Ultrastructural Features of Unclassified Renal Cell Carcinoma: Implications for Tumor Re-Classification.
Romualdo V Talento, Karlene Hewan-Lowe, Ming Yin. East Carolina University Brody School of Medicine, Greenville, NC
Background: Unclassified renal cell carcinomas (URCCs) are malignant tumors that are morphologically unlike the recognized variations of the other established categories of renal cell carcinomas (RCCs). In concordance with the WHO 2004 classification, only those RCCs with apparent composites of recognized types, pure sarcomatoid morphology without recognizable epithelial elements, mucin production, rare mixtures of epithelial as well as stromal elements, and unrecognizable cell types that do not readily fit into one of the other known categories are assigned a diagnosis of URCC. URCC is an aggressive form of RCC because most cases are at an advanced stage at presentation, with higher rates of metastases and lower survival rates. Currently, there are no detailed reports on the ultrastructural features of URCCs or that address the impact of the ultrastructural features on the categorization of URCCs.
Design: The purpose of this study was to compare the ultrastructural findings of URCCs with those of the primary established categories of RCC (clear cell, papillary, chromophobe) and to determine whether there were ultrastructural features that would justify reclassification of a carcinoma assigned the diagnosis of URCC. Electron microscopy (EM) was performed on eight cases of high-grade renal tumors with solid growth patterns, without features of known RCC subtypes, urothelial carcinomas, or other recently described entities, such as mucinous tubular and spindle cell carcinoma or tubulocystic carcinoma of the kidney. The patients ranged in age from 49 years to 75 years (median 67 years). The range in maximum tumor dimension was from 3.3 cm to 20.0 cm (median 8.4 cm).
Results: Tumor cells of the examined URCCs show loss of cellular polarity with no apparent basal lamina. Rare, elongated desmosomal junctions and occasional tangled brush border-like microvilli are seen between the tumor cells. The cytoplasm shows abundant rough endoplasmic reticulum (RER) with no increased lipid or glycogen. Rare, rounded mitochondria and microvesicles are present. There are varying numbers of lysosomes of different sizes. Markedly irregular nuclei with prominent nucleoli are seen in the majority of cells.
Conclusions: The examined URCCs did not show ultrastructural morphology resembling the primary established categories of RCC or a specific line of tubular differentiation. The irregular nuclei and abundant RER were the major ultrastructural features observed, suggesting that URCCs are poorly differentiated renal carcinomas.
Wednesday, March 2, 2011 9:30 AM
Poster Session V # 279, Wednesday Morning