Caratterizzazione immunofenotipica e genotipica di inusuali varianti di carcinomi renali con morfologia a cellule chiare

Background In the past, histomorphological classifications of renal cell carcinomas (RCC) have been based on microscopic features concerning either cell types or growth patterns. The most recent WHO classification of renal tumors (2004) incorporates current knowledge regarding phenotypic profiles and genetic alterations of RCCs, and correlates them with their histological distinctive characters. Thus, clear cell RCC is characterized by frequent CD10 expression and chromosome 3 short arm deletion involving preferentially the VHL tumor suppressor gene at 3p25-26, while papillary RCC shows positive immunostaining for alpha-methylacyl-CoA racemase (AMACR), cytokeratins (CK) 7 and 19, gains (trisomies/tetrasomies) of chromosomes 7 and 17, and loss of Y. Although most cases are easily classifiable among the main subtypes of RCC included in WHO classification, in some RCCs overlapping morphologic findings make subclassification difficult. Therefore, a category of unclassified RCCs has been included in the WHO classification system. In this study, we analyzed pathological features, and cytogenetic and immunohistochemical phenotypes of a series of morphologically hybrid RCCs with extensive clear cell changes and predominantly papillary architecture. Methods Twenty-three RCCs composed of more than 50% clear cells and with more than 50% papillary architecture, one of which arising in end-stage kidney, were selected from the archives of the Departments of Pathology of Universities of Sassari and Verona. As control, 10 cases of conventional clear cell RCCs and 10 cases of papillary RCCs were included in our study. Followup data were available for all cases. Pathological features included tumor size, 2002 primary tumor (T) classification, regional lymph node involvement, distant metastases, Fuhrman’s nuclear grade, coagulative tumor necrosis and sarcomatoid dedifferentiation. Immunohistochemistry was performed with antibodies against CK7, CK19, AMACR and CD10, whereas, for FISH analysis we used centromeric DNA probes (CEP) for chromosome 7 ,17,Y and 3 and a subtelomeric probe for 3p25. Results All papillary RCCs showed positive immunoreactions for CK7, CK19 and AMACR and negative immunostaining for CD10. By FISH analysis, no 3p deletion was found in any of them, whereas chromosome 7 or 17 gains were constantly observed; chromosome Y loss was detected in 4 neoplasms from 5 male patients. In contrast, all conventional clear cell RCC showed positive reactions for CD10 and negative staining for the other antibodies. Moreover, 3p deletions, but no chromosome 7 or 17 gains or chromosome Y losses, were detected in any cases. Immunohistochemistry and FISH analyses distinguished 3 different groups among the hybrid neoplasms. The largest group included 11 RCCs with negative immunostaining for CD10 and strong immunoreactivity for AMACR, CK7 and 19. All of these neoplasms showed gains of chromosome 7 and 17, but no 3p deletions, whereas chromosome Y loss were observed in 6 of 8 tumors from male patients. The pathologic stages were pT1 in 10 cases and pT2 in 1 case; Fuhrman’s nuclear grade ranged between G1 in 10 cases and G2 in 1 case. No necrosis or sarcomatoid dedifferentiation were detected in any cases. Lymph node involvement and distant metastases were always absent. The second group comprises 5 neoplasms strongly immunoreactive for CD10 and unreactive for CK7 and 19 and AMACR. No gains of chromosome 7 and 17 or loss of the chromosome Y were present in any of them, whereas 3p deletion was constantly observed. Coagulative necrosis was found in 3 tumors, two of which showed a pathologic stage pT3 and lymph node involvement or distant metastasis. The third group was composed by 7 RCCs phenotypically and genetically different from either papillary or clear cell carcinoma. No cytogenetic alterations were detected by FISH analyses in 5 of these tumors, whereas immunohistochemistry showed positive reactions for CK7 and 19, with negative staining for CD10 and AMACR in 4 of them, and negative staining for CK7 and 19, with positive reaction for AMACR and CD10 in the remaining case. Two cases among this third group were characterized by complex genetic alterations: the end-stage kidney RCC showed monosomy for chromosome 17 with polisomy for chromosome 7, whereas polisomies for chromosome 7 and 17 with 3p deletion were detected in the remaining tumor; the former was positive for CK7 and 19 antibodies and negative for AMACR and CD10, whereas AMACR was the only positive marker in the latter. Among the third group, the pathologic stage was pT1 in all tumors, and the nuclear grade was G1 in 6 cases and G2 in the remaining case. No necrosis or sarcomatoid dedifferentiation was detected in any cases. Lymph node involvement and distant metastases were always absent. Discussion We studied by immunohistochemical and FISH analyses an unusual group of 23 RCCs with papillary architecture and clear cell changes. The differential diagnosis of these tumors can be difficult, considering that clear cell RCC can show a pseudopapillary architecture, and papillary renal cell carcinoma may exhibit a cellular component with clear cytoplasm. Because the histotype of RCCs has been demonstrated to have a prognostic value, it is important to accurately classify these hybrid neoplasms among the WHO subtypes, or to define specific immunophenotypic and genetic features which might identify a new potential category. By immunohistochemistry and FISH analyses we found that 11 of 23 tumors showed the same phenotypic and genetic profile of papillary RCCs used as control, whereas 5 of them were phenotypically and genetically related with the control group of clear cell RCC. Accordingly, 11 of our cases were classified as papillary RCC, whereas 5 cases were included among clear cell RCCs. Only 7 of 23 hybrid RCCs showing ambiguous phenotypic and/or genetic profiles remained unclassified. All these 7 tumors showed a low nuclear grade and a low pathological stage; moreover, features of biologic aggressiveness, such as coagulative necrosis, sarcomatoid dedifferentiation, lymph node involvement or distant metastasis have not been observed in these neoplasms. Among our series of RCCs, a case arising in end-stage renal disease was also included. This case showed the same cyto-architectural pattern of the remaining RCCs arising in otherwise normal kidneys and was morphologically similar to recently described renal tumors developed in end-stage kidneys and designated as “clear cell papillary renal cell carcinoma of end-stage kidneys”.