Eosinophilic, Solid, and Cystic Renal Cell Carcinoma: Clinicopathologic Study of 16 Unique, Sporadic Neoplasms Occurring in Women

ESC, ALK, HOT and LOT: Three Letter Acronyms of Emerging Renal Entities Knocking on the Door of the WHO Classification

Kidney neoplasms are among the most heterogeneous and diverse tumors. Continuous advancement of this field is reflected in the emergence of new tumour entities and an increased recognition of the expanding morphologic, immunohistochemical, molecular, epidemiologic and clinical spectrum of renal tumors. Most recent advances after the 2016 World Health Organization (WHO) classification of renal cell tumors have provided new evidence on some emerging entities, such as anaplastic lymphoma kinase rearrangement-associated RCC (ALK-RCC), which has already been included in the WHO 2016 classification as a provisional entity. Additionally, several previously unrecognized entities, not currently included in the WHO classification, have also been introduced, such as eosinophilic solid and cystic renal cell carcinoma (ESC RCC), low-grade oncocytic renal tumor (LOT) and high-grade oncocytic renal tumor (HOT) of kidney. Although pathologists play a crucial role in the recognition and classification of these new tumor entities and are at the forefront of the efforts to characterize them, the awareness and the acceptance of these entities among clinicians will ultimately translate into more nuanced management and improved prognostication for individual patients. In this review, we summarise the current knowledge and the novel data on these emerging renal entities, with an aim to promote their increased diagnostic recognition and better characterization, and to facilitate further studies that will hopefully lead to their formal recognition and consideration in the future classifications of kidney tumors.

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.

Somatic Mutations of TSC2 or MTOR Characterize a Morphologically Distinct Subset of Sporadic Renal Cell Carcinoma With Eosinophilic and Vacuolated Cytoplasm

The differential diagnosis of renal cell neoplasms with solid or nested architecture and eosinophilic cytoplasm has become increasingly complex. Despite recent advances in classifying a number of entities exhibiting this morphology, some tumors remain in the unclassified category. Here we describe a morphologically distinct group of sporadic renal cell carcinoma (RCC) with predominantly nested architecture, eosinophilic, and remarkably vacuolated cytoplasm retrospectively identified from a cohort of previously unclassified tumors. We examined the clinicopathologic and immunohistochemical features of these tumors and investigated their mutational and copy number alterations using a targeted next-generation sequencing platform. The study included 7 patients with a mean age of 54 years (range: 40 to 68 y) and a male to female ratio of 3:4. All patients presented with a solitary renal mass and had no prior medical or family history raising concern for syndromic conditions. Tumors were well-circumscribed, unencapsulated, and comprised of nests of eosinophilic cells in a hypocellular and often edematous stroma. Tumor cells had round nuclei with prominent nucleoli and granular cytoplasm with striking vacuolization. Thick-walled vessels and calcifications were also frequently present, whereas increased mitotic activity, necrosis, foamy histiocytes or lymphocytic infiltrates were not identified. All cases were positive for PAX8, had retained expression of SDHB and FH, and exhibited a CK7-/CK20- phenotype. While cathepsin-K was positive in 5 cases, none exhibited immunoreactivity to HMB45 or Melan A, or TFE3 immunostaining. Next-generation sequencing identified somatic inactivating mutations of TSC2 (3/5 tumors tested) or activating mutations of MTOR (2/5) as the primary molecular alterations, consistent with hyperactive mTOR complex 1 signaling which was further demonstrated by phospho-S6 and phospho-4E-BP1 immunostaining. Copy number analysis revealed a loss of chromosome 1 in both cases with MTOR mutation. These tumors represent a novel subset of sporadic RCC characterized by alterations in TSC1-TSC2 complex or the mTOR complex 1 pathway. Recognition of their characteristic morphologic and immunophenotypic features will allow them to be readily identified and separated from the unclassified RCC category.

Five decades of urologic pathology: the accelerating expansion of knowledge in renal cell neoplasia

Those who are knowledgeable in cosmology inform us that the expansion of the universe is such that the velocity at which a distant galaxy is receding from the observer is continually increasing with time. We humbly paraphrase that as "The bigger the universe gets, the faster it gets bigger." This is an interesting analogy for the expansion of knowledge in the field of renal tumor pathology over the past 30 to 50 years. It is clear that a multitude of dedicated investigators have devoted incalculable amounts of time and effort to the pursuit of knowledge about renal epithelial neoplasms. As a consequence of the contributions of numerous investigators over many decades, the most recent World Health Organization classification of renal neoplasms includes about 50 well defined and distinctive renal tumors, as well as various miscellaneous and metastatic tumors. In addition, a number of emerging or provisional new entities are under active investigation and may be included in future classifications. In this review, we will focus on a number of these tumors, tracing as accurately as we can the origins of their discovery, relating relevant additions to the overall knowledge base surrounding them, and in some instances addressing changes in nomenclature.

Eosinophilic Kidney Tumors: Old and New

Context.—

Eosinophilic cytoplasm is the most common finding of difficult-to-classify kidney tumors. Morphology, cytogenetics, and immunohistochemical stains are discriminatory. This review compares well-recognized tumors such as granular clear cell carcinoma, papillary variants, chromophobe renal cell carcinoma, and oncocytoma and introduces newly described entities of hybrid oncocytic tumors, carcinomas defined by translocations, and carcinomas with deficiencies in the tricarboxylic acid cycle. The focus is on immunostaining, clinical correlations, and differential diagnoses. Representative examples of some entities are presented with elaboration on their workup.

Objective.—

To provide a review of the differential diagnoses for renal neoplasms with eosinophilic cytoplasm and elaborate on methods that may assist with correct identification.

Data Sources.—

Review of current literature on kidney tumors with eosinophilic cytoplasm, as well as the authors' personal experience.

Conclusions.—

Eosinophilic cytoplasm is a feature shared by many kidney tumors. Understanding the morphologic differences and the role of ancillary studies is key when encountering such a tumor.

Are Sporadic Eosinophilic Solid and Cystic Renal Cell Carcinomas Characterized by Somatic Tuberous Sclerosis Gene Mutations?

Eosinophilic solid and cystic renal cell carcinomas (ESC RCC) is a rare, unique tumor type not yet included in the World Health Organization classification of renal neoplasia. Separately, RCCs found in patients with tuberous sclerosis complex (TSC) have recently been categorized into 3 morphologic groups: RCC with a tubulopapillary architecture separated by smooth muscle stroma, chromophobe-like, and eosinophilic-microcytic type. The third classification has been identified in ∼11% of TSC-associated RCC and have histology identical to ESC RCCs. The sporadic form of ESC RCC, not associated with TSC, have only been characterized on the cytogenetic level and the full molecular underpinnings have yet to be examined. Using next-generation sequencing we present 2 cases of sporadic ESC RCC in patients without clinical features of tuberous sclerosis, which demonstrate pathogenic somatic TSC2 gene mutations. These mutations are without other alterations in any other genes associated with RCC, suggesting that sporadic ESC RCC may be characterized by somatic tuberous sclerosis gene mutations (TSC2).

Concurrent Eosinophilic Solid and Cystic Renal Cell Carcinoma and Angiomyolipoma With Epithelial Cysts in the Setting of Tuberous Sclerosis Complex: A Rare Synchronous Occurrence of 2 Distinct Entities

Eosinophilic solid and cystic renal cell carcinoma (ESCRCC) is a recently described distinct renal neoplasm known to occur almost exclusively in female patients with or without tuberous sclerosis complex (TSC). We report a case of ESCRCC with 2 synchronous angiomyolipomas, including 1 angiomyolipoma with epithelial cysts (AMLEC), a rare cystic variant of AML that typically arises sporadically in the absence of TSC, in a 46-year-old woman with TSC. Besides additional copy number alterations identified in ESCRCC via molecular karyotyping, we also report a unique histologic feature of TSC-associated ESCRCC previously not described in detail, with formation of semicircular multinucleated neoplastic giant cells engulfing an additional intact neoplastic cell, simulating emperipolesis. To the best of our knowledge, this is the first reported case of ESCRCC with concurrent AMLEC in a patient with TSC, confirmed through additional genetic testing showing a germline heterozygous mutation in TSC1. Awareness of ESCRCC helps avoid the pitfall of a diagnosis of unclassified renal cell carcinoma, a typically much more aggressive tumor.

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.

New entities, new technologies, new findings: A review of the cytologic features of recently established subtypes of renal cell carcinoma

Several new renal tumor types with distinctive pathologic, epidemiologic, and genetic signatures have recently been adopted in the fourth edition of the World Health Organization classification. In succeeding years, the cytologic features of most of these new types have been described, adding to the trend of increasing diagnostic accuracy for most common renal cell carcinoma subtypes and the important diagnostic role of cytologic sampling in the management and personalization of therapy. The current article reviews the cytologic findings from these recently established renal cell carcinoma subtypes. Emphasis is placed on cytologic diagnostic clues, confirmatory ancillary testing, salient differential diagnoses, and challenges that can be encountered in an attempt to render accurate interpretations in small samples.

Renal oncocytoma with vascular and perinephric fat invasion

Renal oncocytoma is a benign epithelial neoplasm typically composed of large cells with granular eosinophilic cytoplasm. Although rare, histologically worrisome features such as vascular and perinephric fat invasion have been reported. Of the 159 renal oncocytomas resected at our institution, 20 (12.6%) had vascular and/or perinephric fat invasion. Microscopically, 10 oncocytomas had perinephric fat invasion, 7 had vascular invasion and 3 had both vascular and perinephric fat invasion. Grossly, perinephric fat invasion was visible in three cases and tumour was identified within the branches of the renal vein in two cases. Tumours occurred in 14 men and 6 women (M:F = 2.3:1). The mean age at diagnosis was 64.5 years (range, 33-88 years). A total of 11 cases had radical nephrectomies while 9 cases had partial nephrectomies. There was no evidence of disease recurrence, metastasis or death due to tumour after a mean follow up of 25.6 months (range, 2-103 months). The presence of vascular and perinephric fat invasion in renal oncocytoma though worrisome, does not alter the benign course of the tumour.

WHO/ISUP classification, grading and pathological staging of renal cell carcinoma: standards and controversies

PURPOSE

Pathological parameters assessed on biopsies and resection specimens have a pivotal role in the diagnosis, prognosis and management of patients with renal cell carcinoma (RCC).

METHODS

A non-systematic literature search was performed, updated to January 2018, to identify key standards and controversies in the pathological classification, grading and staging of RCC.

RESULTS

Although most RCCs exhibit characteristic morphology that enables easy categorisation, RCCs show considerable morphological heterogeneity and it is not uncommon for there to be difficulty in assigning a tumour type, especially with rarer tumour subtypes. The differentiation between benign and malignant oncocytic tumours remains a particular challenge. The development of additional immunohistochemical and molecular tests is needed to facilitate tumour typing, because of the prognostic and therapeutic implications, and to enable more reliable identification of poorly differentiated metastatic tumours as being of renal origin. Any new tests need to be applicable to small biopsy samples, to overcome the heterogeneity of renal tumours. There is also a need to facilitate identification of tumour types that have genetic implications, to allow referral and management at specialist centres. Digital pathology has a potential role in such referral practice.

CONCLUSION

Much has been done to standardise pathological assessment of renal cell carcinomas in recent years, but there still remain areas of difficulty in classification and grading of these heterogeneous tumours.

Recognizing Hereditary Renal Cancers Through the Microscope: A Pathology Update

A heightened understanding of hereditary renal cancer syndromes and their molecular basis has led to an increased awareness and recognition of these renal neoplasms by pathologists. Because a diagnosis of hereditary renal cell carcinoma has a profound impact on the patient and family members, when and how to raise such a suspicion via pathologic assessment has become an important yet very challenging task. This review discusses key clinicopathologic, immunohistochemical, and genetic characteristics of hereditary renal cancer syndromes, and important differential diagnostic challenges, emphasizing recent pathologic and molecular advances.

"High-grade oncocytic renal tumor": morphologic, immunohistochemical, and molecular genetic study of 14 cases

The spectrum of the renal oncocytic tumors has been expanded in recent years to include several novel and emerging entities. We describe a cohort of novel, hitherto unrecognized and morphologically distinct high-grade oncocytic tumors (HOT), currently diagnosed as "unclassified" in the WHO classification. We identified 14 HOT by searching multiple institutional archives. Morphologic, immunohistochemical (IHC), molecular genetic, and molecular karyotyping studies were performed to investigate these tumors. The patients included 3 men and 11 women, with age range from 25 to 73 years (median 50, mean 49 years). Tumor size ranged from 1.5 to 7.0 cm in the greatest dimension (median 3, mean 3.4 cm). The tumors were all pT1 stage. Microscopically, they showed nested to solid growth, and focal tubulocystic architecture. The neoplastic cells were uniform with voluminous oncocytic cytoplasm. Prominent intracytoplasmic vacuoles were frequently seen, but no irregular (raisinoid) nuclei or perinuclear halos were present. All tumors demonstrated prominent nucleoli (WHO/ISUP grade 3 equivalent). Nine of 14 cases were positive for CD117 and cytokeratin (CK) 7 was either negative or only focally positive in of 6/14 cases. All tumors were positive for AE1-AE3, CK18, PAX 8, antimitochondrial antigen, and SDHB. Cathepsin K was positive in 13/14 cases and CD10 was positive in 12/13 cases. All cases were negative for TFE3, HMB45, Melan-A. No TFEB and TFE3 genes rearrangement was found in analyzable cases. By array CGH, complete chromosomal losses or gains were not found in any of the cases, and 3/9 cases showed absence of any abnormalities. Chromosomal losses were detected on chromosome 19 (4/9), 3 with losses of the short arm (p) and 1 with losses of both arms (p and q). Loss of chromosome 1 was found in 3/9 cases; gain of 5q was found in 1/9 cases. On molecular karyotyping, 3/3 evaluated cases showed loss of heterozygosity (LOH) on 16p11.2-11.1 and 2/3 cases showed LOH at 7q31.31. Copy number (CN) losses were found at 7q11.21 (3/3), Xp11.21 (3/3), Xp11.22-11.21 (3/3), and Xq24-25 (2/3). CN gains were found at 13q34 (2/3). Ten patients with available follow up information were alive and without disease progression, after a mean follow-up of 28 months (1 to 112 months). HOT is a tumor with unique morphology and its IHC profile appears mostly consistent. HOT should be considered as an emerging renal entity because it does not meet the diagnostic criteria for other recognized eosinophilic renal tumors, such as oncocytoma, chromophobe renal cell carcinoma (RCC), TFE3 and TFEB RCC, SDH-deficient RCC, and eosinophilic solid and cystic RCC.

Evaluation of diagnostic accuracy and a practical algorithmic approach for the diagnosis of renal masses by FNA

BACKGROUND

The classification of renal neoplasms is essential for oncologic risk stratification and clinical management, and an accurate pretreatment pathologic diagnosis can provide useful guidance for active surveillance, minimally invasive ablative therapy, or surgical resection and can reduce the incidence of overtreatment. Previous studies evaluating the diagnostic accuracy of fine-needle aspiration (FNA) and core-needle biopsy (CNB) for renal masses are limited and show variable results.

METHODS

Two hundred forty-seven renal FNA cases with or without concurrent CNB performed and/or reviewed at the Stanford University School of Medicine over the course of 20 years were identified. Cytohistopathologic correlation was performed for 77 cases with subsequent resection specimens. All available case materials were reviewed, and select cases were worked up further and reclassified as necessary.

RESULTS

Cytohistopathologic correlation showed 96% diagnostic specificity and 83% sensitivity for renal FNA with or without concurrent CNB. Discordant cases were mostly attributed to sampling errors or suboptimal specimens (79%) and also included 2 non-renal cell carcinoma entities (1 case of angiomyolipoma and 1 case of a benign peripheral nerve sheath tumor) and 1 case involving misclassification of the renal cell carcinoma subtype.

CONCLUSIONS

There is considerable value in FNA/CNB for the initial diagnosis of renal masses because of the high diagnostic specificity and sensitivity. Sensitivity is predominantly dependent on sufficient sampling, and additional potential diagnostic pitfalls include nonepithelial and rare entities. Judicious use of ancillary techniques is encouraged, especially when one is presented with a limited specimen, and this article presents a practical algorithmic approach to the diagnosis of renal masses using salient morphologic features and results from ancillary studies. Fine-needle aspiration is an accurate method for the diagnosis of renal masses. A practical diagnostic algorithm, based on salient morphologic and ancillary findings, is presented.

Eosinophilic Solid and Cystic (ESC) Renal Cell Carcinomas Harbor TSC Mutations: Molecular Analysis Supports an Expanding Clinicopathologic Spectrum

Eosinophilic solid and cystic (ESC) renal cell carcinoma (RCC) has recently been described as a potentially new subtype of RCC based upon morphologic and immunohistochemical features. These neoplasms typically demonstrate solid and cystic architecture, and the neoplastic cells contain voluminous eosinophilic cytoplasm with granular cytoplasmic stippling. There is frequently focal immunoreactivity for cytokeratin 20. Although the initial cases all occurred in adult females and had benign outcome, we recently expanded the proposed spectrum of this neoplasm to include pediatric cases, multifocal neoplasms, and a case with hematogenous metastasis. ESC has been postulated to be analogous to a subtype of RCC consistently identified in tuberous sclerosis complex patients, and while previous work has demonstrated loss of heterozygosity at the TSC1 locus and copy number gains at TSC2 in ESC RCC, these genes have not been sequenced in ESC RCC. Using capture-based and amplicon-based next-generation sequencing, we now demonstrate the consistent presence of either TSC1 or TSC2 gene mutations in pediatric ESC RCC (8/9 cases) and adult ESC RCC (6/6 cases). These included a metastatic ESC RCC which had a complete response to mTOR targeted therapy. We also found these mutations in some neoplasms with variant morphology and thus potentially expand the spectrum of ESC RCC. These include one of our adult cases which demonstrated dominant "type 2" papillary RCC morphology and 2 of 3 previously unclassified pediatric RCC with features of ESC RCC minus granular cytoplasmic stippling. We also demonstrate TSC mutations in a case of so-called "oncocytoid RCC after neuroblastoma" with identical morphology and immunoprofile, providing a molecular link between the latter and ESC RCC. In summary, ESC RCC consistently harbors actionable TSC1 or TSC2 mutations, which are infrequently seen in established subtypes of RCC. These findings support TSC1/2 mutation as a molecular marker of ESC RCC, and suggest expansion of the clinicopathologic spectrum to include neoplasms with papillary architecture, occasional cases lacking well-developed granular cytoplasmic stippling, and a subset of RCC with oncocytic features in patients who have survived neuroblastoma.

Somatic Bi-allelic Loss of TSC Genes in Eosinophilic Solid and Cystic Renal Cell Carcinoma

Renal cell carcinomas (RCC) with overlapping histomorphologic features poses diagnostic challenges. This is exemplified in RCCs with eosinophilic cytoplasm that include eosinophilic solid and cystic RCC (ESC RCC), RCCs in germline aberrations of tuberous sclerosis complex (TSC) genes mutated (TSC RCC) individuals, and other RCC subtypes. We used next-generation sequencing (NGS) technology to molecularly profile seven ESC RCC tumors. Mutational and copy number analysis of NGS data revealed mutually exclusively somatic bi-allelic loss of TSC1 or TSC2 genes-both negative regulators of the mammalian target of rapamycin (mTOR) pathway in 85% (6/7) of evaluated cases. Thus, lack of germline TSC aberration in matched non-neoplastic renal parenchyma distinguishes ESC RCC from TSC RCC. Immunohistochemistry data shows mTOR pathway activation in all tumors, thus supporting a pathognomonic role for TSC aberrations in ESC RCC. Our study clarifies the molecular identity of ESC RCC, provides basis for the revision of current RCC classification, and may guide future therapeutic strategies.

PATIENT SUMMARY

Molecular characterization of eosinophilic solid and cystic renal cell carcinomas (ESC RCC) revealed recurrent and mutually exclusive somatic homozygous loss of tuberous sclerosis complex family genes. This observation provides greater insight into the unique biology of this novel type of tumor and potentially expands the therapeutic options for ESC RCC patients.

Molecular Characterization and Putative Pathogenic Pathways of Tuberous Sclerosis Complex-Associated Renal Cell Carcinoma

Tuberous sclerosis complex–associated renal cell carcinoma (TSC-RCC) has distinct clinical and histopathologic features and is considered a specific subtype of RCC. The genetic alterations of TSC1 or TSC2 are responsible for the development of TSC. In this study, we assessed the mTOR pathway activation and aimed to evaluate molecular characteristics and pathogenic pathways of TSC-RCC. Two cases of TSC-RCC, one from a 31-year-old female and the other from an 8-year-old male, were assessed. The mTOR pathway activation was determined by immunohistochemistry. The mutational spectrum of both TSC-RCCs was evaluated by whole exome sequencing (WES), and pathogenic pathways were analyzed. Differentially expressed genes were analyzed by NanoString Technologies nCounter platform. The mTOR pathway activation and the germline mutations of TSC2 were identified in both TSC-RCC cases. The WES revealed several cancer gene alterations. In Case 1, genetic alterations of CHD8, CRISPLD1, EPB41L4A, GNA11, NOTCH3, PBRM1, PTPRU, RGS12, SETBP1, SMARCA4, STMN1, and ZNRF3 were identified. In Case 2, genetic alterations of IWS1 and TSC2 were identified. Further, putative pathogenic pathways included chromatin remodeling, G protein–coupled receptor, Notch signaling, Wnt/β-catenin, PP2A and the microtubule dynamics pathway in Case 1, and mRNA processing and the PI3K/AKT/mTOR pathway in Case 2. Additionally, the ALK and CRLF2 mRNA expression was upregulated and CDH1, MAP3K1, RUNX1, SETBP1, and TSC1 mRNA expression was downregulated in both TSC-RCCs. We present mTOR pathway activation and molecular characteristics with pathogenic pathways in TSC-RCCs, which will advance our understanding of the pathogenesis of TSC-RCC.

Eosinophilic solid and cystic renal cell carcinoma mimicking epithelioid angiomyolipoma: series of 4 primary tumors and 2 metastases

Eosinophilic solid and cystic renal cell carcinoma (ESC-RCC) is a novel entity of rare tumors with rather unique morphology and immunohistochemical profile. Until recently these tumors were characterized by indolent behavior. Herein, we describe a series of six primary and metastatic ESC-RCCs morphologically and immunophenotypically mimicking epithelioid angiomyolipoma (eAML). Retrospective review of unclassified RCCs with oncocytic phenotype yielded several candidate cases, 4 of which fulfilled diagnostic criteria after additional work-up. Three female patients and one male (median age 46) presented with unifocal tumors ranging from 1.5 cm to 20.5 cm (median 5 cm). On follow-up (median 32 months), 2 younger patients had no signs of tumor recurrence, but older patients presented with advanced disease. A 50 year-old female developed numerous bone metastases and tumor progression despite aggressive treatment. Two of these metastases were analyzed showing morphology and immunoprofile similar to the primary tumor. 50 year-old male had locally aggressive tumor invading adrenal gland and retroperitoneum. All cases exhibited ESC-like architecture of solid sheets, tight nests and variably sized cysts with hobnailed lining, as well as foci of diffuse growth with poorly cohesive brightly eosinophilic cells. Characteristic cytoplasmic stippling and coarse granularity was present in all cases including compact cytoplasmic "Leishmaniasis-like" globules. Due to high suspicion of eAML, immunostaining panels included melanocytic markers, cytokeratins and RCC-specific markers. All ESC-RCC were positive for CK20 and melanocytic markers Melan-A, Cathepsin-K or HMB45, as well as PAX8, whereas EMA, pan-cytokeratin, CK7, CKIT, CD10, CAIX were negative. Comparison with 5 eAML cases including 2 malignant tumors showed similar morphology and immune reactivity except for more frequent expression of HMB45 and lack of PAX8 positivity. In conclusion, we report 2 cases of aggressive ESC-RCC course including widespread bone metastases in addition to 2 typical indolent tumors. ESC-RCC and eAML could present with overlapping morphology and immunophenotype causing diagnostic difficulty and expanding our understanding of these rare tumors.

Re-evaluation of 33 'unclassified' eosinophilic renal cell carcinomas in young patients

AIMS

We sought to determine if some unclassified renal cell carcinomas (RCCs) in children and young adults that are characterised by predominantly eosinophilic cytoplasm are related to the recently described succinate dehydrogenase (SDH)-deficient RCC, fumarate hydratase (FH)-deficient RCC or eosinophilic solid and cystic (ESC) RCC.

METHODS AND RESULTS

We reviewed 33 unclassified RCCs with predominantly eosinophilic cytoplasm in patients aged 35 years or younger. Immunohistochemistry (IHC) for SDHB, FH and CK20 (a marker of ESC) was performed in all cases. IHC for 2-succinocysteine (2SC) was performed on RCC with loss of FH labelling. Four RCC (12%) (median age 18 years) demonstrated loss of FH labelling as well as aberrant 2SC labelling, and were thus classified as FH-deficient RCCs. Importantly, none of these cases demonstrated the characteristic macronucleoli typical of FH-deficient RCC. Eight RCC (24%) (median age 20.5 years) demonstrated loss of SDHB and were reclassified as SDH-deficient RCCs. Importantly, only four of eight SDH-deficient RCC demonstrated the characteristic cytoplasmic vacuoles and inclusions of typical SDH-deficient RCC. Ten RCC (30%) (median age 27 years) were reclassified as ESC RCCs. Four of 10 ESC RCC were multifocal (one bilateral), four of 10 ESC RCC occurred in males and one patient presented with liver and lung metastases, all not described previously in ESC. Eleven RCC (33%) remained unclassified.

CONCLUSIONS

Pathologists should have a low threshold for performing FH, SDHB and CK20 IHC when confronted with unclassified eosinophilic RCC or 'oncocytoma' in young patients.

Eosinophilic Solid and Cystic Renal Cell Carcinoma (ESC RCC): Further Morphologic and Molecular Characterization of ESC RCC as a Distinct Entity

Eosinophilic solid and cystic renal cell carcinoma (ESC RCC) has been recently described as a unique and indolent renal neoplasm, found in female patients with and without tuberous sclerosis complex. Although ESC RCC has a distinct morphology and frequent CK20 reactivity, its molecular karyotype has been previously studied only in few cases. We identified 19 ESC RCC from multiple institutions; all patients were female individuals without clinical features of tuberous sclerosis complex. Molecular karyotyping was performed in 13 cases (12 with informative result). The median age was 55 years (range: 32 to 79 y). The tumors were yellow-gray with a median size of 31 mm (range: 12 to 135 mm) and showed solid and cystic gross appearance. All tumors demonstrated typical microscopic features with solid areas admixed with variably sized macrocysts and microcysts. The cells showed eosinophilic cytoplasm with granular cytoplasmic stippling and round-to-oval nuclei. CK20 was positive in 14/19 (74%) cases. Stage pT1 was found in 17/19 (89%) patients (pT1a in 12, pT1b in 5); 1 patient each had pT2a and pT3a. A total of 15/16 patients with available follow-up were alive and without evidence of disease progression, after 1 to 169 months (median: 44 mo; mean: 49.6 mo); 3 died of other causes. The most common copy number gains were 16p13.3-16q23.1 (33% to 67%), 7p21.2-7q36.2 (42% to 50%), 13q14.2 (33%), and 19p12 (33%). The most common copy number losses included Xp11.21 (42%) and 22q11.23 (33%). Loss of heterozygosity was most frequently found at 16p11.2-11.1 (75%), Xq11.1-13.1 (75%), Xq13.1-21.1 (33%), 11p11.2-11.11 (33%), 9q21.1-22.2 (33%), and 9q33.1 (33%). ESC RCC demonstrates common molecular karyotype alterations, which further support its distinct nature.

Renal Cell Carcinoma Occurring in Patients With Prior Neuroblastoma: A Heterogenous Group of Neoplasms

Renal cell carcinoma (RCC) associated with neuroblastoma (NB) was included as a distinct entity in the 2004 World Health Organization classification of kidney tumors. A spectrum of RCC subtypes has been reported in NB survivors. We herein describe a series of 8 RCCs diagnosed in 7 patients with a history of NB. Microscopic evaluation, immunohistochemical staining for PAX8, cathepsin K, and succinate dehydrogenase subunit B (SDHB), and fluorescence in situ hybridization (FISH) for TFE3 and TFEB were performed. Four distinct morphologic subtypes were identified: 3 tumors were characterized by cells with abundant oncocytoid cytoplasm and irregular nuclei; 3 showed features of microphthalmia transcription factor family translocation RCC (MiTF-RCC); 1 had features of hybrid oncocytic-chromophobe tumor; 1 had papillary RCC histology. All RCCs expressed PAX8 and retained SDHB expression. Cathepsin K was positive in 2 MiTF-RCCs, 1 was TFEB FISH positive, and the other was indeterminate. Cathepsin K was negative in a third MiTF-RCC with TFE3 rearrangement. TFE3 FISH was negative in 4 and insufficient in 1 of the other 5 RCCs. While a subset of RCCs associated with NB is characterized by cells with prominent oncocytoid cytoplasm, other RCC subtypes also occur in post-NB patients. Renal neoplasms occurring in patients with a history of NB do not represent a single entity but a heterogenous group of RCCs. SDHB mutations do not explain the subset of nontranslocation RCCs with oncocytoid features; therefore, further studies are needed to clarify whether they may represent a distinct entity with unique molecular abnormalities or may belong to other emerging RCC subtypes.

[Succinate dehydrogenase (SDH)-deficient renal cell carcinoma]

Succinate dehydrogenase (SDH) represents a type II mitochondrial complex related to the respiratory chain and Krebs cycle. The complex is composed of four major subunits, SDHA, SDHB, SDHC and SDHD. The oncogenic role of this enzyme complex has only recently been recognized and the complex is currently considered an important oncogenic signaling pathway with tumor suppressor properties. In addition to the familial paraganglioma syndromes (types 1-5) as prototypical SDH-related diseases, many other tumors have been defined as SDH-deficient, in particular a subset of gastrointestinal stromal tumors (GIST), rare hypophyseal adenomas, a subset of pancreatic neuroendocrine neoplasms (recently added) and a variety of other tumor entities, the latter mainly described as rare case reports. As a central core subunit responsible for the integrity of the SDH complex, the expression of SDHB is lost in all SDH-deficient neoplasms irrespective of the specific SDH subunit affected by a genetic mutation in addition to concurrent loss of the subunit specifically affected by genetic alteration. Accordingly, all SDH-deficient neoplasms are by definition SDHB-deficient. The SDH-deficient renal cell carcinoma (RCC) has only recently been well-characterized and it is included as a specific subtype of RCC in the new World Health Organization (WHO) classification published in 2016. In this review, the major clinicopathological, immunohistochemical and genetic features of this rare disease entity are presented and discussed in the context of the broad differential diagnosis.

[Hereditary renal tumors: More common than expected?]

Renal cell carcinomas are associated with hereditary tumor syndromes in approximately 5 % of cases. In patients with a hereditary predisposition, tumors show an earlier age of onset, often with a multicentric and bilateral manifestation. While some patients with renal cell carcinoma can be classified into well-characterized kidney cancer syndromes others have a genetic background which is still poorly understood. Most of the specific tumor syndromes are associated with a histopathologically distinct renal cell tumor phenotype. The recognition of patients with hereditary renal cell carcinoma and the identification of individual family members with a higher risk of development of renal tumors is important for early tumor detection and treatment. This manuscript reviews the clinical pathological and molecular findings of hereditary renal cell carcinoma syndromes.