Renal cell carcinoma with areas mimicking renal angiomyoadenomatous tumor/clear cell papillary renal cell carcinoma

Clinicopathological and molecular features of renal cell carcinomas with haemangioblastoma-like features distinct from clear cell renal cell carcinoma

AIMS

Haemangioblastomas arise in the central nervous system. Rarely, haemangioblastomas may develop in extra-neural sites, such as the kidneys. A few reported cases of renal cell carcinomas (RCCs) with haemangioblastoma-like features have exhibited both clear cell renal cell carcinoma (CCRCC)- and haemangioblastoma-like components. The clinicopathological and molecular characteristics of RCCs with haemangioblastoma-like features were analysed, focusing on VHL alterations, in comparison with CCRCCs partially resembling haemangioblastoma.

METHODS AND RESULTS

Four RCCs with haemangioblastoma-like features and five CCRCCs partially resembling haemangioblastoma were included. The RCCs with haemangioblastoma-like features were indolent and lacked adverse prognostic factors. All RCCs with haemangioblastoma-like features had a well-circumscribed appearance and a thick fibromuscular capsule, with fibromuscular bundles extending into the tumour to varying degrees in the three tumours. Each RCC with haemangioblastoma-like features exhibited CCRCC-like areas with indistinct tubular structures and foci of haemangioblastoma-like areas, in which vessels and short spindle cells overwhelmed tumour cells. Whereas haemangioblastoma-like areas in the CCRCCs partially resembling haemangioblastoma exhibited sparse vessels and spindle cells and distinct clear cells. The RCCs with haemangioblastoma-like features exhibited a unique immunohistochemical profile, with positive staining for inhibin-α, S100, carbonic-anhydrase-9, keratin7, and high molecular weight keratin and negative staining for (alpha-methylacyl-CoA racemase) AMACR. RCC with haemangioblastoma-like features did not display any VHL alterations, including VHL mutation, 3p LOH, and methylation of the VHL promoter region, and the two tumours harboured a likely oncogenic missense variant of MTOR (c.7280T>G).

CONCLUSION

The histopathological, immunohistochemical, and molecular findings suggest that RCC with haemangioblastoma-like features is a distinct entity from CCRCC.

Renal angiomyoadenomatous tumor (RAT): a rare distinct entity with diagnostic challenges-a case report

BACKGROUND

Renal angiomyoadenomatous tumor (RAT) is a recently described rare renal neoplasm with variations in the presentation, gross, and microscopic findings, and having a benign course and good prognosis. It is characterized microscopically by the admixture of three components-epithelial cells arranged in tubules and nests, angiomyomatous stroma, and capillary-sized interconnecting vascular channels in close association with the epithelial cell clusters. Microscopically, these tumors can be confused with clear cell carcinoma, papillary carcinoma, mixed epithelial and stromal tumors, and angiomyolipoma. RAT differs from conventional clear cell carcinomas, which can rarely be associated with an identical leiomyomatosis stroma occasionally forming abortive vascular structures. RAT is a distinct morphologic entity, being different morphologically, immunohistochemically, and genetically from all renal tumors including conventional clear cell carcinoma and mixed epithelial and stromal tumor of the kidney.

CASE PRESENTATION

Here, we report a case of a 21-year-old man with renal angiomyoadenomatous tumor, a rare neoplasm with only a few previous cases reported in the literature. Unlike our case, most tumors have been identified in middle-aged males; they present as well-circumscribed, encapsulated tan-brown masses with variably prominent cystic areas.

CONCLUSION

Diagnosis of RAT is challenging because of the rarity of the disease and common presenting symptoms to other renal pathology and is supplemented with histopathology and immunohistochemistry. A multidisciplinary team approach for diagnosis and management along with long-term follow-up are warranted.

Clear cell papillary renal cell carcinoma: an update after 15 years

Fifteen years since the first recognition of clear cell papillary renal cell carcinoma, this distinct renal tumour type is now well accepted as a distinct entity in major classification schemes. It occurs both with and without end-stage renal disease and may be multifocal or bilateral in both scenarios. Recognisable morphological features include clear cells lining branching glands and variable papillary formations with nuclear alignment. Most tumours are small (pT1a) and nucleolar grade 1-2. Immunohistochemistry consistently shows positivity for carbonic anhydrase IX and cytokeratin 7, and often high molecular weight cytokeratin or GATA3, the latter suggesting distal nephron phenotype. Labeling for AMACR and CD10 is consistently negative or minimal. Despite a resemblance to clear cell renal cell carcinoma, molecular alterations of VHL and chromosome 3p are typically lacking, with debatable rare exceptions. Potential mimics include clear cell renal cell carcinoma (with branching architecture or nuclear alignment), papillary renal cell carcinoma with clear cytoplasm, or rarely MITF family translocation renal cell carcinoma. Clinical behaviour is highly favourable with rare, debatable reports of aggressive behaviour. Combined with striking similarity to several extrarenal benign neoplasms, it would be reasonable to reclassify this entity as a benign or low malignant potential neoplasm. Using the nomenclature of the extrarenal counterparts, clear cell papillary (cyst)adenoma is proposed.

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.

Renal Cell Carcinoma with Clear Cell Papillary Features: Perspectives of a Differential Diagnosis

Thirty-one cases of low-grade renal cell carcinoma (RCC) with clear cells and tubulopapillary/papillary architecture were analyzed retrospectively with immunohistochemical and genetic markers to gain more experience with the differential diagnosis of such cases. All samples coexpressed CK7 and CA9; the TFE3 or TFEB reactions were negative; the CD10 and the AMACR stainings were negative in 27 cases and 30 cases, respectively. The FISH assays for papillary RCC, available in 27 cases, and deletion of chromosome 3p, available in 29 cases, gave negative results. The results for 3p deletion, VHL gene mutation or VHL gene promoter region hypermethylation testing, along with the diffuse CD10-positivity in 2 cases confirmed 21 cases as clear cell papillary RCC (CCPRCC; CK7+, CA9+; no 3p loss, no VHL abnormality) and 10 cases as clear cell RCC (CCRCC; CK7+, CA9+; no 3p loss, VHL abnormality mutation/hypermethylation present). In CCPRCCs, the representative growth pattern was branching tubulo-acinar, commonly accompanied by cyst formation. The linear nuclear arrangement or cup-shaped staining of CA9 did not necessarily indicate CCPRCC, and the absence of these did not exclude the diagnosis of CCPPRC. One tumor infiltrated the renal sinus; the others exhibited pT1 stage; and metastatic outcome was not recorded. The CCRCC cases were in pT1 stage; 6 exhibited cup-shaped staining of CA9, and 1 displayed lymph node metastasis at the time of surgery. Distant metastatic disease was not observed. In summary, the VHL abnormalities distinguished the subset of CCRCC with diffuse CK7-positivity and no 3p loss from cases of CCPRCC.

Clear cell renal cell carcinoma with wild-type von Hippel-Lindau gene: a non-existent or new tumour entity?

The current World Health Organisation (WHO) classification of renal tumours is based on characteristic histological features or specific molecular alterations. von Hippel-Lindau (VHL) alteration is the hallmark of clear cell renal cell carcinoma (RCC). After identification of the MiT translocation family of tumours, clear cell papillary renal cancer and others, the group of ccRCC with wild-type VHL is small. TCEB1 mutation combined with chromosome 8q loss is an emerging tumour entity with wild-type VHL. Inactivation of TCEB1 increases HIF stabilisation via the same mechanism as VHL inactivation. Importantly, recent molecular analyses suggest the existence of another 'VHL wild-type' evolutionary subtype of clear cell RCC in addition to TCEB1 mutated RCC and clear cell papillary renal cancer. These tumours are characterised by an aggressive behaviour, high tumour cell proliferation rate, elevated chromosomal instability and frequent presence of sarcomatoid differentiation. Future clinicopathological studies will have to provide data to determine whether TCEB1 tumours and clear cell RCC with wild-type VHL are separate tumour entities or represent variants of a clear cell RCC tumour family.

Reactivity of CK7 across the spectrum of renal cell carcinomas with clear cells

AIMS

Current available data on cytokeratin 7 (CK7) immunostaining pattern in the clear cell renal cell carcinoma (RCC) spectrum is conflicting. The aim of this study was to assess CK7 immunoreactivity within the spectrum of clear cell renal neoplasms, including clear cell RCC, multicystic renal neoplasm of low malignant potential and clear cell papillary RCC-like tumours.

METHODS AND RESULTS

We analysed two clones of CK7 and two tumour blocks for a total of 75 cases divided into five distinct groups: (i) low-grade clear cell RCC, (ii) high-grade clear cell RCC, (iii) multicystic renal neoplasm of low malignant potential, (iv) clear cell RCC with cystic changes and (v) clear cell papillary RCC-like tumours. We found the highest CK7 reactivity in low-grade clear cell RCC, multicystic renal neoplasm of low malignant potential and clear cell papillary RCC-like groups, ranging from 60% to 93%.

CONCLUSIONS

Our findings show that CK7 immunoreactivity in clear cell RCC is variable, and the extent of staining depends on the grade and architectural growth patterns of the tumours.

Renal angiomyoadenomatous tumour

Renal angiomyoadenomatous tumour is a newly described rare neoplasm. This tumour is characterised microscopically by admixture of three components- epithelial cells arranged in tubules and nests, angiomyomatous stroma and capillary sized interconnecting vascular channels in close association with the epithelial cell clusters. Microscopically it has wide range of differential diagnoses which include mixed epithelial and stromal tumour of kidney, angiomyolipoma and clear cell renal cell carcinoma with angiomyolipomatous/angiomyoadenomatous areas. Renal angiomyoadenomatous tumour should be differentiated from these tumours. Till now, only 10 cases have been reported in English medical literature. Here, we are reporting a case of renal angiomyoadenomatous tumour in a 29 year- old female patient who presented with hematuria and low backache and describing its main features so as to differentiate this entity from other renal tumours. To the best of our knowledge, this is the first case to be reported from India.

A contemporary series of renal masses with emphasis on recently recognized entities and tumors of low malignant potential: A report based on 624 consecutive tumors from a single tertiary center

INTRODUCTION

A number of new renal tumor entities have been recognized by the 2016 World Health Organization classification of urologic tumors. The classification includes tumors with different behavior and introduces one tumor with low malignant potential, the multilocular cystic clear cell renal cell neoplasm of low malignant potential (mcCCRCNLMP). However, some categories still labeled as "carcinoma", such as clear cell papillary renal cell carcinoma (CCPRCC), renal angioleiomyomatous tumor (RAT), and tubulocystic carcinoma (TCRCC), all with a particularly good prognosis when diagnosed as low stage, show no malignant behavior: in fact, no metastases have been reported in these categories when surgically excised. Current experience is limited to supporting these neoplasms as benign entities although, recent literature data is defining these entities as "low malignant potential tumors".

MATERIAL AND METHODS

We conducted a search through our files on a consecutive series of 624 renal tumors diagnosed over a period of 2 years to address the incidence of this category of tumors.

RESULTS

Applying strict histological criteria, the "low malignant potential" tumors, comprised 7% of renal masses that are less than 4cm in size and 3.8% of renal masses measuring 4-7cm in the series of 624 renal tumors. When benign tumors are taken into considerations, the benign and "low malignant potential tumors" represent about one third of renal masses <4cm and one sixth of renal masses between 4 and 7cm. All these cases have not shown recurrence or metastasis at follow-up, mean follow-up of 18 months (range 6-30 months).

CONCLUSIONS

This information may assist urologists in developing guidelines for counseling and proper clinical management for patients with "low malignant potential" tumors or small renal masses.

Validation of 34betaE12 immunoexpression in clear cell papillary renal cell carcinoma as a sensitive biomarker

Clear cell papillary renal cell carcinoma (CCPRCC) is a recently recognised neoplasm with a broad spectrum of morphological characteristics, thus representing a challenging differential diagnosis, especially with the low malignant potential multicystic renal cell neoplasms and clear cell renal cell carcinoma. We selected 14 cases of CCPRCC with a wide spectrum of morphological features diagnosed on morphology and CK7 immunoreactivity and analysed them using a panel of immunohistochemical markers, focusing on 34βE12 and related CKs 1,5,10 and 14 and several molecular analyses such as fluorescence in situ hybridisation (FISH), array comparative genomic hybridisation (aCGH), VHL methylation, VHL and TCEB1 sequencing and multiplex ligation-dependent probe amplification (MLPA). Twelve of 13 (92%) CCPRCC tumours were positive for 34βE12. One tumour without 3p alteration by FISH revealed VHL mutation and 3p deletion at aCGH; thus, it was re-classified as clear cell RCC. We concluded that: (1) immunohistochemical expression of CK7 is necessary for diagnostic purposes, but may not be sufficient to identify CCPRCC, while 34βE12, in part due to the presence of CK14 antigen expression, can be extremely useful for the recognition of this tumour; and (2) further molecular analysis of chromosome 3p should be considered to support of CCPRCC diagnosis, when FISH analysis does not evidence the common loss of chromosome 3p.

Renal Neoplasms With Overlapping Features of Clear Cell Renal Cell Carcinoma and Clear Cell Papillary Renal Cell Carcinoma: A Clinicopathologic Study of 37 Cases From a Single Institution

Clear cell papillary renal cell carcinoma (CCPRCC) was recently included in the International Society of Urological Pathology Vancouver Classification of Renal Neoplasia as a subtype of RCC that is morphologically, immunohistochemically, and genetically distinct from both clear cell renal cell carcinoma (CCRCC) and papillary renal cell carcinoma. In our clinical practice we have observed tumors with overlapping histologic features of CCPRCC and CCRCC; therefore, our aim was to describe the morphologic, immunohistochemical, and clinical characteristics of these tumors. We examined a large series of consecutive nephrectomies diagnosed as CCRCC and found 37 tumors with morphologic overlap between CCRCC and CCPRCC, identifying 2 patterns. Pattern 1 tumors (N=19) had areas diagnosable as CCRCC admixed with foci having a prominent linear arrangement of nuclei away from the basement membrane imparting a resemblance to CCPRCC; however, other morphologic features commonly seen in CCPRCC (such as branching acini and cystic spaces with papillary tufts) were not typical and, when present, were focal or poorly developed. Pattern 2 (N=18) tumors had 2 discrete areas, one area with an appearance strongly resembling CCPRCC and the other with higher grade nuclei and features diagnosable as CCRCC, sometimes including rhabdoid differentiation, sarcomatoid differentiation, necrosis, and high-stage disease. Four (21%) of the pattern 1 tumors had grade 3 nuclei in the CCRCC-like areas, and 4 were high stage (pT3a). Of the 16 immunostained pattern 1 tumors, all expressed cytokeratin 7 (CK7) at least focally in the CCPRCC-like areas, strongly and diffusely in 9 (56%) cases; 12 (75%) showed negative to focal and/or weak CK7 expression in the CCRCC-like areas. CD10, α-methylacyl-CoA-racemase, high-molecular-weight cytokeratin, and carbonic anhydrase IX (CA IX) had no significant differential expression between these foci. No cup-like staining pattern was seen with CA IX. Two (11%) patients with pattern 1 tumors developed metastases, and 1 (5%) subsequently died of disease. Eleven (61%) pattern 2 cases had the International Society of Urological Pathology grade 3 nuclei in the CCRCC-like areas, and 7 (39%) were grade 4 (4 of these cases had rhabdoid features; 1 was also sarcomatoid). Of the 16 immunostained pattern 2 tumors, 8 (50%) showed strong diffuse CK7 expression in the CCPRCC-like areas, and 9 (56%) showed complete lack of CK7 expression in the CCRCC-like areas. CD10, α-methylacyl-CoA-racemase, and high-molecular-weight cytokeratin did not have significant differential expression. Membranous expression of CA IX, typically strong and diffuse, was identified in both the CCPRCC-like and CCRCC-like areas in all cases tested (with a cup-like pattern at least focally in the CCPRCC-like areas of 10 [63%] pattern 2 cases). Five (28%) patients with pattern 2 tumors had distant metastases, 3 (17%) of whom subsequently died of disease. Renal cell carcinomas with areas resembling both CCRCC and CCPRCC occur. Some can have high-grade and high-stage foci, and aggressive clinical outcomes are seen. Given this malignant potential, we would presently diagnose such cases as CCRCC. These 2 patterns of renal neoplasia underscore the need for caution in diagnosing CCPRCC on limited sampling, reserving the diagnosis for those tumors that strictly fulfill both morphologic and immunohistochemical criteria.

Clear cell papillary renal cell carcinoma and renal angiomyoadenomatous tumor: two variants of a morphologic, immunohistochemical, and genetic distinct entity of renal cell carcinoma

Clear cell papillary renal cell carcinoma (ccpRCC) and renal angiomyoadenomatous tumor (RAT) share morphologic similarities with clear cell (ccRCC) and papillary RCC (pRCC). It is a matter of controversy whether their morphologic, immunophenotypic, and molecular features allow the definition of a separate renal carcinoma entity. The aim of our project was to investigate specific renal immunohistochemical biomarkers involved in the hypoxia-inducible factor pathway and mutations in the VHL gene to clarify the relationship between ccpRCC and RAT. We investigated 28 ccpRCC and 9 RAT samples by immunohistochemistry using 25 markers. VHL gene mutations and allele losses were investigated by Sanger sequencing and fluorescence in situ hybridization. Clinical follow-up data were obtained for a subset of the patients. No tumor recurrence or tumor-related death was observed in any of the patients. Immunohistochemistry and molecular analyses led to the reclassification of 3 tumors as ccRCC and TFE3 translocation carcinomas. The immunohistochemical profile of ccpRCC and RAT samples was very similar but not identical, differing from both ccRCC and pRCC. Especially, the parafibromin and hKIM-1 expression exhibited differences in ccpRCC/RAT compared with ccRCC and pRCC. Genetic analysis revealed VHL mutations in 2/27 (7%) and 1/7 (14%) ccpRCC and RAT samples, respectively. Fluorescence in situ hybridization analysis disclosed a 3p loss in 2/20 (10%) ccpRCC samples. ccpRCC and RAT have a specific morphologic and immunohistochemical profile, but they share similarities with the more aggressive renal tumors. On the basis of our results, we regard ccpRCC/RAT as a distinct entity of RCCs.

Clear cell-papillary renal cell carcinoma of the kidney not associated with end-stage renal disease: clinicopathologic correlation with expanded immunophenotypic and molecular characterization of a large cohort with emphasis on relationship with renal angiomyoadenomatous tumor

Clear cell-papillary renal cell carcinoma (CC-Pap RCC) is a recently described renal tumor initially reported in the setting of end-stage renal disease (ESRD). It has unique morphologic and immunohistochemical features that differentiate it from the more common clear cell RCC and papillary RCC. Recently, these tumors have also been described in a sporadic setting. We studied 64 cases of CC-Pap RCC not associated with ESRD (57 CC-Pap RCCs and 7 cases with features of renal angiomyoadenomatous tumors [RAT] including 5 initially diagnosed as such). The morphologic features of all cases and the immunohistochemical profile of 59 cases were studied along with the clinical and molecular features of 30 and 12 cases, respectively. All the tumors were well circumscribed with a mean tumor size of 2.6 cm and showed a wide array of architectural patterns, usually mixed, including tubular (77%), papillary (62%), tubulocystic (52%), and compact nested (21%). Seventy-three percent of the cases showed areas in which the tumor nuclei had a distinct orientation away from the basement membrane. Ninety-two percent of the cases had a low Fuhrman nuclear grade (nuclear grade 2%-86%, and nuclear grade 1%-6%); however, 8% cases showed foci of Fuhrman nuclear grade 3. In 4 cases, epithelial tumor comprised <5% of the tumor; >95% of the tumor was cystic or hyalinized. The stroma varied from being minimal to occasionally prominent myxoid to hyalinized and rarely with organized amianthoid fibers or well-defined smooth muscle bundles. Pathologic stage was reliably assigned in 60 cases, of which 93.3% (56 cases) were pT1, 3.3% (2 cases) were pT2, and 3.3% (2 cases) were pT3a with extension into the perinephric fat. One case had coagulative necrosis; sarcomatoid change and vascular invasion was not identified. The tumors showed a fairly typical immunoprofile characterized by positivity for CK7 (100%), HMCK (96%), CAIX (94%), and vimentin (100%) with negativity for AMACR, RCC, and TFE3; CD10 was positive in 24%. None of the cases tested showed recurrent chromosomal imbalances by virtual karyotyping, fluorescence in situ hybridization, or 3p loss of heterozygosity analysis. VHL gene mutations were, however, noted in 3 cases (2 in exon 1 and 1 in exon 3). Clinical follow-up information was available in 47% of the patients, with a mean and median follow-up of 47 and 37 months, respectively (range, 18 to 108 mo). One case occurred in the setting of VHL syndrome and multiple benign cysts. None of the cases showed local recurrence, metastasis, or death due to disease. Morphology, immunophenotype, and molecular studies did not vary between typical cases, those with prominent smooth muscle (so-called RAT), and historically published data on cases occurring in ESRD. Our analysis confirms that CC-Pap RCC is a unique subtype of adult renal epithelial neoplasia in which tumors are frequently small, are of low nuclear grade and pathologic stage, and have extremely favorable short to intermediate range prognosis. Tumors occurring sporadically, with prominent smooth muscle stroma (so-called RAT), and occurring in ESRD are in the spectrum of the same category of tumors.

Papillary or pseudopapillary tumors of the kidney

Papillary architecture is one of the most common morphological patterns in renal cell neoplasms. Many renal cell neoplasms can also exhibit, diffusely or focally, papillary growth pattern. This article reviews all the renal cell neoplasms with papillary or pseudopapillary architecture, with an emphasis on recently described new histological types. New insights into the "old" entities, including their immunohistochemical and genetic features, will also be discussed.

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.

Renal cell carcinoma with angioleiomyoma-like stroma: clinicopathological, immunohistochemical, and molecular features supporting classification as a distinct entity

Rare renal epithelial neoplasms have been recognized to have an angioleiomyoma or leiomyoma-like proliferation of stromal smooth muscle; however, the nature of these tumors and their relationships to other renal cell carcinomas are poorly understood. We analyzed 23 such tumors for their clinicopathological, immunohistochemical, and cytogenetic features using fluorescence in situ hybridization. Twelve showed a homogeneous combination of features and were reclassified as renal cell carcinoma with angioleiomyoma-like stroma. These were composed of neoplastic glandular structures lined by cells with mixed clear, pale, and eosinophilic cytoplasm forming occasional papillary tufts. The stroma resembled smooth muscle and often extended away from the epithelial component, entrapping perinephric fat or non-neoplastic renal elements. Immunohistochemistry showed the epithelium to have reactivity for: carbonic anhydrase IX, CD10, vimentin, cytokeratin 7, cytokeratin 34βE12, and PAX8 but not α-methylacyl-coA-racemase. The stroma labeled for smooth muscle (smooth muscle actin 3+, desmin 1+, caldesmon 3+) but not epithelial antigens. Neither component showed substantial reactivity for HMB45, melan-A, cathepsin K, or TFE3 protein. An interrupted, conspicuous layer of CD34-positive endothelial cells rimmed the epithelium, imparting a two-cell layer pattern resembling myoepithelial or basal cells. Chromosome 3p deletion and trisomy 7 and 17 were uniformly absent. Follow-up was available for three patients, none of whom experienced malignant behavior. Eleven tumors were excluded from this category and considered to be clear cell renal cell carcinoma with a reactive proliferation of smooth muscle (n=4) or tangential sectioning of the pseudocapsule (n=2), renal cell carcinoma unclassified (n=4), or clear cell papillary renal cell carcinoma (n=1). In summary, renal cell carcinoma with angioleiomyoma-like stroma is a distinct neoplasm with characteristic morphological, immunohistochemical, and molecular features, unrelated to clear cell renal cell carcinoma. The immunoprofile overlaps partly with that of clear cell papillary renal cell carcinoma, though morphology and reactivity for CD10 are points of contrast.

Clear cell papillary renal cell carcinoma is an indolent and low-grade neoplasm with overexpression of cyclin-D1

AIMS

Several entities have been individualized recently within the family of renal neoplasms with papillary features. Clear cell papillary renal cell carcinoma (CCPRCC) was first described in patients with end-stage renal disease, but is also observed in patients with normal renal function. The objective of this study was to document the clinicopathological and immunohistochemical characteristics of CCPRCC, with a special emphasis on cyclin D1 expression.

METHODS AND RESULTS

The patients were 25 men and 17 women, mean age 60.7 years. Seventeen patients had a chronic renal disease. All tumours were stage pT1, with a mean diameter of 2 cm. Six tumours were multifocal. Tumours cells were mainly cuboidal, with clear cytoplasm and low-grade nuclei apically aligned. In all cases, Fuhrman nuclear grade was one or two. No necrosis or vascular invasion was seen. During follow-up (10-72 months), no metastasis or death related to the disease was observed. Immunohistochemistry showed strong and diffuse cytokeratin 7 immunoreactivity in all cases, but no labelling for AMACR or TFE3. There was diffuse nuclear cyclin D1 immunoreactivity in 83% of cases.

CONCLUSION

CCPRCC is now a well-characterized entity. This tumour is an indolent and very low-grade neoplasm. Here we report the first study, to our knowledge, demonstrating the overexpression of cyclin D1 immunostaining by this tumour.