomas, apparently of collecting duct or distal nephron origin, have been reported, almost all having a benign follow-up clinical course following either radical or partial nephrectomy 6,7,8,9,10. Most of these have been studied histochemically and immunohistochemically, with only 10 examined ultrastructurally 5,7,8. The importance of the presently described case lies in its striking histologic similarity to conventional (clear cell) renal cell carcinoma, with which it might have easily been confused. Case Report A 47-year-old white male was found to have a 2.0-cm solid mass at the lower pole of his right kidney during evaluation for microscopic hematuria. His past medical history was significant for Crohn's disease, type II Diabetes Mellitus and gout. He suffered a single episode of nephrolithiasis four years prior, with intermittent left flank pain and hematuria. Chemical analysis showed the stones to be composed of uric acid. His medications included mesalamine, glyburide and rofecoxib. His physical examination was unremarkable. Laboratory values were significant for serum uric acid level of 7.0 mg/dl. Urinalysis revealed 0-3 white blood cells/hpf, 30-40 red blood cells/hpf , 3-5 epithelial cells/hpf and trace proteins. Renal ultrasound showed a right kidney of 12.4 cm and a left kidney of 12.2 cm with