The majority of renal cell carcinomas (RCCs), represented by conventional clear cell, papillary and chromophobe RCC, and collecting duct carcinoma, are not difficult to diagnose with conventional histology. However, there is a 5% to 10% selective group of RCC that present different morphologic features as well as different clinical behavior. Because of the rarity of these special types of RCC, diagnosis is often difficult. In this issue, we explore in depth the clinicopathologic features of these neoplasms including the XP11 translocation RCC, tubulocystic carcinoma, end stage renal disease associated RCC with oxalate deposition, and the mucinous tubular spindle cell carcinoma. In addition, complementary articles included in this issue review immunohistochemistry in all renal neoplasms and the utilization of virtual karyotyping of single nucleotide polymorphism (SNP) arrays in the diagnosis of granular/oncocytic renal cell neoplasms.
The RCC displaying Xp11 translocation is a rare pediatric neoplasm that is often difficult to diagnose as it has a varied morphology including features that closely resemble those of conventional clear cell RCC. Because RCCs with clear cell morphology in adults are seldom investigated for the Xp11 translocation, the possibility exists that this lesion may be found more often in adult patients. The translocations involve a breakpoint at Xp11.2 that results in gene fusions involving the TFE3 transcription factor gene which maps to this locus.
Mucinous tubular spindle cell carcinoma is a rare form of RCC that presents an indolent behavior although metastatic disease has been well documented in a few reports. As the name implies, it has a characteristic growth pattern consisting of tubules, mucinous stroma and spindle cells that have bland nuclear features, different from atypical spindle cells in sarcomatoid RCCs. Rare cases may develop a dedifferentiated component. Some immunohistochemical similarities to papillary RCC have been described; however, cytogenetic abnormalities are reported to be different.
Tubulocystic carcinoma is a rare renal tumor histologically characterized by closely packed tubules and cysts lined by a single layer of cuboidal cells with eosinophilic cytoplasm, prominent nucleoli, and not uncommonly a hobnail appearance. This tumor has a bland cytologic and histologic appearance and may be misinterpreted as a benign neoplasm; hence the importance of its recognition. This tumor was considered by some authors as a low grade collecting duct carcinoma. However, the clinicopathologic presentation including morphologic features, immunohistochemical and molecular profile, does not support its origin from the collecting ducts of Bellini. This distinct renal epithelial neoplasm has a possible relationship to papillary RCC.
Renal neoplasms frequently develop in the cystic kidneys of end stage renal disease patients treated by long-term dialysis. Although a wide variety of renal neoplasms may be seen in these patients, there is only one tumor characterized by deposition of calcium oxalate crystals in the tumor cells. This type of RCC has distinctive clinicopathologic features and appears to be seen only in kidneys with acquired cystic kidney disease on long-term dialysis. It has a varied growth pattern and characteristically displays abundant extracellular calcium oxalate crystals.
As time goes on, oncologists are rapidly beginning to use targeted therapies directed to specific cell types of renal neoplasms; thus, proper classification of renal cell neoplasms is a must. There is no question that new methodology is being currently used, but such technology is not yet fully available for utilization in current surgical pathology practice. Yet, in the very near future we will have methodology available for the common practice of surgical pathology. We are witnessing the increasing utilization of FISH and CISH analysis as important tools in the final diagnosis of numerous sarcomas. Molecular analysis with SNP microarrays (virtual karyotyping) is now a rapidly developing technique that provides important karyotyping information which is a key for a definitive diagnosis, supplementing the classic morphology of the renal tumors. In this issue, the utilization of this analysis applied to the challenging diagnosis of oncocytic tumors is addressed.
Considering that new markers are being developed often and that it is difficult to keep up with such a vast amount of new knowledge, an overall review of the immunoprofile of renal cell neoplasms is included in this issue. Furthermore, common daily diagnostic problems such as oncocytoma versus chromophobe RCC, papillary RCC versus metanephric adenoma, conventional RCC versus Xp11 translocation RCC, and others are addressed. This discussion also reviews the immune profile of tumors suspected of being metastatic RCC.
In summary, within the category of RCCs, the recent literature has drawn attention to the presence of new rare entities causing potential confusion with known RCC categories. The histopathology of recently described unusual kidney tumors is herein presented, emphasizing new or unusual aspects. Although awareness of these entities will lead into a reasonable diagnostic interpretation, immunohistochemistry and SNP karyotyping will provide the key for the characterization of these rare entities.
© 2010 Lippincott Williams & Wilkins, Inc.