Update Advances in Renal Neoplasia Recommendations From the 2012 International Society of Urological Pathology Consensus Conference Brett Delahunt, John R. Srigley, Rodolfo Montironi, and Lars Egevad The International Society of Urological Pathology (ISUP) 2012 Consensus Conference made recommendations regarding the classification, prognostic factors, staging, and immunohistochemical and molecular assessment of adult renal tumors. There was consensus that 5 entities should be recognized as novel tumors: tubulocystic renal cell carcinoma (RCC), acquired cystic diseaseeassociated RCC, clear cell papillary RCC, microphthalmia transcription factorefamily translocation RCC [in particular t(6; 11) RCC], and hereditary leiomyomatosis RCC syndromee associated RCC. In addition, 3 rare epithelial carcinomas were considered emerging or provisional entities: thyroidlike follicular RCC, succinate dehydrogenase B deficiencyeassociated RCC, and anaplastic lymphoma kinase translocation RCC. There were also a number of suggested modifications to existing World Health Organization 2004 categories, with the new classification to be known as the ISUP Vancouver Classification. Tumor morphotype, sarcomatoid/rhabdoid differentiation, and tumor necrosis were identified as significant prognostic parameters for RCC. The ISUP Grading System was accepted with grades 1-3 of clear cell and papillary RCC being based on nucleolar prominence, whereas extreme nuclear pleomorphism or sarcomatoid and/or rhabdoid differentiation defined grade 4 tumors. It was agreed that chromophobe RCC should not be graded. Consensus guidelines were formulated for specimen handling, and it was agreed that renal sinus invasion is present when tumor is in direct contact with fat or loose connective tissue of the sinus or if there is involvement of endothelial-lined spaces within the renal sinus, regardless of the size. The role of biomarkers in the diagnosis and assessment of prognosis of renal tumors was considered, and panels of immunohistochemical markers were identified for use in specific differential diagnostic scenarios. UROLOGY 83: 969e974, 2014.
2014 Elsevier Inc.

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he International Society of Urological Pathology (ISUP) acts as the international reference organization for urologic pathology. Since its establishment in 1992, the Society has convened consensus conferences that have provided international guidelines for the classification of bladder tumors, Gleason grading of prostatic carcinoma, and the handling and staging of radical prostatectomy specimens.1 In 2012, the Society sought consensus on a variety of issues relating to recent advances in the field of renal neoplasia, and this resulted in the formulation of a contemporary classification of renal tumors, the recognition of valid prognostic factors for renal cell carcinoma (RCC)—including the establishment of guidelines for grading these tumors—recommendations for specimen handling and staging, and the development of panels of immunohistochemical stains to facilitate identification of tumor morphotypes.2-5 Financial Disclosure: The authors declare that they have no relevant financial interests. From the Department of Pathology and Molecular Medicine, Wellington School of Medicine, University of Otago, Wellington, New Zealand; the Department of Pathology and Molecular Medicine, McMaster University, Hamilton, Ontario, Canada; the Institute of Pathological Anatomy and Histology, Polytechnic University of Medicine, United Hospitals, Ancona, Italy; and the Department of Oncology-Pathology, Karolinska University Hospital, Solna, Stockholm, Sweden Reprint requests: Brett Delahunt, M.D., F.R.C.P.A., F.R.C.Path., Department of Pathology and Molecular Medicine, Wellington School of Medicine and Health Sciences, University of Otago, P.O. Box 7343, Wellington 6242, New Zealand. E-mail: [email protected] Submitted: October 18, 2013, accepted (with revisions): February 3, 2014

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CONSENSUS CONFERENCE ORGANIZATION As is customary for consensus conferences coordinated by the ISUP, the organization of the conference was overseen by a steering committee, with each member having considerable experience in the consensus process. Four key topics, (1) classification of renal tumors, (2) prognostic factors, (3) specimen handling and tumor staging, and (4) immunohistochemical and molecular markers, were identified by the steering group, and workgroups were assigned to each of these.6 Informed by the evaluation of relevant published data, including the recently published renal tumor survey results from the European Network of Uropathology,7 each workgroup was tasked with the compilation of a survey to canvas current opinion and identify specific areas of controversy. The completed survey consisted of 87 multiple choice questions, with options to provide additional comment as free text. The survey was circulated to all members of the ISUP in October 2011, with a cutoff date for return of replies by November 20, 2011. Replies were received from 206 members (North America 55%, Europe 26%, Australia and New Zealand 7%, Asia 7%, South America 4%, and the Middle East 1%). Working group participants and those members of the Society who had returned the survey by the cutoff date 0090-4295/14/$36.00 http://dx.doi.org/10.1016/j.urology.2014.02.004

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Table 1. New and emerging RCCs and novel concepts identified at the 2012 ISUP Consensus Conference New tumor entities Acquired cystic diseaseeassociated RCC Clear cell (tubulo) papillary RCC Hereditary leiomyomatosis RCC syndromeeassociated RCC MiT family translocation RCC [including t(6:11) RCC] Tubulocystic RCC Emerging tumor entities ALK translocation RCC Succinate dehydrogenase B deficiencyeassociated RCC Thyroid-like follicular RCC Novel concepts Multilocular cystic renal cell neoplasm of low malignant potential Hybrid oncocytic/chromophobe tumors Epithelioid angiomyolipoma: low/intermediate/high risk Cystic nephroma/mixed epithelial and stromal tumor of kidney ALK, anaplastic lymphoma kinase; ISUP, International Society of Urological Pathology; MiT, microphthalmia transcription factor; RCC, renal cell carcinoma.

were invited to participate in the formal consensus conference. This was convened in Vancouver, Canada, on March 17, 2012, in conjunction with the Annual Scientific Meeting of the United States and Canadian Academy of Pathology. The conference was attended by 133 voting delegates from 29 countries (North America 57%, Europe 23%, Australia and New Zealand 8%, Asia 6%, South America 4.5%, and the Middle East 1.5%). The conference was divided into 4 sections, with the members of each workgroup presenting a comprehensive review of the literature and the results of the survey. A series of questions was then put to the meeting with a formal ballot being taken electronically. A majority of 65% of the voting delegates was taken as a consensus in accordance with the established practice of the ISUP.8 A total of 63 questions were considered at the meeting, and of these, a consensus was achieved in 42 (67%).

THE VANCOUVER CLASSIFICATION OF RENAL NEOPLASIA During the consensus conference, 8 forms of renal neoplasia were proposed for recognition, and of these, 5 were considered to be sufficiently well characterized to be included in the revised classification (Table 1). The remaining 3 tumors were designated as new and emerging entities. In addition to this, recommendations were made concerning refinements to tumor categories included within the 2004 World Health Organization (WHO) Renal Tumor Classification. New Renal Tumor Entities A variety of morphotypes of RCC occur in patients with end-stage kidney disease and, in particular, those with acquired cystic disease. Acquired cystic diseaseeassociated RCC is a novel morphotype characteristically seen in these 970

kidneys, with the incidence increasing in patients having long-term dialysis.9 These tumors occur as nodules in the walls of acquired cysts and have a variety of histologic patterns, with tumor cells showing prominent vacuolation, resulting in a cribriform architecture (Fig. 1A). Oxalic acid crystals are almost always present. These tumors show a variety of genetic changes, with gains in chromosomes 1, 2, 3, 6, 7, 16, and Y being reported. At each stage, these tumors appear to behave more aggressively than other RCC subtypes. Originally described as clear cell papillary RCC, clear cell (tubulo) papillary RCC occurs both sporadically and in association with acquired renal cystic disease.10,11 These tumors are well circumscribed and are often encapsulated. On microscopy, they have a variable morphology with a tubular, cystic, and/or papillary architecture (Fig. 1B). Tumor cells have a clear cytoplasm and exhibit positive immunoexpression of cytokeratin 7 and have a characteristic pattern of carbonic anhydrase IX staining. Genetically, mutations of the VHL gene or gains of chromosomes 7 and 17, typical of clear cell and papillary RCCs, respectively, are not seen. Although follow-up of these tumors is limited, no cases of metastatic disease have been reported. Although hereditary leiomyomatosis RCC syndromee associated RCC is included in the 2004 WHO classification, it was considered as a variant of type 2 papillary RCC.12 It is now recognized that these tumors have a characteristic morphology and are now considered a unique morphotype of RCC.13 These tumors are part of the hereditary leiomyomatosis RCC syndrome. This is autosomal dominant and is associated with germline mutations in the fumarate hydratase gene, sited at chromosome 1q42. The syndrome is characterized by the presence of cutaneous and uterine leiomyomas and onethird of patients develop RCC. The renal tumors have a papillary, alveolar, solid, or tubular architecture with the characteristic features being a large nucleus and a prominent nucleolus, with a clear peripheral halo (Fig. 1C). These tumors behave aggressively and have a poor prognosis compared with other hereditary forms of RCC or clear cell and papillary morphotypes. Xp11 translocation RCC is included as a specific morphotype of RCC in the 2004 WHO renal tumor classification. These tumors have a breakpoint that involves the TFE3 transcription factor gene at Xp11.2. Tumors with fusion to one of a number of genes (ASPL, PRCC, NonO, PSF, and CLTC) have been reported. A small group of translocation RCCs varies from this genetic profile. These show Alpha-TFEB gene fusion, resulting from t(6; 11)(p21; q12) and are designated t(6,11) translocation RCC.14 At the meeting, there was consensus that along with Xp11 translocation RCC, t(6,11) translocation RCC should be considered under the designation microphthalmia transcription factor family translocation RCC. These tumors most commonly occur in young adults and have a variety of morphologic patterns. Most typically, these tumors are biphasic, UROLOGY 83 (5), 2014

Figure 1. Newly recognized renal tumor entities: (A) acquired cystic diseaseeassociated renal cell carcinoma (RCC), (B) clear cell (tubulo) papillary RCC, (C) hereditary leiomyomatosis RCC syndromeeassociated RCC, (D) t(6,11) translocation RCC, and (E) tubulocystic RCC. (Color version available online.)

consisting of large and small epithelioid cells (Fig. 1D). The small epithelioid cells form nests of rosettes clustered around the basement membrane material. These tumors express melanocytic antigens and are rarely positive for epithelial markers. The behavior of these tumors is yet to be fully characterized, although 10% of the 30 reported cases have developed fatal metastatic disease. Tubulocystic RCC had been previously described under various terms and had been considered a low-grade variant of collecting duct carcinoma. Macroscopically, tubulocystic RCC is well circumscribed, having the appearance of complex multilocular fluid-filled cysts.15-18 Histologically, these tumors consist of tubules and cysts showing varying degrees of dilatation (Fig. 1E). The tumor cells have eosinophilic cytoplasm and typically have a large irregular nucleus and prominent nucleolus. Although these tumors were originally thought to be of collecting duct origin, limited studies indicate gene expression similar to papillary RCC, with gains of chromosomes 7 and 17 and loss of Y being commonplace. Although 4 cases of metastatic disease have been reported, most tumors are pT1-2 at diagnosis and appear to have an excellent prognosis. Emerging and Provisional Tumor Morphotypes Following the identification of a variant of RCC resembling well-differentiated follicular carcinoma of the thyroid gland, 14 further cases have been reported in the literature. Designated thyroid-like follicular RCC, these tumors are tan brown, homogeneous, and well circumscribed. Microscopically, they consist of tumor follicles of varying size containing dense eosinophilic colloid-like material.19 The genetics and immunohistochemical expression of these UROLOGY 83 (5), 2014

tumors are, as yet, not fully characterized, although thyroid follicular cell markers, thyroglobulin, and thyroid transcription factor (TTF-1) are negative. Most of the cases reported to date have shown an indolent behavior, although metastases to lymph nodes in 2 cases and 1 case with pulmonary metastases have been reported. A fusion of the anaplastic lymphoma kinase (ALK) gene with the gene for the cytoskeletal protein vinculin (VCL) resulting from the translocation t(2:10)(p23; q22) has been reported in 2 tumors. VCL-ALK translocation RCC appears to have a characteristic appearance consisting of cells with a polygonal to spindled morphology.20 While these 2 cases were associated with sickle cell trait, 2 further RCCs showing ALK fusion with different partner genes have been described, although neither of these showed a sickle cell association. More recently, an additional 2 cases of RCC demonstrating ALK fusion have been reported; however, in these cases, the fusion partner is unknown. The third tumor designated as an emerging RCC entity is succinate dehydrogenase B mutation-associated RCC.21 These tumors are seen in patients with germline succinate dehydrogenase B mutation, which is associated with a syndrome consisting of pheochromocytoma, paraganglioma, and type 2 gastrointestinal stromal tumors. Microscopically, these tumors are characterized by the presence of compact nests of eosinophilic polygonal cells. Cytoplasmic vacuoles and pale eosinophilic cytoplasmic inclusions are commonly seen, and these represent giant mitochondria. Less than 10 cases have been reported to date, and follow-up is limited. Of note, sarcomatoid change was identified in 2 patients with metastatic disease, 1 of whom died of tumor-related causes. 971

New Concepts Relating to Recognized Tumor Types Multilocular clear cell RCC is recognized as a subtype of clear cell RCC and like clear cell RCC shows loss of heterozygosity at chromosome 3p. These tumors are characterized by the presence of multiple cysts lined by clear cells, which exhibit low-grade pleomorphism. Multiple follow-up studies have shown these tumors to have an excellent prognosis with no reports of either metastatic disease or tumor-related deaths. In view of this favorable outcome, there was just consensus (65%) that these tumors be redesignated as multilocular cystic renal cell neoplasms of low malignant potential. It is recognized that rare tumors consist of a mixture of cells having the morphologic features of oncocytoma and chromophobe RCC. Known as hybrid oncocytic/chromophobe tumors, these occur sporadically, as part of renal oncocytosis and in association with the Birt-Hogg-Dube syndrome. Three variants are recognized: (1) a mixture of typical oncocytoma and chromophobe RCC cells, (2) scattered chromophobe cells displaying perinuclear halos and occasional binucleation in an otherwise classical oncocytoma, and (3) large vacuolated eosinophilic cells showing a mild-to-moderate degree of nuclear pleomorphism arranged in a nested oncocytoma-like pattern.22 These tumors show various genetic profiles that differ from both oncocytoma and chromophobe RCC. Hybrid oncocytic/chromophobe tumor appears to behave in a benign fashion. Epithelial angiomyolipoma is recognized as having malignant potential, although it appears that not all these tumors behave in this manner. There was consensus that these tumors should be divided on the basis of the presence or absence of morphologic atypia. There was also near consensus (64%) that tumors be divided into low-, intermediate-, and high-risk groups, rather than simply classifying as benign/malignant, based on the number of recognized malignant criteria present (metastases, necrosis, size >7 cm, extra-renal extension, renal vein infiltration, and carcinoma-like growth pattern).23 Mixed epithelial and stromal tumor of the kidney and cystic nephroma are benign tumors having both stromal and epithelial components. Although these tumors are classified separately in the 2004 WHO renal tumor classification, they share similarities in clinical presentation and morphology. In addition, both tumors show positive expression of estrogen and progesterone receptors and have a similar gene expression profile. In view of this, there was consensus that these 2 tumors should be considered variants of the same neoplasm.

PROGNOSTIC MARKERS Of the numerous potential morphologic prognostic parameters for RCC, only 5 were considered by the consensus conference to be sufficiently clinically validated to be reported in routine practice. The ISUP Grading System Several grading classifications for RCC have been proposed, being based on architectural, cytoplasmic, and/or 972

nuclear features, and of these, the Fuhrman classification is in widespread use. The Fuhrman classification is a 3-tiered system in which nuclear size and shape, as well as nucleolar prominence, are assessed simultaneously to assign a grade. Much debate has surrounded the utility of the classification, and questions have been raised regarding its validity as a prognostic parameter.24 In particular, it has been noted that the classification has poor reproducibility, no recommendations are provided regarding the stratification of grading parameters if these give conflicting results, and there are conflicting results in studies that correlate Fuhrman grading with overall and disease-free survival. Recent studies have shown that for clear cell and papillary RCC, assessment of nucleolar size alone for grading 1-3 tumors is a more powerful prognostic discriminator. At the consensus conference, a grading system based on nucleolar prominence was proposed, and the ISUP Grading System for RCC was recommended as a substitute for Fuhrman grading. The ISUP System has 4 tiers (grade 1—nucleoli inconspicuous or absent at 400 magnification [objective magnification 40], grade 2—nucleoli prominent at 400 magnification [objective magnification 40], grade 3— nucleoli prominent at 100 magnification [objective magnification 10], and grade 4—extreme nuclear pleomorphism, tumor giant cells, and/or sarcomatoid/ rhabdoid change). There was consensus that this grading system was applicable to clear cell and papillary RCC. In the absence of evidence that grading chromophobe RCC was of prognostic value, there was consensus that these tumors should not be graded. Other Prognostic Factors There was consensus that for RCCs, tumor morphotype was of prognostic significance. In particular, it was noted that for all stages, both papillary and chromophobe RCCs had a more favorable outcome than clear cell RCC. There was consensus that collecting duct RCC was associated with a poor prognosis and that clear cell (tubulo) papillary RCC had an excellent prognosis, with no instances of metastatic disease being noted in the limited number of cases reported to date. There was also consensus that type 1 papillary RCC was associated with a more favorable outcome than papillary RCC with type 2 morphology. Sarcomatoid and rhabdoid differentiation is recognized as being associated with high rates of tumor recurrence and metastasis. There was consensus that for these 2 extreme forms of tumor dedifferentiation, the morphotype of the original tumor should be reported. There was also agreement that for sarcomatoid RCC, a minimum percentage of tumor area was not necessary for diagnostic purposes, although it was agreed that the percentage area of sarcomatoid component within an RCC should be reported. Recent studies have shown tumor necrosis within RCC to be of prognostic significance, and this was supported by the conference. It was specified that both macroscopic UROLOGY 83 (5), 2014

and microscopic necroses should be reported and that a percentage of the total area showing necrosis, within an individual tumor, should be specified.

SPECIMEN HANDLING The conference provided consensus guidelines for handling of surgical specimens. There was agreement that tumor sampling should follow the model of 1 block/cm of tumor. In cases of multiple tumors, it was agreed that the 5 largest tumors should be sampled. For the assessment of extra-renal extension of tumor, there was consensus that perinephric fat invasion should be reported when tumor was seen touching the fat or extending as irregular tongues into the perinephric tissue. There was also consensus that tumor in direct contact with renal sinus fat or the loose connective tissue of the sinus or infiltration of endotheliallined spaces within the renal sinus should be considered as renal sinus invasion (American Joint Committee on Cancer tumor, nodes, and metastases [TNM] staging category pT3a). There was consensus that renal vein margin positivity required adherent tumor present at the tumor margin microscopically. Although it was noted that lymph nodes are found in only