Papillary renal cell carcinoma and collecting duct carcinoma combination. A case report and review of synchronous renal cell carcinoma subtypes in the same kidney

Collecting duct carcinoma (CDC), also known as Bellini duct carcino-ma, is a rare neoplasm comprising less than 1% of renal epithelial tumors [1]. Collecting duct carcinoma is an aggressive neoplasm and is thought to arise from the collecting ducts of renal medulla [2]. Papillary renal cell carcinoma (PRCC) comprises 10% of renal cell carcinomas (RCC) and has distinct cytogenetic and molecular features [3]. Concurrent primary neoplasms of the kidney have been rarely reported in the literature as an association of RCC and transitional cell carcino-ma (TCC) or oncocytoma [4–6]. But coexistence of the RCC subtypes in the same kidney is exceptional. To the best of our knowledge, 20 cases have been reported to date as synchronous RCC subtypes in the same kidney [7–21]. Among them there have been only two cases of synchronous CDC and PRCC. In these cases, the tumors were usually seen as separate masses. In contrast, in some reports tumor components were seen as a single mass or " tumor in tumor " or with obvious histological transition [10, 12, 13, 15, 16]. Here we present the third case of CDC and PRCC association and the first one of this association as a " tumor-in-tumor " morphology. A 42-year-old man initially presented with flank pain and hematuria. His personal or family histories were not contributory. In ultrasonography, soft tissue density was detected at the lower pole of the right kidney. An abdominal computed tomographic scan demonstrated a 38 mm cystic lesion and 35 mm mass with equal density in the renal cortex. A right radical nephrectomy with lymph node dissection was performed. Macroscopic examination showed a 10 cm, solid, gray-white mass containing a 3.5 cm cystic area with papillary features in the renal parenchyma extending to the pelvis. Microscopically, the solid part of the mass revealed infiltrative tubuloglandular formations in a desmoplastic stroma. Tumor cells had large hyperchromatic and pleomorphic nuclei and relatively scant cyto-plasm. The cystic part of the tumor showed entirely different histology consisting of papillary structures lined with columnar cells having coarse vesicular nuclei, prominent nucleoli and large eosinophilic cytoplasm. Dys-plastic features were seen in the epithelium of the distal collecting ducts too. The tumor invaded the renal capsule and extended into the perire-nal fat. Gerota's fascia, renal vein, ureter, and adrenal gland were free of