Biphasic alveolosquamoid renal carcinoma: a histomorphological, immunohistochemical, molecular genetic, and ultrastructural study of a distinctive morphologic variant of renal cell carcinoma

Clear Cell Renal Cell Carcinoma With Syncytial-Type Multinucleated Giant Tumor Cells: A Clinicopathologic Study of 14 Cases

The presence of syncytial-type multinucleated giant tumor cells with emperipolesis in clear cell renal cell carcinoma (RCC) is uncommon, with only 31 cumulative published cases to date. After a rereview of 125 clear cell RCC of World Health Organization/International Society of Urological Pathology grade 3 or 4, 14 clear cell RCCs with admixed syncytial-type giant cells (to our knowledge, the largest series to date) were found with a mean patient age of 67 years and with no sex difference (M = 7, F = 7). Mean tumor size was 7.3 cm. The syncytial-type giant cells comprised between 2% and 20% of the tumor and were present mainly around areas of necrosis. Five tumors were staged as pT1 or pT2, 8 as pT3, and 1 as pT4. Other findings included sarcomatoid differentiation (3/14), rhabdoid differentiation (4/14), and emperipolesis (12/14). Positive immunostains included keratin AE1/AE3 (13/13), carbonic anhydrase 9 and CD10 (12/14 each), vimentin (8/14), EMA (5/12), and alpha-methyacyl-CoA racemase (3/12). Keratin 7, keratin 20, human melanoma black 45, KIT, TFE3, cathepsin K, CD68, CD61, and beta human chorionic gonadotropin were negative. Six of 13 patients had recurrence or metastases during a mean follow-up time of 56 months. Four of 13 patients died of disease, 2 of 13 patients were alive with the disease, and 7 of 13 patients had no evidence of disease. Although the incidence of finding syncytial-type multinucleated giant tumor cells in clear cell RCC is low (approximately 1.2%), given that a subset of the patients showed poor outcomes while lacking other poor histologic parameters (eg, sarcomatoid or rhabdoid differentiation), it may be prudent to recognize and report this feature when encountered.

Papillary Renal Cell Carcinoma: Evolving Classification by Combined Morphologic and Molecular Means

Papillary renal cell carcinoma classification has evolved as a result of attentive morphologic observations by pathologists coupled with specific immunohistochemical, molecular, and clinical data. Refinement of this relatively common diagnostic category of renal neoplasia has resulted in the parsing out of specific renal cell carcinoma subtypes that no longer belong in the papillary renal cell carcinoma category and can have distinct familial and prognostic implications (eg, fumarate hydratase (FH)-deficient renal cell carcinomas). In addition, evolving classification has enabled more accurate diagnosis by surgical pathologists (through the description of recognizable morphologic variants). In many cases, molecular findings have aided and confirmed morphologic categorization. The combination of morphologic and molecular findings continues to provide important prognostic information for patients and their clinicians.

Biphasic papillary (biphasic squamoid alveolar) renal cell carcinoma: a clinicopathologic and molecular study of 17 renal cell carcinomas including 10 papillary adenomas

Biphasic papillary renal cell carcinoma (synonymous with biphasic squamoid alveolar renal cell carcinoma) is considered within the spectrum of papillary renal cell carcinoma (PRCC). With < 70 reported cases of biphasic PRCC, there is limited data on the pathologic spectrum and clinical course. Seventeen biphasic PRCC cases and 10 papillary adenomas with similar biphasic morphology were assessed. The mean age of the biphasic PRCC patients was 62 years (male to female ratio of 1.8:1), from 10 partial nephrectomies, 6 radical nephrectomies, and 1 biopsy. The mean tumor size was 3.6 cm (range 1.6-8 cm), with 24% showing multifocality. Fifteen out of 17 cases were limited to the kidney (one of which was staged as pT2a but had lung metastases at diagnosis) and 2/17 cases were staged as T3a. All tumors showed typical biphasic morphology with an extent of squamoid foci widely variable from 10 to 95%. Emperipolesis was identified in 88% of cases. All biphasic PRCC tested exhibited positivity for PAX8 (16/16), keratin 7 (17/17), EMA (15/15), AMACR (17/17), and vimentin (12/12) in both large and small cells; cyclin D1 was only expressed in the large cells (16/16). The 10 papillary adenomas showed a similar immunoprofile to biphasic PRCC. NGS testing performed on 13 biphasic PRCC revealed 4 (31%) harboring MET SNVs. In 1/5 (20%) papillary adenomas, a pathogenic MET SNV was identified. Biphasic PRCC is rare with a generally similar immunoprofile to "type 1" PRCC but with notable strong positivity for cyclin D1 in the large cell component. Although most of the biphasic PRCC cases were of small size, low stage, and with an indolent behavior, one patient had metastatic disease and one patient died of the disease.

Prognostic value of IKBIP in papillary renal cell carcinoma

BACKGROUND

I kappa B kinase interacting protein, a highly conserved gene, has rarely been reported in cancer. According to previous study, IKBIP has only been shown to promote malignant progression of glioma. In other malignant tumors, few reports have examined the function of IKBIP, especially in papillary renal cell carcinoma. Therefore, the molecular profiles and clinical prognostic values of the IKBIP in papillary renal cell carcinoma remain undetermined.

METHODS

Several bioinformatic platforms and Immunohistochemistry were used to clarify the expression and prognostic values of IKBIP in Papillary renal cell carcinoma.

RESULTS

In this study, GEPIA and TIMER platform were used to identify mRNA expression of IKBIP in papillary renal cell carcinoma. And our results revealed that IKBIP mRNA expression was up-regulated in papillary renal cell carcinoma than in its corresponding normal tissues. In addition, high mRNA expression levels of IKBIP were correlated with age, pathological stage, pathological T stage and pathological N stage. Moreover, High IKBIP mRNA expression was negatively correlated with overall survival (OS) and disease-free survival (DFS) in patients of papillary renal cell carcinoma. Besides, Multivariate analysis indicated that IKBIP mRNA expression was an independent prognostic factor for patients of papillary renal cell carcinoma. Furthermore, Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis showed IKBIP co-expressed genes were enriched in homologous recombination, DNA replication, cell cycle, Mismatch repair, Fanconi anemia pathway, P53 signaling pathway and nucleotide excision repair. And Immunohistochemical profile showed that protein expression of IKBIP was higher in papillary renal cell carcinoma than adjacent normal tissue.

CONCLUSIONS

Overall, our findings reveled that IKBIP may act as a novel and potential tumor factor to accelerate papillary renal cell carcinoma progression, meanwhile, IKBIP could serve as a promising target for treating papillary renal cell carcinoma.

Recurrent CYP2A6 gene mutation in biphasic hyalinizing psammomatous renal cell carcinoma: Additional support of three cases

Biphasic hyalinizing psammomatous renal cell carcinoma (BHP RCC) with NF2 gene mutations is a newly described provisional category of renal cell carcinoma (RCC). Here we described three additional cases of BHP RCC with CYP2A6 gene mutation besides NF2 gene. The carcinomas were predominantly unencapsulated, and two of them had a rounded, nodular interface with the native kidney while one had perirenal adipose tissue invasion. Histopathologically, all neoplasms had a characteristic biphasic appearance of smaller cells clustering around basement membrane material within larger acini, forming pseudorosettes or a glomeruloid pattern. The smaller cells were focally spindle-shaped in two carcinomas. Psammoma bodies were shown in two carcinomas. Cellular necrosis and perineural invasion was identified in one case. Immunohistochemically, Vimentin, EMA, P504s were extensively expressed while RCC and CD10 were only expressed in larger cells. CK7 was positive in one tumor. CYP2A6 gene mutation (CYP2A6 NM_000762.6: exon4:c.A580G:p.K194E) was revealed in three tumors by Whole-genome exome sequencing, which was further confirmed by Sanger sequencing. Only one case harbored a somatic termination mutation in NF2 gene. NF2 promoter methylation was observed in the other two cases. Clinically, one patient died of disease with widespread bone metastases confirmed by biopsy at the ninth month after surgery but the other two patients had no evidence of recurrence or metastases (follow-up period 9-90 months). Our findings validated previously described clinicopathological features and NF2 gene mutation or promoter methylation of BHP RCC. In addition, we reported different IHC pattern of BHP RCC and further revealed the recurrent CYP2A6 genetic alteration.

WHO 2022 landscape of papillary and chromophobe renal cell carcinoma

The 5th edition of the WHO Classification of Tumours of the Urinary and Male Genital Systems contains relevant revisions and introduces a group of molecularly defined renal tumour subtypes. Herein we present the World Health Organization (WHO) 2022 perspectives on papillary and chromophobe renal cell carcinoma with emphasis on their evolving classification, differential diagnosis, and emerging entities. The WHO 2022 classification eliminated the type 1/2 papillary renal cell carcinoma (pRCC) subcategorization, given the recognition of frequent mixed tumour phenotypes and the existence of entities with a different molecular background within the type 2 pRCC category. Additionally, emerging entities such as biphasic squamoid alveolar RCC, biphasic hyalinising psammomatous RCC, papillary renal neoplasm with reverse polarity, and Warthin-like pRCC are included as part of the pRCC spectrum, while additional morphological and molecular data are being gathered. In addition to oncocytomas and chromophobe renal cell carcinoma (chRCC), a category of 'other oncocytic tumours' with oncocytoma/chRCC-like features has been introduced, including emerging entities, most with TSC/mTOR pathway alterations (eosinophilic vacuolated tumour and so-called 'low-grade' oncocytic tumour), deserving additional research. Eosinophilic solid and cystic RCC was accepted as a new and independent tumour entity. Finally, a highly reproducible and clinically relevant universal grading system for chRCC is still missing and is another niche of ongoing investigation. This review discusses these developments and highlights emerging morphological and molecular data relevant for the classification of renal cell carcinoma.

Papillary renal cell carcinoma: current and controversial issues

PURPOSE OF THE REVIEW

Papillary renal cell carcinoma (pRCC) is the second most frequent renal cancer subtype and represents 15-20% of all RCC. Classification of pRCC is changing because novel tumour entities have been discovered in the last years. In this review, we summarise recent studies relevant for the understanding of the molecular complexity and the broader differential diagnosis of pRCC.

RECENT FINDINGS

It has been 25 years ago, that pRCC was morphologically subdivided into type 1 and type 2. Recently described tumour entities in the 2022 WHO classification challenged this concept and allow a new view on the molecular background in pRCC. Biphasic hyalinizing psammomatous RCC and papillary renal neoplasm with reversed polarity are emerging tumour entities derived from the new concept of molecularly defined RCC subtypes. Immune checkpoint inhibition and tyrosine kinase inhibitors have been introduced as the new backbone in the first-line treatment of advanced pRCCs. To identify novel targeted treatments for patients with pRCC it is crucial to investigate the specific molecular background of pRCC considering emerging pRCC subtypes.

SUMMARY

In the future, a deeper understanding of the correlation between molecular aberrations and new pRCC subtypes may improve the classification of pRCC patients and could reveal potential predictive biomarkers for each subgroup.

Distal Tubular Hyperplasia: A Proposal for a Unique Form of Renal Tubular Proliferation Distinct From Papillary Adenoma

We identified an unusual pattern of renal tubular proliferation associated with chronic renal disease, found in 23 patients, diffusely (n=12), or focally (n=11). Incidence was 5% of end-stage renal disease kidneys from one institution (8/177) and 7/23 patients with acquired cystic kidney disease-associated renal cell carcinoma from another. Most (19 patients) had 1 or more neoplasms including papillary (n=9), acquired cystic kidney disease (n=8), clear cell (n=4), or clear cell papillary (n=3) renal cell carcinoma. All (20 men, 3 women) had end-stage renal disease. The predominant pattern (n=18) was the indentation of chronic inflammation into renal tubules forming small polypoid structures; however, 5 had predominantly hyperplastic epithelium with less conspicuous inflammation. In 14 patients both patterns were appreciable, whereas the remainder had only the inflammatory pattern. Immunohistochemistry was positive for cytokeratin 7, high-molecular-weight cytokeratin, PAX8, and GATA3. Staining for alpha-methylacyl-CoA racemase was negative or weak, dramatically less intense than papillary neoplasms or proximal tubules. CD3 and CD20 showed a mixture of B and T lymphocytes in the inflammatory areas. Fluorescence in situ hybridization showed no trisomy 7 or 17 or loss of Y (n=9). We describe a previously uncharacterized form of renal tubular proliferation that differs from papillary adenoma (with weak or negative alpha-methylacyl-CoA racemase, lack of trisomy 7 or 17, and sometimes diffuse distribution). On the basis of consistent staining for high-molecular-weight cytokeratin and GATA3, we propose the name distal tubular hyperplasia for this process. Future studies will be helpful to assess preneoplastic potential and etiology.

Towards a new WHO classification of renal cell tumor: what the clinician needs to know-a narrative review

In 1952, renal cell carcinomas had been divided into 2 categories—clear cell or granular cell—depending upon their cytoplasmic staining characteristics. In the following years, the inventory of renal epithelial tumors has expanded by the addition of tumors named by their architectural pattern (i.e., papillary RCC, tubulocystic RCC), anatomic location (i.e., collecting duct carcinoma, renal medullary carcinoma), associated diseases (i.e., acquired cystic disease-associated RCCs). With the extensive application of molecular diagnostic techniques, it becomes possible to detect genetic distinctions between various types of renal neoplasm and discover new entities, otherwise misdiagnosed or diagnosed as unclassified RCC. Some tumors such as ALK rearrangement-associated RCC, MiT family translocation renal carcinomas, SDH-deficient renal cancer or FH-deficient RCC, are defined by their molecular characteristics. The most recent World Health Organization (WHO) classification of renal neoplasms account for more than 50 entities and provisional entities. New entities might be included in the upcoming WHO classification. The aim of this review is to summarise and discuss the newly acquired data and evidence on the clinical, pathological, molecular features and on the prognosis of new RCC entities, which will hopefully increase the awareness and the acceptance of these entities among clinicians and improve prognostication for individual patients.

MET alterations in biphasic squamoid alveolar papillary renal cell carcinomas and clinicopathological features

Biphasic squamoid alveolar papillary renal cell carcinoma (BSA-PRCC) is a recently studied lesion considered a morphologic variant of papillary renal cell carcinoma (RCC), more closely related to type 1. Considering the role of proto-oncogene MET in both sporadic type 1 papillary RCC and hereditary papillary RCC, we aimed to explore the role of MET activation in the oncogenesis of BSA-PRCC. We identified 17 patients with either unique (n = 14) or multiple (n = 3) BSA-PRCC, all localized, and performed an integrative analysis of MET status in 18 formalin-fixed paraffin-embedded tumors combining next-generation sequencing analysis, fluorescent in situ hybridization and immunohistochemistry. Trisomy 7 was found in 86% of tumors (14/16) without MET amplification at 7q31 (15/15). A pathogenic MET genetic variant was identified in 60% (9/15) of cases, at the germline level in 57% (4/7) of tested patients or at the somatic level (5/11). MET expression was observed in all tumors with a higher value of combined score in large cells (mean 97%, range 80-100%) than in small cells (mean 74%, range 10-100%) and was lower in two cases without MET copy number gain. In conclusion, our study provides additional evidence to consider biphasic squamoid alveolar papillary RCC as a morphological variant of type 1 papillary renal RCC. Our data strongly suggest that MET represents a major oncogenic driver gene in BSA-PRCC, harboring a higher frequency of MET mutation that encourages to further explore the benefice of anti-MET targeted therapies for aggressive BSA-PRCC.

Biphasic Squamoid Alveolar Renal Cell Carcinoma of the Kidney Involved by Atypical CD5-Positive B-Cells

Biphasic squamoid alveolar renal cell carcinoma (BSARCC) is a recently described kidney cancer entity with <60 published cases so far. Some unique features of BSARCC include distinct squamoid and alveolar morphology forming glomeruloid configurations and 2 types of tumor cells with different immunoprofiles. Although the mechanism is unknown, neutrophils and cellular materials engulfed by larger tumor cells (described as "emperipolesis") are observed in all reported cases including the current one. In this article, we report a case of a 70-year-old man who presented with an incidental renal mass during workup for immunoglobulin M monoclonal gammopathy of unknown significance and cold agglutinin autoimmune hemolytic anemia. A detailed pathologic evaluation and immunohistochemical studies revealed BSARCC colliding with atypical CD5+ monoclonal B-cells.

Cytomorphology, immunoprofile, and management of renal oncocytic neoplasms

BACKGROUND

The goal of this study was to evaluate the morphology, immunoprofile, and management of renal oncocytoma (RO), hybrid oncocytic tumor (HOT), and chromophobe renal cell carcinoma (ChRCC).

METHODS

Forty-seven cases of RO, 7 cases of HOT, and 25 cases of ChRCC were included in the study. Tissue microarrays were prepared for immunohistochemical evaluation.

RESULTS

Large sheets of cells with transverse vessels, and higher nuclear grade were seen more often in ChRCC than in RO or HOT. Tumor cells of RO were more uniform in size and shape relative to HOT and ChRCC. The cytoplasmic features of RO were more uniformly granular relative to HOT and ChRCC, which exhibited variable cytoplasmic features. CK7 and MUC1 were expressed more frequently and diffusely in ChRCC (54% and 94%, respectively) than RO (4% and 52%, respectively) and HOT (0% and 71%, respectively). AMACR and PAX8 were more frequently expressed diffusely in RO (67% and 42%, respectively) than in HOT (0% and 0%, respectively) or ChRCC (14% and 11%, respectively). Most HOT (57%) and CHRCC (60%) patients underwent nephrectomy. Cryoablation was the treatment of choice for 24% of patients with ChRCC, 2% of patients with RO, and 0% of patients with HOT. The majority of patients with RO (88%) opted for active surveillance-a much higher rate than that for patients with HOT (29%) or ChRCC (12%).

CONCLUSION

Some cytologic features and immunomarkers are useful in differentiating RO, HOT, and ChRCC. Because no immunomarker or morphologic finding is specific by itself, a combination of morphologic features with immunohistochemistry appears to be the most reliable way to distinguish ChRCC, HOT, and RO on biopsy samples. Subclassification of renal oncocytic tumors into specific categories impacts clinical management and downstream treatment selection.

Assessing Genomic Copy Number Alterations as Best Practice for Renal Cell Neoplasia: An Evidence-Based Review from the Cancer Genomics Consortium Workgroup

Renal cell neoplasia are heterogeneous with diverse histology, genetic alterations, and clinical behavior that are diagnosed mostly on morphologic features. The Renal Cell Neoplasia Workgroup of the Cancer Genomics Consortium systematically evaluated peer-reviewed literature on genomic studies of renal cell carcinoma (RCC), including clear cell RCC, papillary RCC, chromophobe RCC, and the translocation RCC involving TFE3, TFEB and MITF rearrangements, as well as benign oncocytoma, which together comprise about 95% of all renal cell neoplasia. The Workgroup curated recurrent copy number alterations (CNAs), copy-neutral loss-of-heterozygosity (cnLOH), rearrangements, and mutations, found in each subtype and assigned clinical relevance according to established criteria. In clear cell RCC, loss of 3p has a disease-initiating role and most likely also in progression with mutations detected in VHL and other genes mapped to this arm, and loss of 9p and/or 14q has well-substantiated prognostic utility. Gain of chromosomes 7 and 17 are hallmark CNAs of papillary RCC, but patterns of other CNAs as detected by chromosomal microarray analysis (CMA) afford sub-classification into Type 1 and 2 with prognostic value, and for further sub-stratification of Type 2. Inherent chromosome loss in chromophobe RCC as detected by CMA is useful for distinguishing the eosinophilic variant from benign oncocytoma which in contrast exhibits few CNAs or rearranged CCND1, but share mitochondrial DNA mutations. In morphologically atypical RCCs, rearrangement of TFE3 and TFEB should be considered in the differential diagnosis, portending an aggressive RCC subtype. Overall, this evidence-based review provides a validated role for assessment of CNAs in renal cell neoplasia in the clinical setting to assist in renal cell neoplasm diagnosis and sub-classification within subtypes that is integral to the management of patients, from small incidentally found renal masses to larger surgically resected specimens, and simultaneously identify the presence of key alterations portending outcome in malignant RCC subtypes.

[The morphological characteristics and immunophenotype of renal cell carcinomas with eosinophilic cytoplasm]

Eosinophilic cellular renal cell carcinomas embrace a wide range of histological types described in the 2016 WHO International Classification of Kidney Tumors. A variety of histological manifestations associated with the features of tumor morphogenesis in this group poses difficulties in differential diagnosis.

AIM

to investigate the morphological and immunophenotypic features of rare types of renal cell carcinomas with eosinophilic cytoplasm.

SUBJECTS AND METHODS

An investigation was conducted using a surgical material from 294 patients with a kidney tumor. An immunohistochemical (IHC) study was performed on paraffin sections according to the standard protocol using a wide panel of antibodies.

RESULTS

Based on a morphological analysis and IHC study, the tumors were divided into 3 groups: 1) 127 (43%) oncocytic tumors that expressed classical IHC markers for oncocytoma and chromophobe renal cell carcinoma; 2) 50 (17%) oncocytic tumors that did not correspond to the immunophenotypes of oncocytoma and chromophobe renal cell carcinoma; and 3) 117 (40%) eosinophilic cellular nononcocytic renal tumors.

CONCLUSION

With the advent of the current differential diagnostic criteria, the classification of renal cell carcinomas continues to expand. To date, a hybrid oncocytic/chromophobic tumor, eosinophilic solid and cystic renal cell carcinoma, and follicular kidney cancer should be regarded as new nosological entities.

A first case report of primary epithelial myoepithelial carcinoma-like renal tumor showing a perivascular pseudorosette-like pattern: Description of morphologic, immunohistochemical, and genetic features

RATIONALE

Over the past decade, although several new entities of renal tumors have emerged, a form of renal cell carcinoma (RCC) that morphologically resembles epithelial-myoepithelial carcinoma has not been reported thus far. Herein, we describe a case of an unusual renal tumor that remained unclassified under a current RCC subtype, and briefly present its morphologic, immunophenotypic, and genetic features.

PATIENT CONCERNS

The patient was an 85-year-old man who presented with hematuria and flank pain. Imaging studies revealed a left renal mass without enlarged lymph nodes. There were no abnormal masses or nodules in other organs.

DIAGNOSES

The patient underwent no other treatment except the left radical nephrectomy under a clinical diagnosis of invasive urothelial carcinoma and was discharged on the thirteenth day. Histologically, the renal tumor showed biphasic proliferation of epithelial (strongly cytokeratin-positive; P63, P40, and vimentin-negative) and myoepithelial (strongly vimentin-positive; focal P63 and P40-positive; and weakly cytokeratin-positive) cells arranged in a perivascular pseudorosette-like pattern. No mutations were detected in multiple gene tests. According to the pathological structure, the patient was diagnosed as primary epithelial myoepithelial carcinoma-like renal tumor.

INTERVENTIONS

To the best of our knowledge, the present tumor has not been previously described, and thus, this variant has not been integrated into a known form of PCC. Therefore, we cannot diagnose this type of tumor with other types of kidney tumors.

OUTCOMES

Three years after primary diagnosis, the patient died of multiple organ failure result from multiple distant metastases.

LESSONS

We present the first case of carcinoma of the kidney with EMC-like features and a perivascular pseudorosette-like growth pattern. Clinicians should be aware of the features of this uncommon variant of RCC to avoid diagnostic delays or misdiagnosis and prevent unnecessary or inappropriate treatment.

Biphasic squamoid alveolar renal carcinoma with positive CD57 expression: A clinicopathologic study of three cases

Biphasic squamoid alveolar renal cell carcinoma (BSARCC) is a rare and recently characterized form of papillary renal cell carcinoma (PRCC). Herein, we describe three cases of BSARCC that were CD57+. Among a total of 90 cases of PRCC, three cases were found to be consistent with a diagnosis of BSARCC. In addition to reviewing these cases, we reviewed the relevant literature pertaining to this form of cancer and assessed the immunohistochemical staining for CD57 on the available tumor samples. The three BSARCC cases in the present study were composed of two primary populations of cells. Tumors stained positive for CK, PAX8, CK7, CK19, AMACR, EMA, and vimentin. Larger cells expressed detectable levels of cyclin D1, and expression of CD57 was limited to the larger cells. All three patients were alive and free of disease during the most recent follow-up. Our results suggest that the CD57 positivity of at least a subset of cases should necessitate their differentiation from cases of metanephric adenoma.

Emerging entities of renal cell neoplasia

The current classification of renal cell carcinoma (RCC) was formulated at the meeting of the World Health Organization Renal Tumor Panel in 2015, with the results published in the fourth edition of the World Health Organization Classification of Tumours of the Urinary System and Male Genital Organs Bluebook in 2016. At that meeting a number of tumor types were designated as emerging or provisional entities as it was felt that they were insufficiently characterized to merit inclusion as a recognized type of RCC. One tumor type included in this designation was thyroid-like follicular RCC. Since the publication of the 2016 classification this tumor type has been further characterized and in addition to this, detailed studies on three other types of RCC (multifocal oncocytoma-like tumors associated with oncocytosis, eosinophilic solid and cystic RCC and biphasic squamoid alveolar RCC) have been published. It is now apparent that these four tumors are unique morphotypes and genotypes of RCC, and are likely to be included in the next edition of the World Health Organization classification of renal tumors. Multifocal oncocytoma-like tumors associated with oncocytosis is a benign process characterized by the presence of hundreds to thousands of oncocytic tumors in a single kidney. These tumors occur sporadically and are unrelated to the tumors of Birt-Hogg-Dubé syndrome. Eosinophilic solid and cystic RCC is characterized by a solid and cystic architecture with tumor cells consisting of bulky eosinophilic and granular cytoplasm with intracytoplasmic vacuolation. Thyroid-like follicular RCC occurs in younger patients with a female predominance. The tumor bears a striking resemblance to follicular carcinoma of the thyroid with follicles containing intraluminal proteineacous material resembling thyroglobulin. Immunostains for thyroid markers are negative. Finally, biphasic squamoid alveolar RCC consists of aggregates of large cells with pale eosinophilic cytoplasm usually arranged in a glomeruloid/alveolar pattern and surrounded by a border of basophilic cells with scanty cytoplasm. The genotype of the tumor, as well its recorded association with typical papillary RCC, has led to the suggestion that it is related to type 1 papillary RCC.

High proliferation rate and TNM stage but not histomorphological subtype are independent prognostic markers for overall survival in papillary renal cell carcinoma

Papillary renal cell carcinoma (PRCC) is currently divided in 2 subtypes. We reviewed a large cohort of PRCC and correlated subtype, morphological features and diagnostic marker expression with overall survival (OS) to uncover differences between the 2 subtypes. Three hundred seventy-six renal tumors initially diagnosed as PRCC with clinical and survival data were collected from the participating centers. Two hundred forty-six tumors were classified as PRCC1 (65.4%) and 130 as PRCC2 (34.6%) and graded according to the 2016 World Health Organization/International Society of Urological Pathology grading system. Morphological features (abundant cytoplasm, necrosis, fibrous stroma, foamy macrophages and psammoma bodies) were noted. Immunohistochemical stains (MIB1, p53, Racemase, EMA, CK7, CK20, E-Cadherin) were performed using tissue microarrays. χ²-Tests, log-rank tests and uni- and multivariate Cox regression analysis were performed. Both subtypes displayed different morphological features and immunohistochemical profiles: abundant cytoplasm was more frequent in PRCC2, while foamy macrophages were more common in PRCC1. Abundant cytoplasm and presence of psammoma bodies were associated with poorer OS. PRCC1 showed more frequent CK7 expression, PRCC2 more frequent E-Cadherin, p53 and higher MIB1 expression (>15%). Expression of Racemase and CK7 was associated with better OS, while high MIB1 (>15%) was associated with poorer OS. In multivariate analysis, the only independent predictors of OS were proliferation (MIB1), tumor stage, metastasis and age at surgery. Subtype was not an independent prognostic factor. Therefore, PRCC subtype on its own is not suitable for estimating survival. More data focusing on PRCC tumor biology is needed to define prognostic subgroups, especially in PRCC2.

Biphasic papillary renal cell carcinoma is a rare morphological variant with frequent multifocality: a study of 28 cases

AIMS

To further characterise biphasic squamoid renal cell carcinoma (RCC), a recently proposed variant of papillary RCC.

METHODS AND RESULTS

We identified 28 tumours from multiple institutions. They typically showed two cell populations-larger cells with eosinophilic cytoplasm and higher-grade nuclei, surrounded by smaller, amphophilic cells with scanty cytoplasm. The dual morphology was variable (median 72.5% of tumour, range 5-100%); emperipolesis was found in all cases. The male/female ratio was 2:1, and the median age was 55 years (range 39-86 years). The median tumour size was 20 mm (range 9-65 mm). Pathological stage pT1a was found in 21 cases, pT1b in three, and pT3a and pT3b in one each (two not available). Multifocality was found in 32%: multifocal biphasic RCC in one case, biphasic + papillary RCC in two cases, biphasic + clear cell RCC in three cases, biphasic + low-grade urothelial carcinoma of the renal pelvis in one case, and biphasic + Birt-Hogg-Dubé syndrome in one case. Positive immunostains included: PAX8, cytokeratin (CK) 7, α-methylacyl-CoA racemase, epithelial membrane antigen, and vimentin. Cyclin D1 was expressed only in the larger cells. The Ki67 index was higher in the larger cells (median 5% versus ≤1%). Negative stains included: carbonic anhydrase 9, CD117, GATA-3, WT1, CK5/6, and CK20; CD10 and 34βE12 were variably expressed. Gains of chromosomes 7 and 17 were found in two evaluated cases. Follow-up was available for 23 patients (median 24 months, range 1-244 months): 19 were alive without disease, one was alive with recurrence, and one had died of disease (two had died of other causes).

CONCLUSIONS

Biphasic papillary RCC is a rare variant of papillary RCC, and is often multifocal.

Chromosomal numerical aberration pattern in papillary renal cell carcinoma: Review article

Traditionally, papillary renal cell carcinomas (PRCCs) have been divided in two subgroups - type 1 and type 2. Based on recent molecular and genetic developments in the understanding of RCCs, it seems that this traditional classification may not be adequate and that the spectrum of PRCCs is much wider than initially proposed. Small series of distinct types of PRCC which do not fit into the above mentioned categories have been described in the literature. Published studies investigating molecular genetic changes in various types of PRCCs have shown that the molecular genetic features are remarkably heterogeneous across the whole spectrum of PRCCs. Of all PRCC subtypes/variants, PRCC type 1 seems to be a genetically uniform group, while other types showed different degrees of heterogeneity. Among different molecular-genetic features, chromosomal numerical aberration status is one of the most frequently studied features so far. It is becoming more evident that tumor type-specific chromosomal numerical aberration status in PRCCs may not exist. In this review, we present the most current knowledge concerning chromosomal numerical aberration status in PRCCs.

Biphasic Squamoid Alveolar Renal Cell Carcinoma: A Distinctive Subtype of Papillary Renal Cell Carcinoma?

Biphasic squamoid alveolar renal cell carcinoma (BSARCC) has been recently described as a distinct neoplasm. Twenty-one cases from 12 institutions were analyzed using routine histology, immunohistochemistry, array comparative genomic hybridization (aCGH) and fluorescence in situ hybridization. Tumors were removed from 11 male and 10 female patients, whose age ranged from 53 to 79 years. The size of tumors ranged from 1.5 to 16 cm. Follow-up information was available for 14 patients (range, 1 to 96 mo), and metastatic spread was found in 5 cases. All tumors comprised 2 cell populations arranged in organoid structures: small, low-grade neoplastic cells with scant cytoplasm usually lining the inside of alveolar structures, and larger squamoid cells with more prominent cytoplasm and larger vesicular nuclei arranged in compact nests. In 9/21 tumors there was a visible transition from such solid and alveolar areas into papillary components. Areas composed of large squamoid cells comprised 10% to 80% of total tumor volume. Emperipolesis was present in all (21/21) tumors. Immunohistochemically, all cases were positive for cytokeratin 7, EMA, vimentin, and cyclin D1. aCGH (confirmed by fluorescence in situ hybridization) in 5 analyzable cases revealed multiple numerical chromosomal changes including gains of chromosomes 7 and 17 in all cases. These changes were further disclosed in 6 additional cases, which were unsuitable for aCGH. We conclude that tumors show a morphologic spectrum ranging from RCC with papillary architecture and large squamoid cells to fully developed BSARCC. Emperipolesis in squamoid cells was a constant finding. All BSARCCs expressed CK7, EMA, vimentin, and cyclin D1. Antibody to cyclin D1 showed a unique and previously not recognized pattern of immunohistochemical staining. Multiple chromosomal aberrations were identified in all analyzable cases including gains of chromosomes 7 and 17, indicating that they are akin to papillary RCC. Some BSARCCs were clinically aggressive, but their prognosis could not be predicted from currently available data. Present microscopic, immunohistochemical, and molecular genetic data strongly support the view that BSARCC is a distinctive and peculiar morphologic variant of papillary RCC.

Renal cell carcinoma in kidney allografts: histologic types, including biphasic papillary carcinoma

Kidney transplant recipients are at increased risk for malignancy, with about 5% incidence of cancer in native end-stage kidneys. Carcinoma in the renal allograft is far less common. Prior studies have demonstrated a propensity for renal cell carcinomas (RCCs) of papillary subtypes in end-stage kidneys, and perhaps in allograft kidneys, but most allograft studies lack detailed pathologic review and predate the current classification system. We reviewed our experience with renal carcinoma in kidney allografts at 2 academic centers applying the International Society of Urological Pathology classification, informed by immunohistochemistry. The incidence of renal allograft carcinoma was about 0.26% in our population. Of 12 allograft carcinomas, 6 were papillary (50%), 4 were clear cell (33%), 1 was clear cell (tubulo)papillary, and 1 chromophobe. Two of the papillary carcinomas had distinctive biphasic glomeruloid architecture matching the newly named "biphasic squamoid alveolar" pattern and were difficult to classify on core biopsies. The 2 cell types had different immunophenotypes in our hands (eosinophilic cells: RCC-/CK34betaE12+ weight keratin +/cyclin D1+; clear cells: RCC+/cytokeratin high molecular weight negative to weak/cyclin D1-). None of the patients experienced cancer recurrences or metastasis. Our study confirms the predilection for papillary RCCs in kidney allografts and highlights the occurrence of rare morphologic variants. Larger studies are needed with careful pathologic review, which has been lacking in the literature.

Case Report: Multifocal biphasic squamoid alveolar renal cell carcinoma

A multifocal biphasic squamoid alveolar renal cell carcinoma in a 68-year-old man is reported. Four different peripheral tumor nodules were identified on gross examination. A fifth central tumor corresponded to a conventional clear cell renal cell carcinoma. Biphasic squamoid alveolar renal cell carcinoma is a rare tumor that has been very recently characterized as a distinct histotype within the spectrum of papillary renal cell carcinoma. Immunostaining with cyclin D1 seems to be specific of this tumor subtype. This is the first reported case with multifocal presentation.

Case Report: Multifocal biphasic squamoid alveolar renal cell carcinoma

A multifocal biphasic squamoid alveolar renal cell carcinoma in a 68-year-old man is reported. Four different peripheral tumor nodules were identified on gross examination. A fifth central tumor corresponded to a conventional clear cell renal cell carcinoma. Biphasic squamoid alveolar renal cell carcinoma is a rare tumor that has been very recently characterized as a distinct histotype within the spectrum of papillary renal cell carcinoma. Immunostaining with cyclin D1 seems to be specific of this tumor subtype. This is the first reported case with multifocal presentation.

The evolving classification of renal cell neoplasia

The classification of renal cell neoplasia is morphologically based; however, this has evolved over the last 35 years with the incorporation of genetic characteristics into the diagnostic features of some tumors. The 2013 Vancouver classification recognized 17 morphotypes of renal parenchymal malignancy and two benign tumors. This classification included the newly established entities tubulocystic renal cell carcinoma (RCC)), acquired cystic disease-associated RCC, clear cell (tubulo) papillary RCC, microphthalmia transcription factor family translocation RCC and hereditary leiomyomatosis RCC syndrome-associated RCC. In addition to these newly described forms of RCC there are a number of novel tumors that are currently recognized as emerging entities. These are likely to be incorporated into subsequent classifications and include thyroid-like follicular RCC, succinate dehydrogenase B mutation-associated RCC, ALK translocation RCC, tuberous sclerosis complex-associated RCC, and RCC with (angio) leiomyomatous stroma.