Tubulocystic carcinoma of the kidney: clinicopathologic analysis of 31 cases of a distinctive rare subtype of renal cell carcinoma. Am J Surg Pathol. 2009;33:384-392. [PMID: 19011562 DOI: 10.1097/pas.0b013e3181872d3f]

Cystic Features in Renal Epithelial Neoplasms and Their Increasing Clinical and Pathologic Significance

Most cystic renal tumors after resection (Boniak IIF to IV cysts) have an indolent course despite the significantly higher proportion of malignant [ie, renal cell carcinoma (RCC)] diagnosis. Most cystic renal tumors have clear cell histology that include cystic clear cell RCC and multilocular cystic renal neoplasm of low malignant potential (MCNLMP). There is growing evidence to suggest that MCNLMP, cystic clear cell RCC, and noncystic clear cell RCC form a cystic-to-solid biological spectrum with MCNLMP representing the most indolent form and with cystic clear cell RCC behaving better than noncystic (solid) clear cell RCC. Extensively (>75%) cystic clear cell RCC also has an excellent outcome similar to MCNLMP stressing the need to reevaluate the histologic criteria that separate these 2 cystic clear cell tumors. Other tumors with clear cells that can be extensively cystic such as the recently reclassified noncancerous clear cell papillary renal tumor and the newly described MED15::TFE3 RCC also have indolent course and may mimic MCNLMP. Cystic features occur also in renal tumors with nonclear cell histology including tumors capable of metastasis such as acquired cystic disease-associated, tubulocystic, fumarate hydratase-deficient, and eosinophilic solid and cystic RCCs. Cystic imaging presentation of some renal tumors such as papillary RCC can be attributed in part to pseudocystic necrosis and hemorrhage. It is important to know that tubulocystic RCC may have a lower Bosniak class presentation that overlaps with benign renal cysts (Bosniak I to IIF) that are managed conservatively. This review highlights the cystic renal tumors with clear cell and nonclear cell morphologies including some novel RCC subtypes that may have cystic features. The presence of cystic features and their extent may aid in the classification and prognostication of renal neoplasms underscoring its increasing importance in the pathologic diagnosis and reporting of renal neoplasia.

Recent Advances in Pathology of Intrahepatic Cholangiocarcinoma

Intrahepatic cholangiocarcinoma (ICCA) is a malignant epithelial neoplasm characterized by biliary differentiation within the liver. ICCA is molecularly heterogeneous and exhibits a broad spectrum of histopathological features. It is a highly aggressive carcinoma with high mortality and poor survival rates. ICCAs are classified into two main subtypes: the small-duct type and large-duct types. These two tumor types have different cell origins and clinicopathological features. ICCAs are characterized by numerous molecular alterations, including mutations in KRAS, TP53, IDH1/2, ARID1A, BAP1, BRAF, SAMD4, and EGFR, and FGFR2 fusion. Two main molecular subtypes-inflammation and proliferation-have been proposed. Recent advances in high-throughput assays using next-generation sequencing have improved our understanding of ICCA pathogenesis and molecular genetics. The diagnosis of ICCA poses a significant challenge for pathologists because of its varied morphologies and phenotypes. Accurate diagnosis of ICCA is essential for effective patient management and prognostic determination. This article provides an updated overview of ICCA pathology, focusing particularly on molecular features, histological subtypes, and diagnostic approaches.

Papillary Renal Cell Carcinoma: A Review of Prospective Clinical Trials

OPINION STATEMENT

PRCC is a unique histologic entity compared to other forms of renal cell carcinoma, harboring distinct molecular drivers. The WHO 2022 classification is further emphasizing the molecular biology by making molecular classifications of PRCC subclassifications and discontinuing the morphologic type 1 and type 2 classification system. We agree with this functional classification system and encourage all future clinical trials to only include patients with similar diagnosis instead of conducting basket trials (including all nccRCC together) which limits the scientific value of those conclusions. Based on recent disease-specific clinical trial (S1500, PAPMET), the current standard of care for patients with treatment naïve PRCC is cabozantinib. Prospective clinical trials clearly establish that immune checkpoint inhibitor therapy has meaningful activity in PRCC. The data to date include only single-arm clinical trials of combination immune therapy. Despite the positive and encouraging results, we need validation through randomized studies because of the overestimation of effect size seen in single-arm trials. These randomized trials are currently underway and enrolling. We strongly encourage all physicians to support these studies and enroll patients with PRCC to these trials in order to continue improving the standard of care.

Radical versus partial nephrectomy for T1 non-clear cell renal cell carcinoma

INTRODUCTION

Nephron-sparing surgery is the recommended surgical management of T1 renal cell carcinoma (RCC). However, non-clear cell RCC (nccRCC) is heterogeneous and included many histological types. Therefore, the present study was performed to compare radical nephrectomy (RN) versus partial nephrectomy (PN) in nccRCC.

MATERIALS AND METHODS

Within the Surveillance, Epidemiology, and End Results registry (2000-2019), the patients with nccRCC were identified. Kaplan-Meier survival curve and the log-rank test were conducted. Univariate analysis and multivariate Cox regression analysis were performed to explore the prognostic factors.

RESULTS

A total of 7575 patients with nccRCC were included, of which papillary RCC (n = 5219) is the major histology. Kaplan-Meier plots and log-rank tests showed that nccRCC patients who underwent RN had significantly worse overall survival (OS) and cancer-specific survival (CSS) than those who received PN (all P < 0.05). Multivariate analysis also revealed that RN was significantly associated with poor OS and CSS in nccRCC patients. Stratified by histological types, the multivariate analysis also revealed that RN was significantly associated with poor OS in papillary and chromophobe (all P < 0.05). Besides, the multivariable analysis indicated that RN was associated with poor CSS in papillary RCC (P < 0.05). For other histology, the patients who received RN had a comparable survival to those who received PN.

CONCLUSION

For patients with T1 nccRCC, our findings revealed that PN was not inferior to RN in OS and CSS. PN may be also the preferred option for T1 nccRCC, but more prospective studies are required to validate this finding.

Cystic Renal Masses: Old and New Paradigms

Cystic renal masses describe a spectrum of lesions with benign and/or malignant features. Cystic renal masses are most often identified incidentally with the Bosniak classification system stratifying their malignant potential. Solid enhancing components most often represent clear cell renal cell carcinoma yet display an indolent natural history relative to pure solid renal masses. This has led to an increased adoption of active surveillance as a management strategy in those who are poor surgical candidates. This article provides a contemporary overview of historical and emerging clinical paradigms in the diagnosis and management of this distinct clinical entity.

Durable Response to Pazopanib in a Patient with Fumarate Hydratase-Mutant Tubulocystic Renal Cell Carcinoma

Tubulocystic carcinoma of the kidney (TC-RCC) is a rare renal tumor and has been recently included as a distinct entity in WHO classification of renal neoplasms. We report the case of a patient with metastatic tubulocystic RCC whose disease progressed through standard of care treatment for nonclear RCC. However, genetic analysis revealed a germline pathogenic variant of fumarate hydratase (FH) gene, and the patient had a sustained and durable response to pazopanib.

Updates in Grading of Renal Cell Carcinomas Beyond Clear Cell Renal Cell Carcinoma and Papillary Renal Cell Carcinoma

The World Health Organization (WHO) recommends grading of clear cell renal cell carcinoma (RCC) and papillary RCC using the WHO/International Society of Urological Pathology (ISUP) grade, which is primarily based on nuclear features. As the spectrum of RCC continues to evolve, with more recently described subtypes in the past decade, literature evidence on grading these subtypes is limited or not available for some tumor types. Herein, we outline a pragmatic approach to the topic of grading RCC, dividing the contemporarily described RCC subtypes into 7 categories based on the potential clinical applicability of grading as a useful prognostic parameter: (1) RCC subtypes that are reasonably validated and recommended for WHO/ISUP grading; (2) RCC subtypes where WHO/ISUP is not applicable; (3) RCC subtypes where WHO/ISUP grading is potentially clinically useful; (4) inherently aggressive RCC subtypes where histologic classification itself confers an aggressive biologic potential; (5) renal epithelial tumors where WHO/ISUP grading provides potentially misleading prognostic implication; (6) renal epithelial neoplasms where low WHO/ISUP grade features are a prerequisite for accurate histologic classification; and (7) renal epithelial neoplasms with no or limited data on grading or incomplete understanding of the biologic potential. Our aim in outlining this approach is 2-fold: (a) identify the gaps in understanding and application of grading in RCC subtypes so that researchers in the field may perform additional studies on the basis of which the important pathologic function of assignment of grade may be recommended to be performed as a meaningful exercise across a wider spectrum of RCC; and (b) to provide guidance in the interim to surgical pathologists in terms of providing clinically useful grading information in RCC based on currently available clinicopathologic information.

Tubulocystic Renal Cell Carcinoma Is Not an Indolent Tumor: A Case Report of Recurrences in the Retroperitoneum and Contralateral Kidney

Tubulocystic renal cell carcinoma (RCC) is a rare subtype of RCC that was recently included in the 2016 World Health Organization classification of tumors of the kidney. Most of these tumors exhibit indolent behavior with low metastatic potential. However, here we report a case of recurrent tubulocystic RCC with aggressive features in the retroperitoneum and contralateral kidney treated with targeted agents and radiofrequency ablation.

A unique presentation of a rare renal cancer: Appearance of bone metaplasia in tubulocystic renal cell carcinoma

Tubulocystic renal cell carcinoma is a rare cancer that was not defined as a distinct entity until the early 2000s. Due to the recency of its classification, it remains poorly understood and leaves much room for future research. This report looks at a unique case of this rare subtype of renal cancer. This specific case is unique due to both the demographics of the affected patient and the finding of bone metaplasia within the tumor. We believe this is the first ever reported incidence of this phenomenon.

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.

A 25 year perspective on advances in the pathologic assessment and diagnosis of urologic cancers

Over the past 25 years, diagnostic categories in genitourinary pathology have changed dramatically. Prostate cancer reporting incorporated numerous new variant categories, recognized the importance of intraductal carcinoma, and introduced the concept of Grade Groups. Pathologic diagnosis of bladder cancer not only added new variant categories, but also modified the grading of non-invasive urothelial neoplasms and refined staging definitions. Kidney cancer classification expanded from a handful of diagnostic categories to a broad array of additional cancer types defined by unique immunohistochemical and molecular findings. Segregation of penile carcinoma by human papillomavirus status more accurately reflected pathogenesis and helped improve prediction of cancer behavior. Testicular pathology research advanced understanding of germ cell tumor subtypes and their impact on patient outcomes. Finally, adrenal gland pathology has evolved to incorporate a broader recognition of morphological variation and risk factors associated with tumor progression. Taken together, changes in pathology over the past quarter century have revolutionized our approach to genitourinary cancers. This review seeks to highlight some of the many significant changes in genitourinary pathology that have occurred during the past 25 years and emphasize impacts on clinical outcomes or therapy, as relevant.

Tubulocystic renal cell carcinoma: Two-case report and literature review

Tubulocystic renal cell carcinoma is a rare neoplasm of kidney with low metastatic tendency. There has only been a relatively small collection of literature dedicated to this subtype. Here we present two cases diagnosed in our center with detailed clinical information. Along with literature review, we aim to paint a comprehensive profile of TC-RCC. Hematuria and asthenia could be the chief complaints although most patients are asymptomatic. This lesion has a signature multilocular cystic form on radiology and enhancement of septa should reveal malignancy. Histologically, the cysts are lined by a single layer of flattened, cuboidal/columnar, and hobnail epithelium with enlarged nuclei and intermediate to large nucleoli. PAX8 and AMACR are most commonly positive while CD10 or CK7 could be focally stained in some cases. Overall, the diagnosis of TC-RCC should be based on comprehensive clinical and molecular results because early determination of the lesion could prelude a timely intervention and favorable prognosis.

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.

Rarest of the Rare Metastatic Tubulocystic Carcinoma of Kidney

Tubulocystic carcinoma of the kidney is a rare neoplasm with <100 case reports. Patients are usually asymptomatic and have a relatively indolent disease course occurring predominantly in males. These tumors rarely metastasize. It was previously considered to have some similarities to various other renal cancers, although this tumor has distinct macroscopic, microscopic, and immunohistochemical features. It is now a well-established entity in renal neoplastic pathology. Herein we present a case of metastatic tubulocystic carcinoma presenting with bony metastasis.

Bellini duct carcinoma revealed by cutaneous metastasis: A case report

•

Cutaneous metastasis of renal cell carcinoma is rare.

•

Bellini carcinoma is a very rare type of carcinoma of renal cell origin with a very poor prognosis.

•

Multiple skin metastases from an asymptomatic Bellini's carcinoma are exceptional.

Introduction

Cutaneous metastasis of renal cell carcinoma is rare and the majority of these metastases are asynchronous. The scalp and face are the major sites of metastases, followed by the chest and abdomen. However, the entire body surface can be affected. When diagnosed, patients are multi-metastatic in 50–80% of cases during follow-up post nephrectomy.

Case presentation

We report here a patient who consulted a dermatologist for multiple skin nodules that appeared 3 months prior. A skin biopsy of a nodule was performed and the pathological examination and immunohistochemistry profile confirmed a metastasis of Bellini Carcinoma, which is a renal cell carcinoma of the collecting duct. A thoraco-abdomino-pelvic scan showed a left renal tumor locally advanced with lung and liver metastases. Chemotherapy was indicated and the patient died four months after diagnosis.

Discussion

Bellini carcinoma is a very rare type of carcinoma of renal cell origin with a very poor prognosis as it is diagnosed already at a metastatic state in the vast majority of cases. After analysis of the data from the literature, our case is the second reported case of a Bellini carcinoma revealed by cutaneous metastases. The peculiarity of our observation is metastases occurred on all four limbs and at the trunk level, and the asymptomatic characteristic of Bellini's carcinoma, which is a rare situation.

Conclusion

The originality of this observation is based on the mode of presentation of a rare renal tumor by an even rarer metastasis of the skin.

Renal Cell Tumors: Molecular Findings Reshaping Clinico-pathological Practice

Over the past 20 years, the number of subtypes of renal epithelial cell neoplasia has grown. This growth has resulted from detailed histological and immunohistochemical characterization of these tumors and their correlation with clinical outcomes. Distinctive molecular phenotypes have validated the unique nature of many of these tumors. This growth of unique renal neoplasms has continued after the 2016 World Health Organization (WHO) Classification of Tumours. A consequence is that both the pathologists who diagnose the tumors and the clinicians who care for these patients are confronted with a bewildering array of renal cell carcinoma variants. Many of these variants have important clinical features, i.e. familial or syndromic associations, genomics alterations that can be targeted with systemic therapy, and benignancy of tumors previously classified as carcinomas. Our goal in the review is to provide a practical guide to help recognize these variants, based on small and distinct sets of histological features and limited numbers of immunohistochemical stains, supplemented, as necessary, with molecular features.

Genetic Alterations in Renal Cancers: Identification of The Mechanisms Underlying Cancer Initiation and Progression and of Therapeutic Targets

Renal cell cancer (RCC) involves three most recurrent sporadic types: clear-cell RCC (70-75%, CCRCC), papillary RCCC (10-15%, PRCC), and chromophobe RCC (5%, CHRCC). Hereditary cases account for about 5% of all cases of RCC and are caused by germline pathogenic variants. Herein, we review how a better understanding of the molecular biology of RCCs has driven the inception of new diagnostic and therapeutic approaches. Genomic research has identified relevant genetic alterations associated with each RCC subtype. Molecular studies have clearly shown that CCRCC is universally initiated by Von Hippel Lindau (VHL) gene dysregulation, followed by different types of additional genetic events involving epigenetic regulatory genes, dictating disease progression, aggressiveness, and differential response to treatments. The understanding of the molecular mechanisms that underlie the development and progression of RCC has considerably expanded treatment options; genomic data might guide treatment options by enabling patients to be matched with therapeutics that specifically target the genetic alterations present in their tumors. These new targeted treatments have led to a moderate improvement of the survival of metastatic RCC patients. Ongoing studies based on the combination of immunotherapeutic agents (immune check inhibitors) with VEGF inhibitors are expected to further improve the survival of these patients.

Updates in Histologic Grading of Urologic Neoplasms

CONTEXT.—

Tumor histology offers a composite view of the genetic, epigenetic, proteomic, and microenvironmental determinants of tumor biology. As a marker of tumor histology, histologic grading has persisted as a highly relevant factor in risk stratification and management of urologic neoplasms (ie, renal cell carcinoma, prostatic adenocarcinoma, and urothelial carcinoma). Ongoing research and consensus meetings have attempted to improve the accuracy, consistency, and biologic relevance of histologic grading, as well as provide guidance for many challenging scenarios.

OBJECTIVE.—

To review the most recent updates to the grading system of urologic neoplasms, including those in the 2016 4th edition of the World Health Organization (WHO) Bluebook, with emphasis on issues encountered in routine practice.

DATA SOURCES.—

Peer-reviewed publications and the 4th edition of the WHO Bluebook on the pathology and genetics of the urinary system and male genital organs.

CONCLUSIONS.—

This article summarizes the recently updated grading schemes for renal cell carcinoma, prostate adenocarcinomas, and bladder neoplasms of the genitourinary tract.

Report From the International Society of Urological Pathology (ISUP) Consultation Conference on Molecular Pathology of Urogenital Cancers: III: Molecular Pathology of Kidney Cancer

Renal cell carcinoma (RCC) subtypes are increasingly being discerned via their molecular underpinnings. Frequently this can be correlated to histologic and immunohistochemical surrogates, such that only simple targeted molecular assays, or none at all, are needed for diagnostic confirmation. In clear cell RCC, VHL mutation and 3p loss are well known; however, other genes with emerging important roles include SETD2, BAP1, and PBRM1, among others. Papillary RCC type 2 is now known to include likely several different molecular entities, such as fumarate hydratase (FH) deficient RCC. In MIT family translocation RCC, an increasing number of gene fusions are now described. Some TFE3 fusion partners, such as NONO, GRIPAP1, RBMX, and RBM10 may show a deceptive fluorescence in situ hybridization result due to the proximity of the genes on the same chromosome. FH and succinate dehydrogenase deficient RCC have implications for patient counseling due to heritable syndromes and the aggressiveness of FH-deficient RCC. Immunohistochemistry is increasingly available and helpful for recognizing both. Emerging tumor types with strong evidence for distinct diagnostic entities include eosinophilic solid and cystic RCC and TFEB/VEGFA/6p21 amplified RCC. Other emerging entities that are less clearly understood include TCEB1 mutated RCC, RCC with ALK rearrangement, renal neoplasms with mutations of TSC2 or MTOR, and RCC with fibromuscular stroma. In metastatic RCC, the role of molecular studies is not entirely defined at present, although there may be an increasing role for genomic analysis related to specific therapy pathways, such as for tyrosine kinase or MTOR inhibitors.

Tubulocystic Renal Cell Carcinoma in Young Adult

Tubulocystic renal cell carcinoma is a uncommon neoplasm with unique pathological features and indolent clinical behaviour. We are reporting a case of tubulocystic renal cell carcinoma in young adult managed by partial nephrectomy.

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.

Current Concepts of Non-Coding RNAs in the Pathogenesis of Non-Clear Cell Renal Cell Carcinoma

Renal cell carcinoma (RCC) is a relatively rare malignancy of the urinary tract system. RCC is a heterogenous disease in terms of underlying histology and its associated underlying pathobiology, prognosis and treatment schedule. The most prevalent histological RCC subtype is clear-cell renal cell carcinoma (ccRCC), accounting for about 70-80% of all RCCs. Though the pathobiology and treatment schedule for ccRCC are well-established, non-ccRCC subtypes account for 20%-30% of RCC altogether, and their underlying molecular biology and treatment options are poorly defined. The class of non-coding RNAs-molecules that are generally not translated into proteins-are new cancer drivers and suppressors in all types of cancer. Of these, small non-coding microRNAs (miRNAs) contribute to carcinogenesis by regulating posttranscriptional gene silencing. Additionally, a growing body of evidence supports the role of long non-coding RNAs (lncRNAs) in cancer development and progression. Most studies on non-coding RNAs in RCC focus on clear-cell histology, and there is a relatively limited number of studies on non-ccRCC subtypes. The aim of this review is to give an overview of the current knowledge regarding the role of non-coding RNAs (including short and long non-coding RNAs) in non-ccRCC and to highlight possible implications as diagnostic, prognostic and predictive biomarkers.

A simple cyst is not always simply a cyst: A case of cystic recurrence after nephrectomy for tubulocystic renal cell carcinoma and literature review

Tubulocystic renal cell carcinoma is a rare subtype of renal tumor according to the 2016 World Health Organization, and less than 100 cases have been documented up to date in literature. The imaging features are not well known and to the best of our knowledge, there is not a radiology description of recurrence from tubulocystic renal cell carcinoma in the literature. We describe the case of a 70-year-old man with unusual cystic lesions in the left hypochondrium 11 years after a nephrectomy for tubulocystic renal cell carcinoma on the same side, and we report a review of the clinical characteristics of metastatic tubulocystic renal cell carcinoma.

Unusual Suspect: A Case Report of Tubulocystic Renal Cell Carcinoma with Features of Cystic Renal Oncocytoma

Tubulocystic renal cell carcinoma is an uncommon subtype of renal cell carcinoma that was only recently acknowledged by the World Health Organization. There is a relatively small collection of literature dedicated to the features and clinical course of this lesion. Despite its rarity, this diagnosis should remain in the differential for all cystic renal masses. We present a case report of tubulocystic renal cell carcinoma (TC-RCC) with remarkable similarity to cystic renal oncocytoma, highlighting the diagnostic challenges associated with this unusual renal malignancy.

Current Challenges in Diagnosis and Assessment of the Response of Locally Advanced and Metastatic Renal Cell Carcinoma

Locally advanced and metastatic renal cell carcinoma (RCC) present a specific set of challenges to the radiologist. The detection of metastatic disease is confounded by the ability of RCC to metastasize to virtually any part of the human body long after surgical resection of the primary tumor. This includes sites not commonly included in routine surveillance, which come to light after the patient becomes symptomatic. In the assessment of treatment response, the phenomenon of tumor heterogeneity, where clone selection through systemic therapy drives the growth of potentially more aggressive phenotypes, can result in oligoprogression despite overall disease control. Finally, advances in therapy have resulted in the development of immuno-oncologic agents that may result in changes that are not adequately evaluated with conventional size-based response criteria and may even be misinterpreted as progression. This article reviews the common challenges a radiologist may encounter in the evaluation of patients with locally advanced and metastatic RCC. ^©RSNA, 2019.

Tubulocystic renal cell carcinoma: a distinct clinicopathologic entity with a characteristic genomic profile

Tubulocystic renal cell carcinoma, a unique tumor, was recently included as a new entity in the World Health Organization classification of renal tumors. It has variably been reported to be related to other renal cell carcinomas, including papillary renal cell carcinoma, fumarate hydratase-deficient carcinoma, and others, likely because many such carcinomas may show variable amounts of tubulocystic architecture. The published data characterizing the molecular features of these tumors are inconsistent. We studied nine "pure" tubulocystic renal cell carcinomas, as defined by International Society of Urologic Pathologists (ISUP) and World Health Organization (WHO), by targeted next-generation sequencing, and fluorescence in situ hybridization for X and Y chromosomes, to investigate if these show any unique characteristics or any overlap with known mutational/molecular profiles or copy number alterations in other subtypes of renal cell carcinoma. All nine tubulocystic carcinomas demonstrated combined losses at chromosome 9 and gains at chromosome 17, as well as, loss of chromosome Y (in 5/5). None of the tumors showed mutational profiles characteristic of other renal neoplasms, including those seen in fumarate hydratase-deficient renal cell carcinoma. Recurrent mutations in chromatin-modifying genes, KMT2C and KDM5C, were detected in two of nine tumors. Thus, tubulocystic renal cell carcinoma, if defined strictly, at the clinical and pathologic level, demonstrates genomic features distinct from other subtypes of renal cell carcinoma. These findings support the contention that tubulocystic renal cell carcinoma should be diagnosed only using strict morphological criteria and only when presenting in a "pure" form; presence of variable papillary, poorly differentiated, or other architectural patterns most likely do not belong to the category of tubulocystic renal cell carcinoma.

The history of urologic pathology: an overview

This article begins with the testis and a legendary figure, Sir Astley Cooper, who wrote an early text on the organ. The early 20th century saw the first major development, the description of the seminoma by the French investigator Maurice Chevassu, but the pace of knowledge did not accelerate until after World War II with a major article from the Armed Forces Institute of Pathology (AFIP) by Nathan B. Friedman and Robert A. Moore, soon followed by the first series testis fascicle by Frank J. Dixon and Moore. Other noteworthy contributions were made by two masters of gonadal pathology, Gunnar Teilum and Robert E. Scully. In the 1970s, Niels E. Skakkebaek played a seminal role in elaborating in-situ neoplasia of the testis. The school of British testicular tumour authored, in the mid-1970s, under the editorship of Roger C. B. Pugh, one of the best texts on testicular pathology. Advances in more recent years have been largely spearheaded by Thomas M. Ulbright of the Indiana University School of Medicine. Observations on the prostate gland date back to Andreas Vesalius and William Cheselden, the latter appearing to have introduced the word for the gland. Note is made of contributions on the anatomy and histology of the gland by Oswald Lowsley, L. M. Franks, and John McNeal. Diagnosing carcinoma of the prostate was brought into the modern age in a landmark 1953 article by Robert S. Totten et al. In the 1960s, Donald F. Gleason introduced a grading system that is now in use worldwide. The topic of premalignant lesions has been well established only for approximately three decades, based initially on the work of Dr McNeal and David G. Bostwick. One of the first to write a book on the bladder was the remarkable British surgeon-pathologist Sir Henry Thompson. Workers at the AFIP, including Colonel James E. Ash and Fatallah K. Mostofi, wrote many outstanding articles on bladder pathology. The roles of other institutions, such as Johns Hopkins University, the Mayo Clinic, and St Peter's Hospital Institute of Urology, London, and those who worked there are noted. Knowledge of the pathology of the urachus dates largely back to the remarkable book on the topic in 1916 by the Hopkins investigator Thomas S. Cullen. Information on renal tumours dates largely to the work of Paul Grawitz, but awareness of the many variants of renal cell carcinoma in general was slow to evolve, and has only accelerated in recent years. The AFIP group of Dr Mostofi, ably assisted by Colonel Charles J. Davis and Isabell A. Sesterhenn, has contributed to knowledge of renal neoplasia with articles of note on oncocytoma, metanephric adenoma, and medullary carcinoma. In the mid-1980s, the German workers Wolfgang Thoenes and Stephan Störkel recognised the distinctive tumour known as chromophobe renal cell carcinoma. Work on renal tumours in the young owes much to J. Bruce Beckwith. The observational talents of numerous investigators have, in just over a century, advanced our knowledge of diseases of the urinary tract and testis remarkably.

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.

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.

Classification and Diagnosis of Cystic Renal Tumors: Role of MR Imaging Versus Contrast-Enhanced Ultrasound

Superior soft tissue and contrast resolution of MR imaging benefits sensitivity to kidney cyst features and classification, which may have an impact on patient management and outcomes. Contrast-enhanced ultrasound (CEUS) may have nearly similar sensitivity for detection of cyst features yet is dependent on patient body habitus and adequacy of visualization windows for the kidneys, which does not have the same impact on MR imaging results. Both MR imaging and CEUS may provide superior kidney cyst assessment compared with contrast-enhanced CT; however, further research is needed, particularly for the identification of role of CEUS.

Update on the biology and management of renal cell carcinoma

Renal cell cancer (RCC) (epithelial carcinoma of the kidney) represents 2%-4% of newly diagnosed adult tumors. Over the past 2 decades, RCC has been better characterized clinically and molecularly. It is a heterogeneous disease, with multiple subtypes, each with characteristic histology, genetics, molecular profiles, and biologic behavior. Tremendous heterogeneity has been identified with many distinct subtypes characterized. There are clinical questions to be addressed at every stage of this disease, and new targets being identified for therapeutic development. The unique characteristics of the clinical presentations of RCC have led to both questions and opportunities for improvement in management. Advances in targeted drug development and understanding of immunologic control of RCC are leading to a number of new clinical trials and regimens for advanced disease, with the goal of achieving long-term disease-free survival, as has been achieved in a proportion of such patients historically. RCC management is a promising area of ongoing clinical investigation.

Contemporary update on imaging of cystic renal masses with histopathological correlation and emphasis on patient management

This article presents an updated review of cystic renal mass imaging. Most cystic renal masses encountered incidentally are benign and can be diagnosed confidently on imaging and require no follow-up. Hyperattenuating masses discovered at unenhanced or single-phase enhanced computed tomography (CT) measuring between 20-70 HU are indeterminate and can be further investigated first by using ultrasound and, then with multi-phase CT or magnetic resonance imaging (MRI); as the majority represent haemorrhagic/proteinaceous cysts (HPCs). Dual-energy CT may improve differentiation between HPCs and masses by suppressing unwanted pseudo-enhancement observed with conventional CT. HPCs can be diagnosed confidently when measuring >70 HU at unenhanced CT or showing markedly increased signal on T1-weighted imaging. Although the Bosniak criteria remains the reference standard for diagnosis and classification of cystic renal masses, histopathological classification and current management has evolved: multilocular cystic renal cell carcinoma (RCC) has been reclassified as a cystic renal neoplasm of low malignant potential, few Bosniak 2F cystic masses progress radiologically during follow-up; RCC with predominantly cystic components are less aggressive than solid RCC; and Bosniak III cystic masses behave non-aggressively. These advances have led to an increase in non-radical management or surveillance of cystic renal masses including Bosniak 3 lesions. Tubulocystic RCC is a newly described entity with distinct imaging characteristics, resembling a pancreatic serous microcystadenoma. Other benign cystic masses including: mixed epithelial stromal tumours (MEST) are now considered in the spectrum of cystic nephroma and angiomyolipoma (AML) with epithelial cysts (AMLEC) resemble a fat-poor AML with cystic components.

The Probability of Aggressive Versus Indolent Histology Based on Renal Tumor Size: Implications for Surveillance and Treatment

BACKGROUND

While the probability of malignant versus benign histology based on renal tumor size has been described, this alone does not sufficiently inform decision-making in the modern era since indolent malignant tumors can be managed with active surveillance.

OBJECTIVE

To characterize the probability of aggressive versus indolent histology based on radiographic tumor size.

DESIGN, SETTING, AND PARTICIPANTS

We evaluated patients who underwent radical or partial nephrectomy at Mayo Clinic for a pT1-2, pNx/0, M0 solid renal tumor between 1990 and 2010. Pathology was reviewed by one genitourinary pathologist. High-grade clear-cell renal cell carcinoma (RCC), high-grade papillary RCC, collecting duct RCC, translocation-associated RCC, hereditary leiomyomatosis RCC, unclassified RCC, and malignant non-RCC tumors were all considered aggressive, as well as any tumors demonstrating coagulative necrosis (except low-grade papillary RCC) or sarcomatoid differentiation. The remaining benign and malignant tumors were considered indolent.

OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS

Cancer-specific survival (CSS) was estimated using the Kaplan-Meier method. Logistic regression models were used to estimate the probability of malignant and aggressive histology based on tumor size. Sex-stratified analyses were also performed.

RESULTS AND LIMITATIONS

Of the 2650 patients included, there were 1860 patients with indolent tumors (300 benign; 1560 malignant) and 790 with aggressive tumors. The 10-yr CSS was 96% for indolent malignant tumors and 81% for aggressive malignant tumors. The predicted percentages of any malignant histology as well as aggressive histology increased with tumor size. Specifically, 2cm, 3cm, and 4cm tumors have an estimated 84%, 87%, and 88% likelihood of malignancy, respectively, and an 18%, 24%, and 29% likelihood of aggressive histology, respectively. For any given tumor size, men had a greater chance of aggressive histology than women. Potential limitations of this observational surgical cohort include selection bias.

CONCLUSIONS

We present tumor size-based estimates of the probability of aggressive histology for renal masses. This information should be useful for initial patient counseling and management.

PATIENT SUMMARY

Active surveillance is an option for kidney masses, even if they are malignant. Beyond knowing whether the mass is benign or cancer, it is important to know whether or not it is an aggressive tumor. This study presents tumor size-specific and sex-specific estimates of the probability of cancer overall and aggressive cancer among patients with a kidney mass in order to aid with initial decision-making.

Tubulocystic renal cell carcinoma: a review of literature focused on radiological findings for differential diagnosis

Tubulocystic renal cell carcinoma (TC-RCC) has been classified as an independent subtype according to the 2016 World Health Organization (WHO) classification. It is a rare subtype that predominantly affects men. Although few in number, radiological imaging reports have suggested that TC-RCC is characterized by multilocular cystic lesions, which are categorized as the Bosniak classification II-IV, with signature pathological characteristics comprising numerous small cysts or a tubular structure. The Bosniak classification system facilitates patient management; however, the differentiation of cystic tumors exhibiting similar imaging findings remains impossible; in fact, the differentiation of multilocular cystic RCC, adult cystic nephroma, and mixed epithelial and stromal tumor remains challenging. This review aims to discuss TC-RCC with a focus on implications of radiological findings in the differential diagnosis of TC-RCC.

Tubulocystic Carcinoma of the Bile Duct

Tubulocystic carcinoma of the bile duct is extremely rare and has not been reported in the literature. We reported a case of cystic neoplasm of the liver with distinct histopathological features that could not be clearly classified as of either mucinous or intraductal papillary neoplasm. A 68-year-old Japanese patient had a multicystic biliary tumor within the liver. This tumor was detected on follow-up of polymyalgia rheumatica. The exophytic, multicystic, 35 × 50 mm mass was composed of complex tubulocystic structures. We initially suspected cystadenocarcinoma of the liver and performed radical operation. However, pathology ultimately showed it to be very rare tubulocystic carcinoma that derived from the bile duct. We reviewed the literature and describe the process of our differential diagnosis.

High grade infiltrative adenocarcinomas of renal cell origin: New insights into classification, morphology, and molecular pathogenesis

Collecting duct carcinoma was described over 30 years ago as a renal tumor, based in the medullary collecting system, with tubulopapillary morphology, prominent infiltrative growth, and stromal desmoplasia. While diagnostic workup has always emphasized exclusion of upper tract urothelial carcinoma and metastatic adenocarcinoma to the kidney, the molecular era of renal cell carcinoma classification has enabled recognition of and provided tools for diagnosis of new entities in this morphologic differential. In this review, we consider these developments, with emphasis on renal medullary carcinoma, closely related renal cell carcinoma, unclassified with medullary phenotype, and fumarate hydratase-deficient renal cell carcinoma. Integration of ancillary studies with suggestive patterns of morphology is emphasized for practical implementation in contemporary diagnosis, and several emerging tumor types in the morphologic differential are presented.

Fine-needle aspiration of tubulocystic renal cell carcinoma

We report two cases of tubulocystic renal cell carcinoma, a rare renal tumor the cytology of which has not been previously reported. Both aspirates were cellular and contained large sheets of cells with abundant granular cytoplasm, distinct cell borders and intracellular windows, distinct to prominent nucleoli, rare intracytoplasmic vacuoles, and rare nuclear grooves. Cells with variable amounts of cytoplasm were also arranged in small groups, some of which resembled spherules. The large sheets of cells with windows appeared specific for tubulocystic carcinoma; the spherules could easily be confused with a papillary renal cell carcinoma.

Rare urologic tumors

PURPOSE OF REVIEW

Management of genitourinary malignancy is likely to encompass a large portion of most of the urologist's practice. The challenge for the modern urologist is not only in understanding the management of commonly seen genitourinary malignancies, but also in recognizing unusual variants and their differences in management. This is evermore important as new technologies have refined the ability to identify rare entities. This review presents a brief overview of the various genitourinary malignancy subtypes seen within urology.

RECENT FINDINGS

All major organ subtypes are highlighted along with an overview of the current understanding of their associated malignancies. An update on the current state management paradigms as well as future directions is also outlined.

SUMMARY

After reading this review, the urologist should have a deeper understanding of the breadth of disorders in genitourinary oncology and a clearer approach to the management of these problems. Additionally, ongoing avenues for research are highlighted.

Noncoding RNA Expression and Targeted Next-Generation Sequencing Distinguish Tubulocystic Renal Cell Carcinoma (TC-RCC) from Other Renal Neoplasms

Tubulocystic renal cell carcinoma (TC-RCC) is a rare recently described renal neoplasm characterized by gross, microscopic, and immunohistochemical differences from other renal tumor types and was recently classified as a distinct entity. However, this distinction remains controversial particularly because some genetic studies suggest a close relationship with papillary RCC (PRCC). The molecular basis of this disease remains largely unexplored. We therefore performed noncoding (nc) RNA/miRNA expression analysis and targeted next-generation sequencing mutational profiling on 13 TC-RCC cases (11 pure, two mixed TC-RCC/PRCC) and compared with other renal neoplasms. The expression profile of miRNAs and other ncRNAs in TC-RCC was distinct and validated 10 differentially expressed miRNAs by quantitative RT-PCR, including miR-155 and miR-34a, that were significantly down-regulated compared with PRCC cases (n = 22). With the use of targeted next-generation sequencing we identified mutations in 14 different genes, most frequently (>60% of TC-RCC cases) in ABL1 and PDFGRA genes. These mutations were present in <5% of clear cell RCC, PRCC, or chromophobe RCC cases (n > 600) of The Cancer Genome Atlas database. In summary, this study is by far the largest molecular study of TC-RCC cases and the first to investigate either ncRNA expression or their genomic profile. These results add molecular evidence that TC-RCC is indeed a distinct entity from PRCC and other renal neoplasms.

Is Tubulocystic Renal Cell Carcinoma Real?: Genomic Analysis Confirms the World Health Organization Classification

This commentary highlights the article by Lawrie et al that validates that tubulocystic renal cell carcinoma is a distinct type of renal neoplasm.

Renal Cell Tumors: Understanding Their Molecular Pathological Epidemiology and the 2016 WHO Classification

Accumulating evidence suggests that renal cell tumors represent a group of histologically and molecularly heterogeneous diseases, even within the same histological subtype. In accordance with the increased understanding of the morphological, immunohistochemical, molecular, and epidemiological characteristics of renal cell tumors, the World Health Organization (WHO) classification of renal cell tumors has been modified. This review provides perspectives on both new and current subtypes of renal cell tumors, as well as on the emerging/provisional renal cell carcinomas in the new 2016 WHO classification, which focuses on features of their molecular pathological epidemiology. The WHO classification will require additional revisions to enable the classification of renal cell tumors as clinically meaningful subtypes and provide a better understanding of the unique characteristics of renal cell tumors.

Molecular Genetic Alterations in Renal Cell Carcinomas With Tubulocystic Pattern: Tubulocystic Renal Cell Carcinoma, Tubulocystic Renal Cell Carcinoma With Heterogenous Component and Familial Leiomyomatosis-associated Renal Cell Carcinoma. Clinicopathologic and Molecular Genetic Analysis of 15 Cases

The characteristic morphologic spectrum of tubulocystic renal cell carcinoma (TC-RCC) may include areas resembling papillary RCC (PRCC). Our study includes 15 RCCs with tubulocystic pattern: 6 TC-RCCs, 1 RCC-high grade with tubulocystic architecture, 5 TC-RCCs with foci of PRCC, 2 with high-grade RCC (HGRCC) not otherwise specified, and 1 with a clear cell papillary RCC/renal angiomyoadenomatous tumor-like component. We analyzed aberrations of chromosomes 7, 17, and Y; mutations of VHL and FH genes; and loss of heterozygosity at chromosome 3p. Genetic analysis was performed separately in areas of classic TC-RCC and in those with other histologic patterns. The TC-RCC component demonstrated disomy of chromosome 7 in 9/15 cases, polysomy of chromosome 17 in 7/15 cases, and loss of Y in 1 case. In the PRCC component, 2/3 analyzable cases showed disomy of chromosome 7 and polysomy of chromosome 17 with normal Y. One case with focal HGRCC exhibited only disomy 7, whereas the case with clear cell papillary RCC/renal angiomyoadenomatous tumor-like pattern showed polysomies of 7 and 17, mutation of VHL, and loss of heterozygosity 3p. FH gene mutation was identified in a single case with an aggressive clinical course and predominant TC-RCC pattern. The following conclusions were drawn: (1) TC-RCC demonstrates variable status of chromosomes 7, 17, and Y even in cases with typical/uniform morphology. (2) The biological nature of PRCC/HGRCC-like areas within TC-RCC remains unclear. Our data suggest that heterogenous TC-RCCs may be associated with an adverse clinical outcome. (3) Hereditary leiomyomatosis-associated RCC can be morphologically indistinguishable from "high-grade" TC-RCC; therefore, in TC-RCC with high-grade features FH gene status should be tested.

Imaging features of papillary renal cell carcinoma with cystic change-dominant appearance in the era of the 2016 WHO classification

PURPOSE

Papillary renal cell carcinoma (P-RCC) typically exhibits a homogeneous, solid hypovascular mass; P-RCC with a cystic appearance is atypical. Tubulocystic RCC (TC-RCC), a newly proposed entity for renal tumors in the 2016 WHO classification, and cystic papillary RCC, may yield similar imaging findings. Therefore, we investigated the incidence of papillary RCC with cystic changes and compared its CT and pathologic features to differentiate between two entities.

METHODS

We retrospectively evaluated 26 consecutive patients diagnosed with P-RCC. Two radiologists consensually identified dominant masses indicative of cystic changes on CT scans and recorded their Bosniak classification. In addition, two pathologists inspected the whole area of tumors macroscopically, labeled them as solid- or cystic change-dominant tumors, determined the pathogenesis of the cystic components (necrosis or hemorrhage), and recorded their inherent cystic characteristics (with/without TC-RCC components). We defined masses with cystic changes involving more than 50% of the entire tumor as cystic change-dominant tumors.

RESULTS

Of the 26 tumors, 7 (27%) were diagnosed cystic change-dominant based on imaging and pathologic findings, of these, 2 were classified as Bosniak type III and 5 as Bosniak type IV. The pathologists confirmed that two type IV tumors demonstrated extensive necrosis and one type IV tumor revealed extensive hemorrhage. Four P-RCCs (type III and IV, 2 each) were of a mixed type harboring both solid and cystic components. Only one tumor exhibited a multilocular cystic appearance. All 7 cystic change-dominant P-RCCs were pathologically diagnosed as a pure P-RCC without TC-RCC components.

CONCLUSION

While P-RCCs may contain cystic features, the multilocular type of cystic P-RCC is rare.

Morphologic, Molecular, and Taxonomic Evolution of Renal Cell Carcinoma: A Conceptual Perspective With Emphasis on Updates to the 2016 World Health Organization Classification

Molecular and morphologic interrogation has driven a much-needed reexamination of renal cell carcinoma (RCC). Indeed, the recently released 2016 World Health Organization classification now recognizes 12 distinct RCC subtypes, as well as several other emerging/provisional RCC entities. From a clinical perspective, accurate RCC classification may have important implications for patients and their families, including prognostic risk stratification, targeted therapeutics selection, and identification for genetic testing. In this review, we provide a conceptual framework for approaching RCC diagnosis and classification by categorizing RCCs as tumors with clear cytoplasm, papillary architecture, and eosinophilic (oncocytic) cytoplasm. The currently recognized 2016 World Health Organization classification for RCC subtypes is briefly discussed, including new diagnostic entities (clear cell papillary RCC, hereditary leiomyomatosis and RCC-associated RCC, succinate dehydrogenase-deficient RCC, tubulocystic RCC, and acquired cystic disease-associated RCC) and areas of evolving RCC classification, such as transcription elongation factor B subunit 1 (TCEB1)-mutated RCC/RCC with angioleiomyoma-like stroma/RCC with leiomyomatous stroma, RCC associated with anaplastic lymphoma receptor tyrosine kinase (ALK) gene rearrangement, thyroidlike follicular RCC, and RCC in neuroblastoma survivors. For each RCC subtype, relevant clinical, molecular, gross, and microscopic findings are reviewed, and ancillary studies helpful for its differential diagnosis are presented, providing a practical approach to modern RCC classification.