Toward Biological Subtyping of Papillary Renal Cell Carcinoma With Clinical Implications Through Histologic, Immunohistochemical, and Molecular Analysis

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

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

[2022 WHO classification of renal cell carcinomas: Focus on papillary renal cell carcinoma]

Renal cell carcinomas (RCC) represent a group of heterogeneous tumors whose classification has greatly evolved since 1981. The latest update in 2022 classifies all renal cell carcinomas into six categories according to their morphology or the detection of specific molecular alterations. Molecular disassembly of renal cell carcinomas with papillary features has enabled the identification of new entities characterized by a specific molecular alteration, such as Fumarate Hydratase (FH) deficient RCC, TFE3-rearranged RCC or TFEB-altered RCC. This new classification allows for a more accurate diagnosis but requires a thorough knowledge of the genomic alterations to search for with immunohistochemical or molecular biology techniques. According to the new WHO 2022 classification, papillary renal cell carcinoma (PRC) type 1 or type 2 classification is no longer recommended. A classification based on nucleolar ISUP grade must be preferred: low-grade PRC (ISUP 1-2) or high-grade PRC (ISUP 3-4). The other prognostic factors remain the same: the pTNM stage, lymphovascular invasion, and the presence or absence of dedifferentiated areas referring to sarcomatoid or rhabdoid features. Of note, the presence of necrosis is not currently recognized as a poor prognostic element for this type of carcinoma. The diagnosis of high-grade PRC is from now on a diagnosis of exclusion. It can only be sustained after having ruled out TFE3-rearranged RCC, TFEB-altered RCC, and FH-deficient RCC. For clinicians, the diagnosis of PRC implies suggesting an oncogenetic consultation to screen for an associated genetic tumor syndrome regardless of the patient's age.

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

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

Papillary renal neoplasm with reverse polarity is biologically and clinically distinct from eosinophilic papillary renal cell carcinoma

Papillary renal neoplasm with reverse polarity (PRNRP) is a recently described indolent entity with distinct features and its recognition from other oncocytic/eosinophilic papillary renal cell carcinoma (ePRCC) has important prognostic implications. ABCC2, a renal drug transporter, is overexpressed in aggressive PRCCs. In this study, we compared the clinicopathological parameters and the biological ABCC2 expression between PRNRP and ePRCC. PRNRP (n = 8) and ePRCC (n = 21) cases were selected from resection specimens and corresponding clinicopathological data were collected. ABCC2 immunohistochemical (IHC) staining was performed and ABCC2 staining patterns were classified as negative, cytoplasmic, and brush-border. RNA in-situ hybridization (ISH) was used to assess ABCC2 transcript levels. All eight PRNRP cases had weak cytoplasmic ABCC2 IHC reactivity; however, they showed no detectable ABCC2 transcripts on RNA ISH. In comparison, 76% (16/21) of ePRCCs showed ABCC2 IHC brush-border expression and significantly higher ABCC2 RNA ISH transcript levels (p < 0.001). Additionally, the ePRCC group showed a significantly larger tumor size (p = 0.004), higher WHO/ISUP grade (p < 0.001), and stage (p = 0.044). None of the PRNRP cases showed disease progression, while 9.5% (2/21) ePRCCs had disease progression. PRNRP is clinically and biologically distinct from ePRCC. Hence, it is crucial to differentiate between these two entities, particularly in needle core biopsies.

[Papillary renal neoplasm with reverse polarity]

Papillary renal neoplasm with reverse polarity is a rare subtype of papillary renal cell tumors with unique morphology, specific molecular features and good prognosis. The article presents literature data and describes our own observation of a papillary kidney tumor with reverse nuclear polarity in a 73-year-old patient. The difficulties of preoperative diagnosis of a tumor are shown, histological and immunohistochemical criteria for diagnosis and differential diagnosis of this tumor with other kidney tumors are presented. This rare case is of interest for both pathologists and clinicians.

ABCC2 brush-border expression predicts outcome in papillary renal cell carcinoma: a multi-institutional study of 254 cases

AIMS

Papillary renal cell carcinoma (PRCC) histologic subtyping is no longer recommended in the 2022 WHO classification. Currently, WHO/ISUP nucleolar grade is the only accepted prognostic histologic parameter for PRCC. ABCC2, a renal drug transporter, has been shown to significantly predict outcomes in PRCC. In this study we evaluated the prognostic significance of ABCC2 IHC staining patterns in a large, multi-institutional PRCC cohort and assessed the association of these patterns with ABCC2 mRNA expression.

METHODS AND RESULTS

We assessed 254 PRCCs for ABCC2 IHC reactivity patterns that were stratified into negative, cytoplasmic, brush-border <50%, and brush-border ≥50%. RNA in situ hybridization (ISH) was used to determine the transcript level of each group. Survival analysis was performed with SPSS and GraphPad software. RNA-ISH showed that the ABCC2 group with any brush-border staining was associated with a significant increase in the transcript level, when compared to the negative/cytoplasmic group (P = 0.034). Both ABCC2 groups with brush-border <50% (P = 0.024) and brush-border ≥50% (P < 0.001) were also associated with worse disease-free survival (DFS) in univariate analysis. Multivariate analysis showed that only ABCC2 IHC brush-border (<50% and ≥50%) reactivity groups (P = 0.037 and P = 0.003, respectively), and high-stage disease (P < 0.001) had a DFS of prognostic significance. In addition, ABCC2 brush-border showed significantly worse DFS in pT1a (P = 0.014), pT1 (P = 0.013), ≤4 cm tumour (P = 0.041) and high stage (P = 0.014) groups, while a similar analysis with high WHO/ISUP grade in these groups was not significant.

CONCLUSION

ABCC2 IHC brush-border expression in PRCC correlates with significantly higher gene expression and also independently predicts survival outcomes.

Ipsilateral synchronous papillary renal neoplasm with reverse polarity and urothelial carcinoma in a renal transplant recipient: a rare case report with molecular analysis and literature review

BACKGROUND

Renal transplant recipients (RTRs) have a 3- to 5-fold higher risk of developing malignant tumors than the general population, with new malignant tumors after transplantation considered to be the leading cause of death in RTRs. In pathological practice, it is rare for neoplasms with different histology to be located in the same organ. We report the first case of a synchronous papillary renal neoplasm with reverse polarity (PRNRP) and urothelial carcinoma (UC) in the ipsilateral kidney in an RTR. Molecular detection was conducted by next-generation sequencing.

CASE PRESENTATION

A 68-year-old female suffered from uremia 19 years ago and underwent renal transplantation (RT) after receiving dialysis for 6 months. Hematuria occurred one month ago and an enhanced CT showed that there were two abnormal density foci in the middle and lower parts of the autologous left kidney. A laparoscopic left nephrectomy and ureterectomy were performed. Gross examination revealed a mass (I) in the left renal parenchyma, 2*1.8*1.5 cm in size, that protruded from the renal capsule, and a cauliflower-like mass (II), 5*2.5*2 cm in size, adjacent to the mass (I). Microscopic findings revealed these lesions were PRNRP and UC, respectively. PCR analysis revealed a KRAS gene mutation (G12D in exon 2) in the PRNRP, while NGS analysis revealed FGFR3 (S249C in exon 7) and KDM6A (Q271Ter in exon 10 and A782Lfs in exon 17) mutations in the UC.

CONCLUSIONS

We report here for the first time an extraordinarily rare case of synchronous renal tumors of a PRNRP and UC in the ipsilateral kidney of an RTR. We identified simultaneous KRAS, FGFR3, and KDM6A mutations in two different renal masses in the ipsilateral kidney. Pathologic assessment with comparative molecular analysis of mutational profiles facilitates tumor studies after RT and may be of great value in clinical management strategies.

Drug transporters in drug disposition - the year 2022 in review

On behalf of all the authors, I am pleased to share our third annual review on drug transporter science with an emphasis on articles published and deemed influential in signifying drug transporters' role in drug disposition in the year 2022. As the drug transporter field is rapidly evolving several key findings were noted including promising endogenous biomarkers, rhythmic activity, IVIVE approaches in transporter-mediated clearance, new modality interaction, and transporter effect on gut microbiome. As identified previously (Chothe et Cal. 2021, 2022) the goal of this review is to highlight key findings without a comprehensive overview of each article and to this end, each coauthor independently selected 1-3 peer-reviewed articles published or available online in the year 2022 (Table 1). Each article is summarized in synopsis and commentary with unbiased viewpoints by each coauthor. We strongly encourage readers to consult original articles for specifics of the study. Finally, I would like to thank all coauthors for their continued support in writing this annual review on drug transporters and invite anyone interested in contributing to future versions of this review.

Comparison and validation of different risk models for papillary renal cell carcinoma

BACKGROUND

Several prognostic algorithms were specifically or nonspecifically used for papillary renal cell carcinoma (PRCC). No consensus was reached upon their efficacy of discrimination. We aim to compare the stratifying ability of current models or systems in predicting the risk of recurrence of PRCC.

METHODS

A PRCC cohort consisting of 308 patients from our institution and 279 patients from The Cancer Genome Atlas (TCGA) was generated. With ISUP grade, TNM classification, UCLA Integrated Staging System (UISS), STAGE, SIZE, GRADE AND NECROSIS (SSIGN), Leibovich model and VENUSS system, recurrence-free survival (RFS), disease-specific survival (DSS) and overall survival (OS) were studied using Kaplan-Meier method and concordance index (c-index) was compared. Differences between risk groups in gene mutation and infiltration of inhibitory immune cells were studied with TCGA database.

RESULTS

All the algorithms were able to stratify patients in RFS as well as DSS and OS (all P < 0.001). VENUSS score and risk group generally had the highest and balanced c-index (0.815 and 0.797 for RFS). ISUP grade, TNM stage and Leibovich model had the lowest c-indexes in all analysis. Among the 25 most frequently mutated genes in PRCC, eight had different mutation frequency between VENUSS low- and intermediate-/high-risk patients and mutated KMT2D and PBRM1 resulted in worsened RFS (P = 0.053 and P = 0.007). Increased Treg cells in tumors of intermediate-/high- risk patients were also identified.

CONCLUSIONS

VENUSS system showed better predictive accuracy in RFS, DSS and OS compared with SSIGN, UISS and Leibovich risk models. VENUSS intermediate-/high-risk patients had increased frequency of mutation in KMT2D and PBRM1 and increased infiltration of Treg cells.

Rare papillary renal neoplasm with reverse polarity: A case report and review of the literature

Papillary renal neoplasm with reverse polarity (PRNRP) is a rare renal tumour and was newly named in 2019. This study reported a case of a 30-year-old female patient with a left renal tumour without any clinical symptoms and whose CT scan of her left kidney showed a mass of 2.6 cm×2.3 cm, which was considered to be renal clear cell carcinoma. Laparoscopic partial nephrectomy was performed, and histopathology and immunohistochemistry confirmed papillary renal neoplasm with reverse polarity, which had unique clinicopathological features, immunophenotype, KRAS gene mutation and relatively indolent biological behaviour. As newly diagnosed cases, rigorous and regular follow-up is necessary. In addition, a literature review was performed from 1978 to 2022, and 97 cases of papillary renal neoplasms with reverse polarity were identified and analysed.

TFE3-immunopositive papillary renal cell carcinoma: A clinicopathological, immunohistochemical, and genetic study

It is possible that PRCCs may still contain a variety of unknown histologic subtypes. Some PRCCs express high expression of TFE3 protein without TFE3 gene rearrangement, but no reports have investigated the significance of this. Here we attempted to examine clinicopathological and molecular significance of the TFE3-immunopositive PRCC. We reviewed the histology and immunohistochemistry in 58 PRCCs. TFE3 immunoexpression was recognized in 7 cases. Because TFE3 immunostaining shows false-positive, to ensure the integrity of TFE3 immunostaining, the immunostaining was performed under strict control of internal controls and western blotting was performed on 2 positive cases and 5 negative cases, and differences in protein expression between two groups were confirmed. Significant immunohistochemical expressions of autophagy/lysosome proteins were observed in TFE3-positive group. No TFE3 gene arrangement was detected in all positive cases by fluorescence in situ hybridization. Whole-exome sequencing was performed on 6 TFE3-positive and 2 TFE3-negative cases. Gain of chromosome 7 was found in five of 6 TFE3-positive cases (83%). TFE3-positive group was correlated significantly with higher pTstage, cNstage, WHO/ISUP nuclear grade, and decreased OS. TFE3-immunopositive PRCC group had a poorer prognosis than TFE3-negative PRCC group and showed correlation with expressions of autophagy/lysosome proteins, suggesting that enhancement of autophagy/lysosome function drives an environment of energy metabolism that is favorable for cancer. It is necessary to recognize that there is TFE3-immunopositive group without TFE3 gene rearrangement within PRCC. Because of its aggressive biological behaviour, TFE3 can act as a biomarker in PRCC; moreover, autophagy-inhibiting drugs may have therapeutic effects on TFE3-immunopositive PRCC.

Tumors masquerading as type 2 papillary renal cell carcinoma: pathologists' ever-expanding differential diagnosis for a heterogeneous group of entities

Although papillary renal cell carcinoma has historically been classified as either type 1 or type 2, data from The Cancer Genome Atlas (TCGA) has demonstrated significant genomic heterogeneity in tumors classified as "type 2 papillary renal cell carcinoma" (T2PRCC). Papillary renal cell carcinoma is expected to have a favorable clinical course compared to clear cell renal cell carcinoma (CCRCC). However, tumors with poor outcome more similar to CCRCC were included in the T2PRCC cohort studied by the TCGA. The differential diagnosis for T2PRCC includes a variety of other renal tumors, including aggressive entities such as TFE3 translocation-associated renal cell carcinoma, TFEB-amplified renal cell carcinoma, fumarate hydratase-deficient renal cell carcinoma, high-grade CCRCC, and collecting duct carcinoma. Accurate classification of these tumors is important for prognostication and selection of therapy.

How New Developments Impact Diagnosis in Existing Renal Neoplasms

In recent years, several emerging diagnostic entities have been described in renal cell carcinoma (RCC). However, our understanding of well-known and established entities has also grown. Clear cell papillary RCC is now relabeled as a tumor rather than carcinoma in view of its nonaggressive behavior. Renal tumors with a predominantly infiltrative pattern are very important for recognition, as most of these have aggressive behavior, including fumarate hydratase-deficient RCC, SMARCB1-deficient medullary carcinoma, collecting duct carcinoma, urothelial carcinoma, and metastases from other cancers.

Contemporary Clinical Definitions, Differential Diagnosis, and Novel Predictive Tools for Renal Cell Carcinoma

Despite significant progress regarding clinical detection/imaging evaluation modalities and genetic/molecular characterization of pathogenesis, advanced renal cell carcinoma (RCC) remains an incurable disease and overall RCC mortality has been steadily rising for decades. Concomitantly, clinical definitions have been greatly nuanced and refined. RCCs are currently viewed as a heterogeneous series of cancers, with the same anatomical origin, but fundamentally different metabolisms and clinical behaviors. Thus, RCC pathological diagnosis/subtyping guidelines have become increasingly intricate and cumbersome, routinely requiring ancillary studies, mainly immunohistochemistry. Meanwhile, RCC-associated-antigen targeted systemic therapy has been greatly diversified and emerging, novel clinical applications for RCC immunotherapy have already reported significant survival benefits, at least in the adjuvant setting. Even so, systemically disseminated RCCs still associate very poor clinical outcomes, with currently available therapeutic modalities only being able to prolong survival. In lack of a definitive cure for advanced RCCs, integration of the amounting scientific knowledge regarding RCC pathogenesis into RCC clinical management has been paramount for improving patient outcomes. The current review aims to offer an integrative perspective regarding contemporary RCC clinical definitions, proper RCC clinical work-up at initial diagnosis (semiology and multimodal imaging), RCC pathological evaluation, differential diagnosis/subtyping protocols, and novel clinical tools for RCC screening, risk stratification and therapeutic response prediction.

Papillary renal neoplasm with reverse polarity-a comparative study with CCPRCC, OPRCC, and PRCC1

Papillary renal neoplasm with reverse polarity (PRNRP) is a newly defined entity with distinct histomorphology and recurrent KRAS mutation. In this study, we aimed to identify and analyze the clinicopathological, immunohistochemical (IHC), and molecular features of PRNRP in our center and to evaluate its differential diagnosis with other tumors with which it is easily confused: clear cell papillary renal cell carcinoma (CCPRCC), oncocytic papillary renal cell carcinoma (OPRCC), and papillary renal cell carcinoma type 1 (PRCC1). Nephrectomy specimens of PRNRP (n = 15), CCPRCC (n = 11), and OPRCC (n = 12) were retrieved from our pathology archives. We also selected typical cases of PRCC1 (n = 15) as a control group. PRNRP accounted for 3.05% (15/492) of all PRCC cases at our center. The median follow-up period was 41.3 months. All PRNRP cases were pT1N0M0, and only one involved recurrence (1 year after surgery). IHC analysis showed diffuse staining of CK7, EMA, and GATA3 but weak or negative staining of CD10, CD117, p504s, and vimentin in the PRNRP samples and distinctive IHC features in the other three tumor types. KRAS mutation was detected in 4/10 PRNRP cases. Among the 40 most commonly mutated genes identified, 5 (BCLAF1, PDE4DIP, NCOR1, PARP4, and PABPC1) have actionable alterations. Our study supports the suggestion that PRNRP is an entity distinct from CCPRCC, OPRCC, and PRCC1.

WHO 2022 landscape of papillary and chromophobe renal cell carcinoma

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

Recurrent KRAS mutations are early events in the development of papillary renal neoplasm with reverse polarity

We evaluated the clinicopathologic and molecular characteristics of mostly incidentally detected, small, papillary renal neoplasms with reverse polarity (PRNRP). The cohort comprised 50 PRNRP from 46 patients, divided into 2 groups. The clinically undetected (<5 mm) neoplasms (n = 34; 68%) had a median size of 1.1 mm (range 0.2-4.3 mm; mean 1.4 mm), and the clinically detected (≥5 mm) neoplasms (n = 16; 32%) which had a median size of 13 mm (range 9-30 mm; mean 16 mm). Neoplasms were positive for GATA3 (n = 47; 100%) and L1CAM (n = 34/38; 89%) and were negative for vimentin (n = 0/44; 0%) and, to a lesser extent, AMACR [(n = 12/46; 26%; weak = 9, weak/moderate = 3)]. KRAS mutations were found in 44% (n = 15/34) of the clinically undetected PRNRP and 88% of the clinically detected PRNRP (n = 14/16). The two clinically detected PRNRP with wild-type KRAS gene were markedly cystic and contained microscopic intracystic tumors. In the clinically undetected PRNRP, the detected KRAS mutations rate was higher in those measuring ≥1 mm vs <1 mm [n = 14/19 (74%) vs n = 1/15 (7%)]. Overall, the KRAS mutations were present in exon 2-codon 12: c.35 G > T (n = 21), c.34 G > T (n = 3), c.35 G > A (n = 2), c.34 G > C (n = 2) resulting in p.Gly12Val, p. Gly12Asp, p.Gly12Cys and p.Gly12Arg, respectively. One PRNRP had a G12A/V/D complex mutation. Twenty-six PRNRP were concurrently present with other tumors of different histologic subtypes in the ipsilateral kidney; molecular testing of 8 of the latter showed wild-type KRAS gene despite the presence of KRAS mutations in 5 concurrent PRNRP. On follow up, no adverse pathologic events were seen (range 1-160 months; mean 44 months). In conclusion, the presence of KRAS mutations in small, clinically undetected PRNRP provides a unique finding to this entity and supports its being an early event in the development of these neoplasms.

Papillary renal neoplasm with reverse polarity may be a novel renal cell tumor entity with low malignant potential

AIMS

This study retrospectively investigated the morphological, immunohistochemical and molecular genetic features of papillary renal neoplasm with reverse polarity (PRNRP), a recently described renal tumor.

METHODS AND RESULTS

Eleven cases of PRNRP were collected, and 16 cases of type I and 9 cases of type II papillary renal cell carcinoma were included as a control series. Pathological features were evaluated based on HE staining and immunohistochemistry. KRAS exon 2 and BRAF V600E mutations were detected by Real-time PCR and Sanger sequencing. Fluorescence in situ hybridization was conducted for identification of chromosomal abnormalities. Hemosiderin deposition was found in a small amount of tumor cells in 6 cases. Multifocal or patchy necrosis (5/11), small focal invasion of the pseudocapsules or renal parenchyma (6/11), and breakthrough of renal capsule with nerve invasion (1/11) were revealed, inconsistent with the previous view that the tumor lacks necrosis and intercellular hemosiderin. Immunohistochemical staining (diffusely positive for CK7 and GATA3, negative for CD117 and vimentin, and negative to weakly positive for P504S) and high frequency of KRAS mutations in exon 2 (9/10) supported the identification and inclusion of our cases. Chromosome 7 trisomy (1/7), chromosome 17 trisomy (0/7) and chromosome Y deletion (0/5 male patients) were seldom detected in this tumor. All patients were alive without metastasis or recurrence at the end of the follow-up.

CONCLUSION

Our findings may highlight the possibility of a low malignant potential of this emerging entity. We suggest that the tumor be classified as a novel renal cell tumor subtype independent of papillary renal cell carcinoma.

Papillary renal neoplasm with reverse polarity: A clinicopathological and molecular genetic characterization of 16 cases with expanding the morphologic spectrum and further support for a novel entity

Papillary renal neoplasm with reverse polarity (PRNRP) is a recently described, rare renal tumor that differs clinically, morphologically, and molecularly from papillary renal cell carcinoma (RCC). To further characterize the pathological spectrum of this rare tumor, in this study, we retrospectively identified 16 cases of PRNRP from three institutions to comprehensively investigate the clinicopathological and molecular genetic features, using immunohistochemistry (IHC), fluorescence in-situ hybridization (FISH), and targeted next-generation sequencing (NGS). The patients included nine men and seven women, with age ranging from 47 to 80 years (median = 67.5 years, mean = 65 years). The tumor size ranged from 0.4 to 9.5 cm in the greatest dimension (median = 1.8 cm, mean = 2.6 cm). Most tumors (12/16) were incidentally identified by imaging studies. By AJCC stage, 15 were categorized as pT1 and 1 was pT2. Follow-up showed no recurrences, metastases, or disease-related deaths in all the 16 patients. Grossly, 14 cases demonstrated at least a partially cystic appearance. Microscopically, all PRNRPs except 1 (case 13) were composed predominantly of thin, branching papillary architecture covered by a single layer of cuboidal cells with finely granular cytoplasm, and low-grade nuclei typically located toward the apical surface away from the basement. Case 13 consisted mostly of solid, densely packed tubules with only a minor papillary component (5%). Other commonly seen histological features included hyalinized or edematous papillae (n = 11), lymphocyte aggregation in fibrovascular cores (n = 10), mast cell infiltration (n = 8), and intralesional hemorrhage (n = 7). Uncommonly seen histological features included lymphoid cuff (n = 4), hemosiderin deposition (n = 5), foci of clear cell change (n = 4), intracytoplasmic vacuoles (n = 4), eosinophilic hobnail cells (n = 2), and infarct-type necrosis (n = 1). Two PRNRPs were concurrent with ipsilateral clear cell papillary RCC and clear cell RCC, respectively. By IHC, the tumors were consistently positive for GATA3, CK7, and PAX8. Fourteen out of 16 tumors showed a basolateral-membranous E-cadherin expression pattern, and 12/16 cases were positive for 34βE12.The expression of AMACR, CD10, and vimentin was either absent or only weak and focal. By targeted NGS, 13/14 evaluated PRNRPs harbored KRAS missense mutations involving c.35G>T resulting in p.G12V (7/13), c.35G>A resulting in p.G12D (4/13), and c.34G>T resulting in p.G12C (2/13). By FISH, 1/15 had gains of chromosomes 7 and 17, and 2/8 male cases had deletion of chromosomes Y. In conclusion, our study confirms that PRNRP is an indolent renal cell neoplasm with unique morphology, consistent immunohistochemical profile, and recurrent KRAS mutation. Our study expands the morphologic spectrum of PRNRP and provides further evidence supporting it as a novel entity.

Papillary renal cell carcinoma: current and controversial issues

PURPOSE OF THE REVIEW

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

RECENT FINDINGS

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

SUMMARY

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

Papillary renal cell carcinoma: a single institutional study of 199 cases addressing classification, clinicopathologic and molecular features, and treatment outcome

The morphologic spectrum of type 1 papillary renal cell carcinoma (PRCC) is not well-defined, since a significant proportion of cases have mixed type 1 and 2 histology. We analyzed 199 cases of PRCC with any (even if focal) type 1 features, with a median follow-up of 12 years, to identify clinicopathological features associated with outcome. Ninety-five tumors (48%) of the cohort contained some type 2 component (median amount: 25%; IQR: 10%, 70%). As a group they showed high rates of progression-free (PFS) and cancer-specific survival (CSS). Tumor size, mitotic rate, lymphovascular invasion, sarcomatoid differentiation, sheet-like architecture, and lack of tumor circumscription were significantly associated with CSS (p ≤ 0.015) on univariate analysis. While predominant WHO/ISUP nucleolar grade was associated with PFS (p = 0.013) and CSS (p = 0.030), the presence of non-predominant (<50%) nucleolar grade did not show association with outcome (p = 0.7). PFS and CSS showed no significant association with the presence or the amount of type 2 morphology. We compared the molecular alterations in paired type 1 and type 2 areas in a subset of 22 cases with mixed type 1 and 2 features and identified 12 recurrently mutated genes including TERT, ARID1A, KDM6A, KMT2D, NFE2L2, MET, APC, and TP53. Among 78 detected somatic mutations, 61 (78%) were shared between the paired type 1 and type 2 areas. Copy number alterations, including chromosome 7 and 17 gains, were similar between type 1 and 2 areas. These findings support that type 2 features in a PRCC with mixed histology represent either morphologic variance or clonal evolution. Our study underscores the notion that PRCC with any classic type 1 regions is best considered as type 1 PRCC and assigned the appropriate WHO/ISUP nucleolar grade. It provides additional evidence that type 2 PRCC as a separate category should be re-assessed and likely needs to be abandoned.

Papillary Renal Cell Carcinomas Demonstrating Micropapillary Features: An Investigation Into the Diagnostic and Prognostic Implications

Aims: Papillary renal cell carcinoma (PRCC) with micropapillary carcinoma (MC) has been rarely described. We conducted a retrospective descriptive evaluation of the association of MC with PRCC and the possible prognostic implications.

Methods: A database search was made at the University of Southern California (USC) and Lenox Hill Hospital (LHH; New York City) in June 2016-June 2019 of PRCC cases with MC. Diagnosis of MC was made using routine histology, based on the presence of small clusters of cells without a vascular core. Features evaluated included: percent of MC, gross appearance, PRCC typing, nuclear grade, lymphovascular invasion, and lymph node metastasis.

Results: 848 RCC cases (690 from USC and 157 from LHH); 70 cases PRCC (54 from USC, 16 from LHH) of these cases, 13 had an MC, 12 were from radical nephrectomy, and 12 cases were male. Mean age was 68.3 years; seven were located in the right kidney. Average tumor size was 8.6 cm. MC ranged from 10% to 80% (average 37.5%), nine cases were PRCC type 2 and four type 1. Nuclear grade: three cases (grade 2), nine cases (grade 3), and one case (grade 4); 11 out of 13 tumors presented with extrarenal extension; nine cases that had lymph nodes submitted had metastatic carcinoma.

Conclusions: The presence of a micropapillary component in PRCC was found to be 18.5%, and it was predominantly associated with high pathologic stage and lymph node metastases. The clinical course of these tumors seems similar to MC in other tissues/organ systems. We advocate reporting this pattern when identified.

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

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

The Morphological Spectrum of Papillary Renal Cell Carcinoma and Prevalence of Provisional/Emerging Renal Tumor Entities with Papillary Growth

Renal cell carcinoma (RCC) represents a heterogeneous disease, encompassing an increasing number of tumor subtypes. Post-2016, the World Health Organization (WHO) classification recognized that the spectrum of papillary renal cell carcinoma is evolving and has long surpassed the dichotomic simplistic "type 1 versus type 2" classification. The differential diagnosis of pRCC includes several new provisional/emerging entities with papillary growth. Type 2 tumors have been cleared out of several confounding entities, now regarded as independent tumors with specific clinical and molecular backgrounds. In this work we describe the prevalence and characteristics of emerging papillary tumor entities in two renal tumor cohorts (one consisting of consecutive papillary tumors from a single institute, the other consisting of consultation cases from several centers). After a review of 154 consecutive pRCC cases, 58% remained type 1 pRCC, and 34% type 2 pRCC. Papillary renal neoplasm with reversed polarity (1.3%), biphasic hyalinizing psammomatous RCC (1.3%), and biphasic squamoid/alveolar RCC (4.5%) were rare. Among 281 consultation cases, 121 (43%) tumors had a dominant papillary growth (most frequently MiT family translocation RCCs, mucinous tubular and spindle cell carcinoma and clear cell papillary RCC). Our data confirm that the spectrum of RCCs with papillary growth represents a major diagnostical challenge, frequently requiring a second expert opinion. Papillary renal neoplasm with reversed polarity, biphasic hyalinizing psammomatous RCC, and biphasic squamoid/alveolar RCC are rarely sent out for a second opinion, but correct classification and knowledge of these variants will improve our understanding of the clinical behavior of renal tumors with papillary growth.

Whether histologic subtyping affect the oncological outcomes of patients with papillary renal cell carcinoma: evidence from a systematic review and meta-analysis

Background

Whether the histologic subtype (type 1 and type 2) of papillary renal cell carcinoma (pRCC) is a tool to predict the prognosis is of great debate. This study is aimed to evaluate the prognostic significance of histologic subtype in patients with pRCC after surgery through a systematic review and meta-analysis.

Methods

We searched PubMed, the Web of Science, Cochrane library and EMBASE databases to identify studies published until January 20, 2021 according to the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines. Studies were deemed eligible if they compared the overall survival (OS), cancer specific survival (CSS), recurrence-free survival (RFS) or disease-free survival (DFS) between patients with type 1 or type 2 pRCC. And the corresponding hazard ratios (HRs) and 95% conference intervals (CIs) were collected for meta-analysis and further subgroup analysis.

Results

Overall 22 studies with a total of 4,494 patients were considered eligible and included for the systematic review and meta-analysis. The pooled results showed that type 2 pRCC was associated with a worse OS (pooled HR 1.61, 95% CI: 1.10–2.36, P=0.02) and CSS (pooled HR 1.59, 95% CI: 1.00–2.51, P=0.05). However, the subgroup analysis yielded the same result as the initial analysis only when the HRs were extracted from univariate analysis. In studies with multivariate analysis, type 2 pRCC was not statistically associated with a worse OS (pooled HR 1.22, 95% CI: 0.97–1.53, P=0.27), CSS (pooled HR 1.16, 95% CI: 0.67–2.00, P=0.60), and DFS (pooled HR 1.33, 95% CI: 0.93–1.91, P=0.12) compared to type 1 pRCC.

Discussion

Histologic subtype is not an independent prognostic factor for patients with pRCC, although the result needs to be taken with caution. And studies with retrospective study design, larger sample size and longer follow-up period are required to verify these results.

Prediction of histologic grade and type of small (< 4 cm) papillary renal cell carcinomas using texture and neural network analysis: a feasibility study

OBJECTIVE

To predict the histologic grade and type of small papillary renal cell carcinomas (pRCCs) using texture analysis and machine learning algorithms.

METHODS

This was a retrospective HIPAA-compliant study. 24 noncontrast (NC), 22 corticomedullary (CM) phase, and 24 nephrographic (NG) phase CTs of small (< 4 cm) surgically resected pRCCs were identified. Surgical pathology classified the tumors as low- or high-Fuhrman histologic grade and type 1 or 2. The axial image with the largest cross-sectional tumor area was exported and segmented. Six histogram and 31 texture (20 gray-level co-occurrences and 11 gray-level run-lengths) features were calculated for each tumor in each phase. Feature values in low- versus high-grade and type 1 versus 2 pRCCs were compared. Area under the receiver operating curve (AUC) was calculated for each feature to assess prediction of histologic grade and type of pRCCs in each phase. Histogram, texture, and combined histogram and texture feature sets were used to train and test three classification algorithms (support vector machine (SVM), random forest, and histogram-based gradient boosting decision tree (HGBDT)) with stratified shuffle splits and threefold cross-validation; AUCs were calculated for each algorithm in each phase to assess prediction of histologic grade and type of pRCCs.

RESULTS

Individual histogram and texture features did not have statistically significant differences between low- and high-grade or type 1 and type 2 pRCCs across all phases. Individual features had low predictive power for tumor grade or type in all phases (AUC < 0.70). HGBDT was highly accurate at predicting pRCC histologic grade and type using histogram, texture or combined histogram and texture feature data from the CM phase (AUCs = 0.97-1.0). All algorithms had highest AUCs using CM phase feature data sets; AUCs decreased using feature sets from NC or NG phases.

CONCLUSIONS

The histologic grade and type of small pRCCs can be predicted with classification algorithms using CM histogram and texture features, which outperform NC and NG phase image data. The accurate prediction of pRCC histologic grade and type may be able to further guide management of patients with small (< 4 cm) pRCCs being considered for active surveillance.

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.

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

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

Papillary Renal Cell Carcinoma in Lynch/Muir-Torre Syndrome with Germline Pathogenic Variant in MSH6 and Molecular Analysis: Report of a Case and Review of the Literature

Lynch syndrome (LS) is an autosomal dominant inherited disorder due to pathogenic variations in the mismatch repair genes, which predisposes to malignancies, most commonly colon and endometrial carcinoma. Muir-Torre syndrome is a subset of LS with cutaneous sebaceous adenoma and keratoacanthoma in addition to the malignancies. Renal cell carcinoma (RCC) in patients with LS is extremely rare. Only 26 cases have been reported and among them, only two cases of papillary RCC. We report a case of synchronous papillary RCC and colonic adenocarcinoma in an 85-year-old male with Lynch/Muir-Torre syndrome. The LS was diagnosed when he presented with multiple sebaceous adenomas and genetic testing showed a pathogenic variant in MSH6 mismatch repair gene. A colonoscopy at that time showed multiple tubular adenomas with high-grade dysplasia. He was lost to follow-up and presented with gastrointestinal bleeding after 20 years. A right colonic mass, and a solid mass in the lower pole of the right kidney, was detected by imaging. Right Colectomy showed a T3N0 mucin-producing adenocarcinoma. Right nephrectomy showed a T3a papillary RCC which was microsatellite stable with MSH6, and KRAS mutation. The 36-month follow-up exams showed additional sebaceous neoplasms, and an absence of metastatic carcinoma. Analysis of the reported cases of RCC in LS show clear cell RCC as the most common type. These tumors showed MLH1 mutation most commonly, unlike the urothelial malignancies in LS which involve MSH2. Among the 4 cases of RCC with MSH6 mutation, three were in females, indicating some gender differences.

Clinicopathological and molecular characterisation of papillary renal neoplasm with reverse polarity and its renal papillary adenoma analogue

AIMS

Papillary renal neoplasm with reverse polarity (PRNRP) is a newly defined entity with distinct histomorphology and recurrent KRAS mutation. It has been estimated to constitute 4% of previously diagnosed papillary renal cell carcinoma (PRCC). Renal papillary adenoma (PA) is suggested to be the precursor of PRCC. This study aimed to investigate the association between PRNRP and PA, particularly the morphologically similar type D PA.

METHODS AND RESULTS

Nephrectomy specimens of PRCC and PA from our 10-year pathology archives were retrieved and reviewed. GATA3 immunohistochemistry and RAS/BRAF testing were performed in all cases reclassified as PRNRP and all PAs with sufficient materials. Overall, PRNRP accounted for 9.1% (10 of 110) of PRCC and there was no recurrence/metastasis with a mean follow-up period of 39 months. Three novel morphological features were described, including clear cell change, mast cell infiltration and metaplastic ossification. Nine of the 10 PRNRPs showed diffuse and strong GATA3 expression and KRAS missense mutations at codon 12. One case exhibited moderate GATA3 staining on 80% of the tumour cells and RAS/BRAF wild-type. In a total of 73 PAs, 11 were classified as type D. GATA3 expression was significantly more frequent in type D versus non-type D PAs (100 versus 35%, P < 0.01). KRAS missense mutations were identified in six of eight (75%) of the type D PAs but none of the 18 non-type D PAs.

CONCLUSIONS

Type D PA was different from other types of PA and represented an analogue or a small-sized PRNRP for their identical morphology, immunophenotype and molecular signature.

Morphological, immunohistochemical, and genomic analyses of papillary renal neoplasm with reverse polarity

Papillary renal neoplasm with reverse polarity (PRNRP) is a recently proposed entity of renal tumor. It shows a far better prognosis than papillary renal cell carcinoma (PRCC) and frequently has KRAS missense mutation. In this study, we compared 14 cases of PRNRP and 10 cases of PRCC type 1 (PRCC1) and type 2 (PRCC2) from clinical, morphological, immunohistochemical, and molecular biological perspectives. We subjected all PRNRP and PRCC cases to immunohistochemical analysis. Whole-exome sequencing using next-generation sequencing (NGS) was performed for six cases of PRNRP, three cases of PRCC1, and four cases of PRCC2. A search for KRAS gene mutation in the remaining eight cases of PRNRP was performed by polymerase chain reaction (PCR) sequencing. The results showed that all cases of PRNRP were pT1N0M0, none of which followed a course of recurrence or tumor-related death. Immunohistochemical analysis revealed diffuse staining of CK7, EMA, PAX8, and GATA3 but weak or negative staining of CD10, CD15, and AMACR in PRNRP. By NGS and PCR, KRAS missense mutation was detected in 11 of 14 PRNRP cases, although pathogenic KRAS mutation was not observed in PRCC1 and PRCC2. NGS analysis revealed less tumor mutation burden in PRNRP than in PRCC. PRNRP also showed no specific chromosomal copy number abnormalities, including gains of 7 and 17. In conclusion, we propose that PRNRP is a distinct condition from PRCC.

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.

High WHO/ISUP Grade and Unfavorable Architecture, Rather Than Typing of Papillary Renal Cell Carcinoma, May Be Associated With Worse Prognosis

Conflicting data have been published on the prognostic significance of histologic parameters in papillary renal cell carcinoma (PRCC). We conducted a comprehensive evaluation of clinical and histologic parameters in PRCC in nephrectomies and their impact on prognosis, with an emphasis on World Health Organization (WHO)/International Society of Urological Pathology (ISUP) grade, tumor architecture (solid, micropapillary, and hobnail), and PRCC type. A total of 185 PRCC cases were evaluated, 117 (63.2%) type 1, 45 (24.3%) type 2, and 11 (5.9%) mixed type 1 and type 2. Using WHO/ISUP grading criteria, PRCCs were graded as follows: 6 (3.2%) grade 1; 116 (62.7%) grade 2; 61 (33.0%) grade 3; and 2 (1.1%) grade 4. The solid architecture was present in 3 cases (1.6%) and comprised 10%, 10%, and 30% of the tumor area. Micropapillary architecture was present in 10 cases (5.4%), ranging from 5% to 30% of the tumor (mean=11%; median=10%). Hobnail architecture was seen in 9 cases (4.9%), with mean percentage of 23% (median=15%; range: 5% to 50%) involvement of tumor area. Parameters associated with worse disease-free survival (DFS) and overall survival (OS) in the univariate analysis included WHO/ISUP grade, pathologic stage, tumor size, and solid, micropapillary, or hobnail architecture (P<0.05). The pathologic stage and WHO/ISUP grade were significantly associated with both DFS and OS in stepwise multivariate Cox regression analysis (P<0.05). In addition, micropapillary architecture and type 1 histology were linked with an adverse impact on OS (P<0.05). We found no difference in DFS (P=0.8237) and OS (P=0.8222) for type 1 versus type 2 PRCC in our patient cohort. In addition, we performed a meta-analysis with data from studies with reported hazard ratios (HRs) on PRCC type in relation to DFS and OS. We identified 5 studies that reported DFS and found no significant effect for type 2 PRCC (P=0.30; HR=1.43; 95% confidence interval: 0.73-2.80). We identified 7 studies that reported OS and found no significant association between type 2 PRCC and worse OS (P=0.41; HR: 1.21; 95% confidence interval: 0.77-1.91). Our findings suggest that high WHO/ISUP grade and unfavorable architecture (solid, micropapillary, or hobnail), rather than typing of PRCC, are associated with worse outcomes.

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.

Management of Metastatic Nonclear Renal Cell Carcinoma: What Are the Options and Challenges?

This case presents a 68-yr-old female patient with primary metastatic nonclear renal cell carcinoma (RCC) with multiple bone lesions. The patient underwent a single resection of skull bone lesion (diagnostic for poorly differentiated carcinoma of unknown origin) and cytoreductive nephrectomy. The pathology of the kidney specimen demonstrated an oncocytic papillary RCC. Within 3 mo, she developed skeletal progressive disease and was started on systemic therapy (sunitinib). After initial stabilization, bone metastasis progressed during the third cycle of sunitinib and required second-line therapy (cabozantinib). One of the major unmet needs in non-clear cell RCC is the lack of specific systemic therapy. Data on immunotherapy are still limited. Inclusion of these patients in clinical trials is strongly recommended. PATIENT SUMMARY: Patients with metastatic kidney cancer who present with the less common histological subtype (non-clear cell) have poor survival. In this case, the patient responded to second-line therapy. Very few therapies provide response to treatment. Patients should be offered participation in clinical trials testing combinations with immunotherapy.

Recurrent KRAS mutations in papillary renal neoplasm with reverse polarity

We recently proposed that an epithelial renal tumor "papillary renal neoplasm with reverse polarity" represents a distinct entity. It constituted 4% of previously diagnosed papillary renal cell carcinoma at the participating institutions. Histologically, it is characterized by papillary or tubulopapillary architecture covered by a single layer of eosinophilic cells with finely granular cytoplasm and apically located nuclei. It is characteristically positive for GATA3 and L1CAM and lack vimentin and, to a lesser extent, α-methylacyl-CoA-racemase (AMACR/p504s) immunostaining. To investigate the molecular pathogenesis of these tumors, we performed targeted next-generation sequencing on ten previously reported papillary renal neoplasms with reverse polarity, followed by a targeted polymerase chain reaction analysis for KRAS mutations in a control series of 30 type 1 and 2 papillary renal cell carcinomas. KRAS missense mutations were identified in eight of ten papillary renal neoplasms with reverse polarity. These mutations were clustered in exon 2-codon 12: c.35 G > T (n = 6) or c.34 G > C (n = 2) resulting in p.Gly12Val and p.Gly12Arg alterations, respectively. One of the wild-type tumors had BRAF c.1798_1799delGTinsAG (p.Val600Arg) mutation. No KRAS mutations were identified in any of the 30 control tumors. In summary, this study supports our proposal that papillary renal neoplasm with reverse polarity is an entity distinct from papillary renal cell carcinoma and the only renal cell neoplasm to consistently harbor KRAS mutations.

Identification of miR-21-5p and miR-210-3p serum levels as biomarkers for patients with papillary renal cell carcinoma: a multicenter analysis

Background

Expression of circulating serum microRNAs has not been studied in a cohort of patients with papillary renal cell carcinoma (pRCC) so far. We hypothesized that miRNA deregulation in malignant tissue is reflected in serum and could be used for non-invasive diagnosis of pRCC as well as differentiation between type 1 and type 2 pRCC.

Methods

We selected 11 differentially regulated miRNAs from the Cancer Genome Atlas (TCGA) pRCC data set as potential serum validation candidates. Serum miRNA expression was determined by qRT-PCR in a total of 34 pRCC type 1, 33 pRCC type 2 and 33 control subjects of three german high-volume medical centers.

Results

Heatmap and principal component analysis showed that miRNA expression did not cluster the samples into distinct sample groups and that miRNA levels did not significantly discriminate healthy individuals from patients with pRCC, nor between patients with type 1 and type 2 pRCC. However, miR-21-5p levels were significantly increased in patients with advanced pRCC (>pT3, and/or pN+ and/or pM+) in comparison to localized pRCC. Moreover, adding the expression of miR-210-3p, which was significantly down-regulated in localized pRCC sera in comparison to healthy sera, additionally increased diagnostic accuracy in our study cohort.

Conclusions

In our multicenter cohort, we were not able to identify a single miRNA serum marker for pRCC including its subclasses. However, our study revealed that miR-21-5p levels were elevated in advanced disease (with added diagnostic accuracy via addition of miR-210-3p expression), proposing these two miRs as potential biomarkers in pRCC.

Frequent KRAS mutations in oncocytic papillary renal neoplasm with inverted nuclei

AIMS

Papillary renal neoplasm with reverse polarity (PRNRP) is a newly documented rare tumour type. Its molecular pathological features have thus far been very little studied.

METHODS AND RESULTS

There were 13 PRNRP cases including 3 The Cancer Genome Atlas (TCGA) cases and our 10 cases in this study. The 3 TCGA cases were found by a combined analysis of GATA3 mRNA expression levels and digital slides from the TCGA papillary renal cell carcinoma project. KRAS codon 12 mutations were identified in the three PRNRPs from TCGA. Of our 10 PRNRP cases, the mutations were also discovered using Sanger sequencing in seven (77.8%) of nine cases with available DNA, where KRAS p.G12V (n = 3), p.G12D (n = 2), p.G12R (n = 1) and p.G12C (n = 1) alterations were found. PRNRP shared similar gene expression profiles with renal distal tubules via an interprofile correlation analysis. Gene set enrichment analysis revealed that genes involved in 'KEGG aldosterone regulated sodium reabsorption' or 'hallmark apical surface' were enriched in PRNRP. Moreover, polarised immunostaining patterns for L1CAM and EMA in the distal tubule were maintained in PRNRP.

CONCLUSIONS

These results imply that the tumour potentially originates from the distal tubule, especially from the cortical collecting duct, and probably retains its cell polarity, except for nuclear inversion. We therefore propose that oncocytic papillary renal neoplasm with inverted nuclei (OPRNIN) is a better name for this tumour type. OPRNIN is a kidney site-specific KRAS mutation neoplasm different from conventional papillary renal cell carcinoma.

Papillary Renal Neoplasm With Reverse Polarity: A Clinicopathologic Study of 7 Cases

Papillary renal neoplasm with reverse polarity is a form of recently described tumor. These tumors are defined by GATA3 positivity, negative vimentin staining, and the presence of both papillary structures and a layer of eosinophilic cells with apical nuclei and a granular cytoplasm. In the present report, we review 7 cases of papillary renal neoplasm with reverse polarity that were GATA3+ and vimentin-, consistent with past reports. In all 7 of these cases, we found that these tumors were additionally positive for 34βE12. All 7 of these tumors were categorized as stage pT1. On histological examination, these tumors exhibited branching papillae with apical nuclei. All 7 of these patients were alive on most recent follow-up, with 6 being disease free and one having developed prostate cancer. Together, this overview of 7 additional cases of papillary renal neoplasm with reverse polarity offers further insight into this rare and poorly understood disease.

Recurrent KRAS mutations identified in papillary renal neoplasm with reverse polarity-a comparative study with papillary renal cell carcinoma

Comprehensive molecular analyses revealed that papillary renal cell carcinoma (PRCC) is a heterogenous entity. Papillary renal neoplasm with reverse polarity (PRNRP) is a subset of PRCC with characteristic histomorphologies such as low-grade nuclear features, inverted nuclear location, eosinophilic cytoplasm, and indolent clinical behavior. We tried to define the molecular, clinicopathological, histologic, and immunohistochemical features of PRNRP by comparing them with type 1 PRCC (PRCC1) and type 2 PRCC (PRCC2). A cohort of 30 PRNRP, 23 PRCC1, and 26 PRCC2 cases was used. Targeted sequencing of 90 cancer-related genes including KRAS was performed in 26 PRNRP tumor samples. PNA-mediated clamping PCR of KRAS was performed using paired normal and tumor DNA from 30 PRNRP, 23 PRCC1, and 26 PRCC2 cases. Tissue microarray slides were made in three cores per tumor, which were stained with cytokeratin 7 (CK7), alpha-methylacyl-CoA racemase (AMACR), epithelial membrane antigen (EMA), E-cadherin, vimentin, and CD10. Recurrent mutations in KRAS were detected in 28 of the 30 PRNRPs. However, there were no KRAS mutations in any PRCC1 or PRCC2 cases. PRNRP exhibited distinct clinicopathological features: small tumor size, lower pathologic T stage, and no disease-specific death during the follow-up period. Histologically, peritumoral lymphoid aggregation, prominent papillary architecture (>80% of tumor), hyalinized papillae, inverted nuclear location, and lower nuclear grade were observed. PRNRP was usually positive for CK7, AMACR, EMA, and E-cadherin, and negative for CD10. The findings suggest that PRNRP is a subtype of papillary renal neoplasm that is different from PRCC1 or PRCC2 in terms of molecular, clinicopathological, histological, and immunohistochemical features.

Papillary Renal Neoplasm With Reverse Polarity: A Morphologic, Immunohistochemical, and Molecular Study

We evaluated the clinicopathologic and chromosomal characteristics of a distinct subset of papillary renal tumors and compared them to a control series of papillary renal cell carcinoma types 1 and 2. Of the 18 patients, 9 were women and 9 were men, ranging in age from 46 to 80 years (mean, 64 y; median, 66 y). The tumors ranged in diameter from 0.6 to 3 cm (mean, 1.63 cm; median, 1.4 cm). Fourteen tumors were WHO/ISUP grade 2 and 4 were grade 1. All were stage category pT1. The tumors had branching papillae with thin fibrovascular cores, covered by cuboidal to columnar cells with granular eosinophilic cytoplasm, smooth luminal borders, and mostly regular and apically located nuclei with occasional nuclear clearing and inconspicuous nucleoli. Tubule formation and clear cytoplasmic vacuoles were observed in 5 and 9 tumors, respectively. Ten tumors had pseudocapsules. Psammoma bodies, necrosis, mitotic figures and intracellular hemosiderin are absent from all tumors. In contrast, papillary renal cell carcinoma type 1 consisted of delicate papillae covered by a single layer of cells with scanty pale cytoplasm with nuclei generally located in a single layer on the basement membrane of the papillary cores, while type 2 tumors had broad papillae covered by pseudostratified cells with eosinophilic cytoplasm and more randomly located nuclei. Both had occasional psammoma bodies, foamy macrophages and intracellular hemosiderin. Immunohistochemically, all were positive for pancytokeratin AE1/AE3, epithelial membrane antigen, MUC1, CD10, GATA3, and L1CAM. Cytokeratin 7 was positive in 16 tumors (1 had <5% positivity). CD117 and vimentin were always negative. α-methylacyl-CoA-racemase (AMACR/p504s) showed variable staining (range, 10% to 80%) in 5 tumors. However, all tumors in the control group were negative for GATA3 and positive for AMACR/p504s and vimentin immunostains. Fluorescence in situ hybridization analysis of the study group demonstrated chromosome 7 trisomy in 5 tumors (33%), trisomy 17 in 5 tumors (33%), and trisomy 7 and 17 in 3 tumors (20%). Chromosome Y deletion was found in 1 of 7 male patients and chromosome 3p was present in all tumors. No tumor recurrence or metastasis occurred. In summary, we propose the term papillary renal neoplasm with reverse polarity for this entity.

Knowledge Translation in Oncology: The Bumpy Ride From Bench to Bedside

OBJECTIVES

Knowledge translation (KT) is the dynamic process of mobilizing best-practice evidence to guide health care decisions.

METHODS

Using a PubMed search, challenges were identified and milestones defined.

RESULTS

Substantial challenges exist in integrating discoveries into patient care, including technical limitations related to genomic testing like turnaround time, standardization, reproducibility, and results interpretation. Other challenges include lack of proper training in genetic counseling for health care providers, clarity of scientific evidence, and ethical, legal and social considerations. In addition, most health care systems lack accessibility to genetic testing services. Moving forward, KT should be addressed at three main frontiers. The first is patients centered for proper understanding and decision making; the second is directed toward health care professionals, including clinical decision support and clarity of roles; and the third addresses resources of health care systems.

CONCLUSIONS

Implementing KT requires developing strategies to enhance awareness and promote behavioral changes congruent with research evidence, designing a systematic approach by health care providers and stakeholders to achieve patient-centered care.

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.