Solid papillary renal cell carcinoma: clinicopathologic, morphologic, and immunohistochemical analysis of 10 cases and review of the literature

What Is New in Pathologic Diagnosis and Classification of the Common Renal Cell Neoplasms?

Diagnostic challenges remain among the common renal cell carcinoma (RCC) subtypes. High-grade clear cell RCC may have deceptive patterns, for example BAP1-deficient tumors. Subtyping type 1 and 2 papillary RCC is no longer recommended, as former type 2 tumors may now be contain other diagnostic entities, such as FH-deficient RCC, MITF family RCC, or others. Clear cell papillary tumor is no longer considered carcinoma due to its highly favorable behavior. However, imperfect examples are best considered clear cell RCC. Oncocytic renal neoplasm of low malignant potential has been proposed as a borderline category in the absence of overt malignant features.

Contemporary review of papillary renal cell carcinoma-current state and future directions

Historically, papillary renal cell carcinoma (PRCC) was divided into two types, type 1 and type 2, based solely on morphology. However, it is apparent that PRCC is far more complex and represents a histological, clinical, and molecular spectrum. There has been a significant evolution in our understanding of PRCC, highlighted by the recognition of new and molecularly defined entities that were previously included in PRCC type 2. This contemporary review addresses the evolving concepts regarding the PRCC, including why it is no longer needed to subtype PRCC, the current molecular landscape, prognostic parameters, and PRCC variants, including biphasic PRCC, papillary renal neoplasm with reverse polarity, and Warthin-like PRCC. Pathologists should also be aware of the potential mimickers of both low-grade and high-grade PRCCs as well as some new and emerging entities that may show papillary growth that should be excluded in the diagnostic workup. The evolving knowledge of PRCC biomarkers, morphologic patterns, and PRCC variants could also have important implications for clinical management. Lastly, the heterogeneity within the PRCC spectrum needs to be further studied, aiming to better stratify PRCC for appropriate clinical management and systemic therapy.

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.

Papillary Renal Cell Carcinoma With Microcystic Architecture Is Strongly Associated With Extrarenal Invasion and Metastatic Disease

Papillary renal cell carcinoma (PRCC) is well-recognized as a morphologically and molecularly heterogenous group of kidney tumors with variable clinical behavior. Our goal was to analyze a unique histologic pattern of PRCC we have observed in routine practice to evaluate for potential clinical significance or distinct molecular signature. We identified 42 cases of PRCC showing a morphologically distinct architecture characterized by numerous epithelial-lined cysts containing the papillary tumor (herein called "microcysts"), which are typically separated by fibrous stroma. Of the initial 42 case test set with microcystic features, 23 (55%) were stage pT3a or higher. Most tumors had strong and diffuse cytoplasmic immunoreactivity for CK7 (93%, 37/40) and AMACR (100%, 40/40). Fumarate hydratase staining was retained in all cases tested (39/39). We performed next-generation sequencing on 15 of these cases with available tissue and identified chromosomal alterations commonly reported in historically "type 1" PRCC, notably multiple chromosomal gains, particularly of chromosomes 7 and 17, and MET alterations. However, alterations in pathways associated with more aggressive behavior (including SETD2, CDKN2A, and members of the NRF pathway) were also identified in 6 of 15 cases tested (40%). Given this molecular and immunophenotypic data, we subsequently reviewed an additional group of 60 consecutive pT2b-pT3 PRCCs to allow for comparisons between cases with and without microcysts, to assess for potential associations with other recently described histologic patterns (ie, "unfavorable architecture": micropapillary, solid, and hobnail), and to assess interobserver reproducibility for diagnosing architectural patterns and grade. Of the total combined 102 PRCCs, 67 (66%) had microcystic architecture within the intrarenal component but were commonly admixed with other patterns (39% had micropapillary, 31% solid, and 31% hobnail). Twenty-seven cases (26%) had metastatic disease, and 24 of these 27 (89%) had microcystic architecture in the intrarenal tumor. Within the pT3 subset, 21 of 22 cases with metastases (95%) had extrarenal invasion as either individual microcysts in renal sinus fat or aggregates of microcysts bulging beyond the confines of the capsule. Backward elimination and stepwise regression methods to detect features significantly associated with adverse outcome identified solid architecture (hazard ratio [HR]: 6.3; confidence interval [CI]: 2.1-18.8; P=0.001), hobnail architecture (HR: 5.3; CI: 1.7-16.7; P=0.004), and microcystic architecture at the tumor-stromal interface (HR: 4.2; CI: 1.1-16.7; P=0.036) as strongest. Of architectural patterns and grade, the microcystic pattern had a substantial interobserver agreement (κ score=0.795) that was highest among the 6 observers. In summary, PRCCs with microcystic architecture represents a subset of historically "type 1" PRCC with a predilection for morphologically distinctive extrarenal involvement and metastatic disease. Microcysts co-vary with other "unfavorable" architectural patterns also associated with higher risk for aggressive disease (ie, micropapillary, hobnail, and solid), but microcysts were more common and have superior interobserver reproducibility. These findings suggest that microcystic PRCC should be recognized as a potentially aggressive histologic pattern of growth in PRCC.

New developments in existing WHO entities and evolving molecular concepts: The Genitourinary Pathology Society (GUPS) update on renal neoplasia

The Genitourinary Pathology Society (GUPS) reviewed recent advances in renal neoplasia, particularly post-2016 World Health Organization (WHO) classification, to provide an update on existing entities, including diagnostic criteria, molecular correlates, and updated nomenclature. Key prognostic features for clear cell renal cell carcinoma (RCC) remain WHO/ISUP grade, AJCC/pTNM stage, coagulative necrosis, and rhabdoid and sarcomatoid differentiation. Accrual of subclonal genetic alterations in clear cell RCC including SETD2, PBRM1, BAP1, loss of chromosome 14q and 9p are associated with variable prognosis, patterns of metastasis, and vulnerability to therapies. Recent National Comprehensive Cancer Network (NCCN) guidelines increasingly adopt immunotherapeutic agents in advanced RCC, including RCC with rhabdoid and sarcomatoid changes. Papillary RCC subtyping is no longer recommended, as WHO/ISUP grade and tumor architecture better predict outcome. New papillary RCC variants/patterns include biphasic, solid, Warthin-like, and papillary renal neoplasm with reverse polarity. For tumors with 'borderline' features between oncocytoma and chromophobe RCC, a term "oncocytic renal neoplasm of low malignant potential, not further classified" is proposed. Clear cell papillary RCC may warrant reclassification as a tumor of low malignant potential. Tubulocystic RCC should only be diagnosed when morphologically pure. MiTF family translocation RCCs exhibit varied morphologic patterns and fusion partners. TFEB-amplified RCC occurs in older patients and is associated with more aggressive behavior. Acquired cystic disease (ACD) RCC-like cysts are likely precursors of ACD-RCC. The diagnosis of renal medullary carcinoma requires a negative SMARCB1 (INI-1) expression and sickle cell trait/disease. Mucinous tubular and spindle cell carcinoma (MTSCC) can be distinguished from papillary RCC with overlapping morphology by losses of chromosomes 1, 4, 6, 8, 9, 13, 14, 15, and 22. MTSCC with adverse histologic features shows frequent CDKN2A/2B (9p) deletions. BRAF mutations unify the metanephric family of tumors. The term "fumarate hydratase deficient RCC" ("FH-deficient RCC") is preferred over "hereditary leiomyomatosis and RCC syndrome-associated RCC". A low threshold for FH, 2SC, and SDHB immunohistochemistry is recommended in difficult to classify RCCs, particularly those with eosinophilic morphology, occurring in younger patients. Current evidence does not support existence of a unique tumor subtype occurring after chemotherapy/radiation in early childhood.

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.

[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.

Molecular Genetics of Renal Cell Tumors: A Practical Diagnostic Approach

Renal epithelial cell tumors are composed of a heterogeneous group of tumors with variable morphologic, immunohistochemical, and molecular features. A "histo-molecular" approach is now an integral part of defining renal tumors, aiming to be clinically and therapeutically pertinent. Most renal epithelial tumors including the new and emerging entities have distinct molecular and genetic features which can be detected using various methods. Most renal epithelial tumors can be diagnosed easily based on pure histologic findings with or without immunohistochemical examination. Furthermore, molecular-genetic testing can be utilized to assist in arriving at an accurate diagnosis. In this review, we presented the most current knowledge concerning molecular-genetic aspects of renal epithelial neoplasms, which potentially can be used in daily diagnostic practice.

Papillary renal cell carcinoma with prominent spindle cell stroma - tumor mimicking mixed epithelial and stromal tumor of the kidney: Clinicopathologic, morphologic, immunohistochemical and molecular genetic analysis of 6 cases

Papillary renal cell carcinoma (PRCC) is currently a well-studied type of RCC. In addition to PRCC type 1, there are a number of other subtypes and variants of PRCCs which have been reported. We describe a series of 6 PRCCs with papillary, micropapillary and/or tubulopapillary architecture and prominent spindle cell stroma, resembling stroma in mixed epithelial and stromal tumor of the kidney (MESTK) or sarcomatoid RCC. Clinicopathologic, morphologic, immunohistochemical and molecular features were analyzed. All patients were males with an age range of 44-98 years (mean 65.3, median 65.5 years). Tumor size ranged from 2.4-11.4 cm (mean 5.8, median 4.5 cm). Follow-up data were available for 4 patients, ranging from 3 to 96 months (mean 42.75, median 36 months). Epithelial cells were mostly cylindrical with eosinophilic cytoplasm, showing nuclear grade 2 and 3 (ISUP/WHO). In all cases, loose to compact prominent stroma composed of spindle cells, without malignant mesenchymal heterologous elements was detected. No atypical mitoses were found, while typical mitoses were rare in both epithelial and stromal components. Epithelial cells were positive for CK7, AMACR, and vimentin in all cases, while negative for TFE3, HMB45, desmin, CD34, and actin. The stroma was positive for vimentin, actin and focally for CD34, while negative for CK7, AMACR, TFE3, HMB45, and desmin. Estrogen and progesterone receptors were completely negative. FH and SDHB expression was retained in all analyzable cases. Proliferative index was barely detectable in stromal component and low in epithelial component, ranging 0 to 5% positive stained cells/high power field. Copy number variation was variable with no distinct pattern. No mutations in CDKN2A, BAP1, MET were detected. PRCC with MESTK-like features is a distinct variant of PRCC mimicking MESTK. Our findings add to the body of literature on ever expanding variants of PRCCs. Both epithelial and stromal components lacked true Müllerian features, which was also proven by immunohistochemistry.

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.

Papillary Renal Cell Carcinoma (PRCC): An Update

Papillary renal cell carcinoma (PRCC) is the second most common type of renal carcinoma following clear cell renal cell carcinoma. Papillary renal cell carcinoma is usually divided histologically into 2 types namely, type 1 and type 2. This classification, however, is unsatisfactory as many of papillary carcinoma are unclassifiable by the existing criteria. In recent years there has been a remarkable progress in our understanding of the molecular basis of PRCC. These studies have revealed that type 2 PRCCs represent a heterogenous group which may be subdivided into additional subtypes based on the genetic and molecular make up of these tumors and reflecting different clinical course and prognosis. Some of the molecular features such a hypermethylation of CPG islands in the promotor regions of genes and over expression of the antioxidant pathways within tumor cells have been recognized as markers of poor prognosis. Targeted therapies for papillary carcinoma in the past have been unsuccessful because of lack of clear understanding of the molecular basis of these tumors. It is hoped that recent progress in our understanding of the pathogenesis of various subtypes of PRCC, effective targeted therapies will eventually emerge in due course.

Chondroid and osseous metaplasia in an incidental type II papillary renal cell carcinoma with extensive solid areas: an unraveled molecular character

Chondroid and osseous metaplasia in a Type II Papillary renal cell carcinoma (PRCC) with extensive solid areas is a complex histological combination that has not been reported before. A 21 years old male presented with a comminuted fracture of right femur. On hematological investigations he was found to have low RBC count and hemoglobin. Radiological examination revealed an incidental, exophytic complex solid and cystic, mass lesion measuring 7 x 6.5 x 4.9 cm with thickened walls, septation and calcification. It was completely replacing upper pole of the left kidney with extension into perinephric fat. Enlarged para aortic and hilar nodes with necrosis were also noted. Radiological diagnosis was infectious processes such as tuberculosis versus malignancy. Surgical intervention comprising left partial nephrectomy was done. Histopathology and immunohistochemical analysis yielded the above diagnosis. Cytogenetic studies did not reveal gain of chromosome 7 and/or 17 or loss of chromosome Y, a characteristic genetic profile of PRCC. This case could be representative of a unique histological variant of PRCC in which the molecular profile yet needs to be unraveled.

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.

Warthin-like papillary renal cell carcinoma: Clinicopathologic, morphologic, immunohistochemical and molecular genetic analysis of 11 cases

Oncocytic papillary renal cell carcinoma (PRCC) is a distinct subtype of PRCC, listed as a possible new variant of PRCC in the 2016 WHO classification. It is composed of papillae aligned by large single-layered eosinophilic cells showing linearly arranged oncocytoma-like nuclei. We analyzed clinicopathologic, morphologic, immunohistochemical and molecular-genetic characteristics of 11 oncocytic PRCCs with prominent tumor lymphocytic infiltrate, morphologically resembling Warthin's tumor. The patients were predominantly males (8/11, 73%), with an average age of 59years (range 14-76), and a mean tumor size of 7cm (range 1-22cm). Tumors had the features of oncocytic PRCCs with focal pseudostratification in 8/11 cases and showed dense stromal inflammatory infiltration in all cases. Papillary growth pattern was predominant, comprising more than 60% of tumor volume. Tubular and solid components were present in 5 and 3 cases, respectively. Uniform immunohistochemical positivity was found for AMACR, PAX-8, MIA, vimentin, and OSCAR. Tumors were mostly negative for carboanhydrase 9, CD117, CK20, and TTF-1. Immunohistochemical stains for DNA mismatch repair proteins MLH1 and PMS2 were retained in all cases, while MSH2 and MSH6 were negative in 1 case. Tumor infiltrating lymphocytes (TILs) consisted of both B and T cells. Chromosomal copy number variation analysis showed great variability in 5 cases, ranging from a loss of one single chromosome to complex genome rearrangements. Only one case showed gains of chromosomes 7 and 17, among other aberrations. In 4 cases no numerical imbalance was found. Follow up data was available for 9 patients (median 47.6months, range 1-132). In 6 patients no lethal progression was noted, while 3 died of disease. In conclusion, Warthin-like PRCC is morphologically very close to oncocytic PRCC, from which it differs by the presence of dense lymphoid stroma. Chromosomal numerical aberration pattern of these tumors is variable; only one case showed gains of chromosomes 7 and 17. Warthin-like PRCC is a potentially aggressive tumor since a lethal outcome was recorded in 3/9 cases.