Morphologic typing of papillary renal cell carcinoma: comparison of growth kinetics and patient survival in 66 cases

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.

The prognostic role of histomorphological subtyping in nonmetastatic papillary renal cell carcinoma after curative surgery: is subtype really irrelevant? A propensity score matching analysis of a multi-institutional real life data

BACKGROUND AND AIM

The role of histomorphological subtyping is an issue of debate in papillary renal cell carcinoma (papRCC). This multi-institutional study investigated the prognostic role of histomorphological subtyping in patients undergoing curative surgery for nonmetastatic papRCC.

PATIENTS AND METHODS

A total of 1,086 patients undergoing curative surgery were included from a retrospectively collected multi-institutional nonmetastatic papRCC database. The patients were divided into 2 groups based on histomorphological subtyping (type 1, n = 669 and type 2, n = 417). Furthermore, a propensity score-matching (PSM) cohort in 1:1 ratio (n = 317 for each subtype) was created to reduce the effect of potential confounding variables. The primary outcome of the study, the predictive role of histomorphological subtyping on the prognosis (recurrence free survival [RFS], cancer specific survival [CSS] and overall survival [OS]) in nonmetastatic papRCC after curative surgery, was investigated in both overall and PSM cohorts.

RESULTS

In overall cohort, type 2 group were older (66 vs. 63 years, P = 0.015) and more frequently underwent radical nephrectomy (37.4% vs. 25.6%, P < 0.001) and lymphadenectomy (22.3% vs. 15.1%, P = 0.003). Tumor size (4.5 vs. 3.8 cm, P < 0.001) was greater, and nuclear grade (P < 0.001), pT stage (P < 0.001), pN stage (P < 0.001), VENUSS score (P < 0.001) and VENUSS high risk (P < 0.001) were significantly higher in type 2 group. 5-year RFS (89.6% vs. 74.2%, P < 0.001), CSS (93.9% vs. 84.2%, P < 0.001) and OS (88.5% vs. 78.5%, P < 0.001) were significantly lower in type 2 group. On multivariable analyses, type 2 was a significant predictor for RFS (HR:1.86 [95%CI:1.33-2.61], P < 0.001) and CSS (HR:1.91 [95%CI:1.20-3.04], P = 0.006), but not for OS (HR:1.27 [95%CI:0.92-1.76], P = 0.150). In PSM cohort balanced with age, gender, symptoms at diagnosis, pT and pN stages, tumor grade, surgical margin status, sarcomatoid features, rhabdoid features, and presence of necrosis, type 2 increased recurrence risk (HR:1.75 [95%CI: 1.16-2.65]; P = 0.008), but not cancer specific mortality (HR: 1.57 [95%CI: 0.91-2.68]; P = 0.102) and overall mortality (HR: 1.01 [95%CI: 0.68-1.48]; P = 0.981) CONCLUSIONS: This multiinstitutional study suggested that type 2 was associated with adverse histopathologic outcomes, and predictor of RFS and CSS after surgical treatment of nonmetastatic papRCC, in overall cohort. In propensity score-matching cohort, type 2 remained the predictor of RFS. Eventhough 5th WHO classification for renal tumors eliminated histomorphological subtyping, these findings suggest that subtyping is relevant from the point of prognostic view.

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.

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.

The utilization of single-cell sequencing technology in investigating the immune microenvironment of ccRCC

The growth and advancement of ccRCC are strongly associated with the presence of immune infiltration and the tumor microenvironment, comprising tumor cells, immune cells, stromal cells, vascular cells, myeloid-derived cells, and extracellular matrix (ECM). Nevertheless, as a result of the diverse and constantly evolving characteristics of the tumor microenvironment, prior advanced sequencing methods have frequently disregarded specific less prevalent cellular traits at varying intervals, thereby concealing their significance. The advancement and widespread use of single-cell sequencing technology enable us to comprehend the source of individual tumor cells and the characteristics of a greater number of individual cells. This, in turn, minimizes the impact of intercellular heterogeneity and temporal heterogeneity of the same cell on experimental outcomes. This review examines the attributes of the tumor microenvironment in ccRCC and provides an overview of the progress made in single-cell sequencing technology and its particular uses in the current focus of immune infiltration in ccRCC.

Oncological outcomes of papillary versus clear cell renal cell carcinoma in pT1 and pT2 stage: Results from a contemporary Turkish patient cohort

OBJECTIVES

To compare overall survival (OS), recurrence free survival (RFS), and cancer-specific survival (CSS) in the long-term follow-up of T1 and T2 clear-cell-Renal Cell Carcinoma (ccRCC) and papillary Renal Cell Carcinoma (pRCC) patients, as well as to determine the risk factors for recurrence and overall mortality.

MATERIAL AND METHOD

Data of patients with kidney tumors obtained from the Urologic Cancer Database - Kidney (UroCaD-K) of Turkish Urooncology Association (TUOA) were evaluated retrospectively. Out of them, patients who had pathological T1-T2 ccRCC and pRCC were included in the study. According to the two histological subtype, recurrence and mortality status, RFS, OS and CSS data were analyzed.

RESULTS

RFS, OS and CSS of pRCC and ccRCC were found to be similar. Radiological local invasion was shown to be a risk factor for recurrence in pRCC, and age was the only independent factor affecting overall mortality.

CONCLUSIONS

There were no differences in survivals (RFS, OS and CSS) of patients with localized papillary and clear cell RCC. While age was the only factor affecting overall mortality, radiological local invasion was a risk factor for recurrence in papillary RCC.

Identification of prognostic and therapeutic biomarkers in type 2 papillary renal cell carcinoma

BACKGROUND

Papillary renal cell carcinoma (PRCC) can be divided into type 1 (PRCC1) and type 2 (PRCC2) and PRCC2 share a more invasive phenotype and worse prognosis. This study aims to identify potential prognostic and therapeutic biomarkers in PRCC2.

METHODS

A cohort from The Cancer Genome Atlas and two datasets from Gene Expression Omnibus were examined. Common differentially expressed genes (DEGs) were screened and potential biomarkers were explored by using Kaplan-Meier method and cox regression analysis. Functional enrichment analysis was utilized to evaluate the potential biological functions. Tumor infiltrating immune cells were estimated by CIBERSORT algorithm. Ninety-two PRCC2 samples from Fudan University Shanghai Cancer Center were obtained, and immunostaining was performed to validate prognostic and therapeutic significance of the potential biomarker.

RESULTS

PRCC2 has worse overall survival and shares distinct molecular characteristics from PRCC1. There was significant higher expression level of Targeting protein for Xklp2 (TPX2) in PRCC2 compared with normal tissues. Higher expression level of TPX2 was significantly associated with worse overall survival in PRCC2 and kinesin family genes expression were found significantly elevated in high risk PRCC2. Abundance of tumor infiltrating M1 macrophage was significantly higher in PRCC2 and it was also associated with worse overall survival. In the FUSCC cohort, higher TPX2 expression was significantly correlated with worse overall and progression-free survival. Retrospective analysis indicated that mTOR inhibitor (everolimus) had greater efficacy in the high-risk group than in the low-risk group (overall response rate: 28.6% vs. 16.7%) and that everolimus had greater efficacy than sunitinib in the high-risk group (overall response rate: 28.6% vs. 20%).

CONCLUSIONS

TPX2 was a prognostic and therapeutic biomarker in PRCC2. Higher abundance of tumor infiltrating M1 macrophage was significantly associated with worse overall survival in PRCC2. mTOR inhibitors may have good efficacy in patients with high-risk PRCC2.

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.

Identification of prognostic biomarkers in papillary renal cell carcinoma and PTTG1 may serve as a biomarker for predicting immunotherapy response

OBJECTIVE

This study aims to identify potential prognostic and therapeutic biomarkers in papillary renal cell carcinoma (pRCC).

METHODS

Two microarray datasets were downloaded from the Gene Expression Omnibus (GEO) database and differentially expressed genes (DEGs) were identified. The protein-protein interaction (PPI) networks and functional annotations of DEGs were established. Survival analysis was utilized to evaluate the prognostic significance of the DEGs and the association between the expression level of candidate biomarkers and various tumour-infiltrating immune cells was explored. The role of PTTG1 in tumour microenvironments (TME) was further explored using Single-cell RNA-seq and its prognostic and therapeutic significance was validated in Fudan University Shanghai Cancer Centre (FUSCC) cohort.

RESULTS

Eight genes, including BUB1B, CCNB1, CCNB2, MAD2L1, TTK, CDC20, PTTG1, and MCM were found to be negatively associated with patients' prognosis. The expression level of PTTG1 was found to be significantly associated with lymphocytes, immunomodulators, and chemokine in the TCGA cohort. Single-cell RNA-seq information indicated that PTTG1 was strongly associated with the proliferation of T cells. In the FUSCC cohort, the expression level of PTTG1 was also statistically significant for both progression-free survival (PFS) and overall survival (OS) prediction (HR = 2.683, p < .001; HR = 2.673, p = .001). And higher expression level of PTTG1 was significantly associated with immune checkpoint blockade (ICB) response in the FUSCC cohort (χ²=3.99, p < .05).

CONCLUSIONS

Eight genes were identified as a prognostic biomarker and the expression level of PTTG1 was also found to serve as a potential predictor for ICB response in pRCC patients.Key messages:Eight genes, including BUB1B, CCNB1, CCNB2, MAD2L1, TTK, CDC20, PTTG1, and MCM were found to be negatively associated with pRCC patients' prognosis.Expression level of PTTG1 was significantly associated with tumour microenvironment including lymphocytes, immunomodulators, and chemokines.Higher expression level of PTTG1 was significantly associated with immune checkpoint blockade (ICB) response in FUSCC cohort.

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.

Immunohistochemical Expression of CD44, MMP-2, MMP-9, and Ki-67 as the Prognostic Markers in Non-Clear Cell Renal Cell Carcinomas-A Prospective Cohort Study

CD44 is the most frequently reported marker of the cancer stem cells in renal cell carcinoma (RCC). Matrix metalloproteinases MMP-2 and MMP-9 are key regulators of tumor invasion and metastasis. The aim of this study was to investigate the clinicopathologic and prognostic values of the immunohistochemical expression of CD44, MMP2, MMP9, and Ki-67 in papillary and chromophobe RCCs. In the case of papillary RCC, MMP-2 expression was positively correlated with patient age (p < 0.05), while CD44 expression was positively correlated with tumor stage (τ = 0.26, p < 0.05). Moreover, CD44 expression positively correlated with MMP-9 (τ = 0.39, p < 0.05). In the case of chromophobe RCC, only Ki-67 expression was negatively correlated with tumor stage (τ = −0.44, p < 0.05). During follow-up, a death was documented in 6 patients with papillary RCC. In these patients, CD44 expression was not a significant factor affecting the overall survival of patients (p > 0.05), whereas there was a positive correlation between increased MMP-9 expression and shorter overall survival (p < 0.05). Taken together, carcinogenesis in papillary RCC is probably dependent on both cancer stem cells and metalloproteinases activity. Expression of CD44 and MMP-9 can significantly improve the prediction of papillary RCC prognosis in the future.

Identification of an immune-related gene prognostic index for predicting survival and immunotherapy efficacy in papillary renal cell carcinoma

Despite considerable progress has been made in the understanding of the genetics and molecular biology of renal cell carcinoma (RCC), therapeutic options of patients with papillary renal cell carcinoma (PRCC) are limited. Immunotherapy based on immune checkpoint inhibitors (ICIs) has become a hot point in researching new drug for tumor and been tested in a number of human clinical trials. In this study, an immune-related gene prognostic index (IRGPI) was developed and provided a comprehensive and systematic analysis of distinct phenotypic and molecular portraits in the recognition, surveillance, and prognosis of PRCC. The reliability of the IRGPI was evaluated using independent datasets from GEO database and the expression levels of the genes in the IRGPI detected by real-time PCR. Collectively, the currently established IRGPI could be used as a potential biomarker to evaluate the response and efficacy of immunotherapy in PRCC.

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.

The Prognostic Impact of PD-L2 in Papillary Renal-Cell Carcinoma

INTRODUCTION

Programmed death-1 ligand (PD-L1) has been often studied in different types of renal-cell carcinoma (RCC). For example, in clear-cell renal carcinoma it is well established that programmed death-1 receptor and PD-L1 are important prognostic markers. In contrast, the role of programmed death-2 ligand (PD-L2) as prognostic marker remains unclear. The aim of this study was to evaluate if PD-L2 expression could play a role as a prognostic marker for papillary RCC (pRCC).

METHODS

The patients' sample collection was a joint collaboration of the PANZAR consortium. Patients' medical history and tumor specimens were collected from n = 240 and n = 128 patients with type 1 and 2 pRCC, respectively. Expression of PD-L2 was determined by immunohistochemistry. In total, PD-L2 staining was evaluable in 185 of 240 type 1 and 99 of 128 type 2 pRCC cases.

RESULTS

PD-L2 staining was positive in 67 (36.2%) of type 1 and in 31 (31.3%) of type 2 pRCC specimens. The prevalence of PD-L2+ cells was significantly higher in high-grade type 1 tumors (p = 0.019) and in type 2 patients with metastasis (p = 0.002). Kaplan-Meier analysis disclosed significant differences in 5-year overall survival (OS) for patients with PD-L2- compared to PD-L2+ in pRCC type 1 of 88.4% compared to 73.6% (p = 0.039) and type 2 of 78.8% compared to 39.1% % (p < 0.001). However, multivariate analysis did not identify the presence of PD-L2+ cells neither in type 1 nor type 2 pRCC as an independent predictor of poor OS.

DISCUSSION/CONCLUSION

PD-L2 expression did not qualify as an independent prognostic marker in pRCC. Future studies will have to determine whether anti-PD-L2-targeted treatment may play a role in pRCC and expression can potentially serve as a predictive marker for these therapeutic approaches.

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.

Long Non-Coding RNAs as Novel Biomarkers in the Clinical Management of Papillary Renal Cell Carcinoma Patients: A Promise or a Pledge?

Papillary renal cell carcinoma (pRCC) represents the second most common subtype of renal cell carcinoma, following clear cell carcinoma and accounting for 10-15% of cases. For around 20 years, pRCCs have been classified according to their mere histopathologic appearance, unsupported by genetic and molecular evidence, with an unmet need for clinically relevant classification. Moreover, patients with non-clear cell renal cell carcinomas have been seldom included in large clinical trials; therefore, the therapeutic landscape is less defined than in the clear cell subtype. However, in the last decades, the evolving comprehension of pRCC molecular features has led to a growing use of target therapy and to better oncological outcomes. Nonetheless, a reliable molecular biomarker able to detect the aggressiveness of pRCC is not yet available in clinical practice. As a result, the pRCC correct prognosis remains cumbersome, and new biomarkers able to stratify patients upon risk of recurrence are strongly needed. Non-coding RNAs (ncRNAs) are functional elements which play critical roles in gene expression, at the epigenetic, transcriptional, and post-transcriptional levels. In the last decade, ncRNAs have gained importance as possible biomarkers for several types of diseases, especially in the cancer universe. In this review, we analyzed the role of long non-coding RNAs (lncRNAs) in the prognosis of pRCC, with a particular focus on their networking. In fact, in the competing endogenous RNA hypothesis, lncRNAs can bind miRNAs, resulting in the modulation of the mRNA levels targeted by the sponged miRNA, leading to additional regulation of the target gene expression and increasing complexity in the biological processes.

Clinicopathological Features of Papillary Renal Cell Carcinoma With Venous Tumor Thrombus: Case Series from a Large Chinese Center

Background:

Few studies have reported the influence of the histological classification of type-2 papillary renal cell carcinoma (PRCC), which may differ from that of clear cell renal carcinoma (ccRCC), on the prognosis of renal cell carcinoma with tumor thrombus. We investigated the clinicopathological features and prognosis of type-2 PRCC associated with venous tumor thrombi (PRCC-TT).

Methods:

We retrospectively analyzed 163 patients with renal cell carcinoma with venous tumor thrombus (RCC-TT) admitted to Peking University Third Hospital between June 2016 and June 2020. Twenty-five patients had type-2 PRCC-TT and 138 had ccRCC combined with tumor thrombus; there were 125 males and 38 females. All the included patients underwent radical nephrectomy and thrombectomy under either complete laparoscopic surgery or open surgery. Univariate and multivariate Cox regression analysis were performed to evaluate the prognostic significance of each variable on cancer-specific survival (CSS). Cancer-specific survival was calculated from the date of surgery to death or the last follow-up using the Kaplan–Meier method.

Results:

The blood vessels of type-2 PRCC-TT presented on CT images were not as abundant as those of ccRCC-TT. Slight enhancement was observed in the corticomedullary phase. While wash-out symptoms were observed, contrast agent extinction was not obvious in the nephrographic and excretory phases. We compared the macroscopic and microscopic appearances of the 2 cohorts. Compared to the ccRCC-TT cohort, lymph node invasion was more prevalent in the PRCC-TT cohort (88.0% vs. 60.9%, P = .009). Multivariate analysis revealed that sarcomatoid differentiation, distant metastasis, and pathological type were the independent predictors of poor CSS. The Kaplan–Meier analysis showed that the CSS of type-2 PRCC-TT and ccRCC-TT were 23.5 and 38.4 months, respectively, with statistical significance (P = .002).

Conclusion:

Type-2 PRCC-TT varies with common ccRCC-TT in imaging manifestation and pathological characteristics. The prognosis of type-2 PRCC-TT patients was worse than that of ccRCC-TT patients.

Association between preoperative serum Cystatin-C levels and postsurgical oncological prognosis in patients with PRCC: A retrospective cohort study

OBJECTIVE

Cystatin-C (Cys-C) is a predictor of several malignancies. However, whether Cys-C levels predict prognosis in patients with papillary renal cell carcinoma (PRCC) remains uncertain. The aim of this study was to assess the correlation between Cys-C and clinical outcomes in patients with PRCC.

METHODS

The medical records of 137 patients with PRCC who underwent surgery at our institution from January 2008 to December 2020 were retrospectively analyzed. Data were divided into two subgroups based on cutoff values and the relationship between the Cys-C group and their clinical outcomes was assessed.

RESULTS

By the last follow-up, 62 patients had died of various causes, 53 of whom died from PRCC. Sixty patients suffered recurrence or metastasis during follow-up. Based on the cutoff value, the patients were divided into two groups: low Cys-C group (Cys-C < 1.25 mg/L, n = 92) and high Cys-C group (Cys-C ≥ 1.25 mg/L, n = 45). Pathological classification and serum Cys-C levels were shown to be independent prognostic factors affecting clinical outcomes, according to multivariate Cox regression analysis (p < 0.05). After adjusting the Cox proportional hazards model, the risk of death was elevated in the high Cys-C group. The results of the area under the curve for time-dependent receiver operating characteristics analysis indicated that Cys-C is a stable and reliable prognostic biomarker for predicting survival in patients with PRCC. Forest plots, constructed to better reflect the comparison of hazard ratios between the two groups, confirmed that Cys-C levels were significantly associated with worsening overall survival.

CONCLUSION

This study is the first to examine the relationship between preoperative serum Cys-C levels and prognostic overall survival in patients with PRCC. Cys-C may be a useful biomarker for preoperative screening of high-risk patients who may require adjuvant therapy.

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.

Renal Oncocytoma: The Diagnostic Challenge to Unmask the Double of Renal Cancer

Renal oncocytoma represents the most common type of benign neoplasm that is an increasing concern for urologists, oncologists, and nephrologists due to its difficult differential diagnosis and frequent overtreatment. It displays a variable neoplastic parenchymal and stromal architecture, and the defining cellular element is a large polygonal, granular, eosinophilic, mitochondria-rich cell known as an oncocyte. The real challenge in the oncocytoma treatment algorithm is related to the misdiagnosis due to its resemblance, at an initial radiological assessment, to malignant renal cancers with a completely different prognosis and medical treatment. Unfortunately, percutaneous renal biopsy is not frequently performed due to the possible side effects related to the procedure. Therefore, the majority of oncocytoma are diagnosed after the surgical operation via partial or radical nephrectomy. For this reason, new reliable strategies to solve this issue are needed. In our review, we will discuss the clinical implications of renal oncocytoma in daily clinical practice with a particular focus on the medical diagnosis and treatment and on the potential of novel promising molecular biomarkers such as circulating microRNAs to distinguish between a benign and a malignant lesion.

Clinicopathological Features and Prognostic Outcomes of Papillary Renal Cell Carcinoma

Purpose

Although papillary renal cell carcinoma (pRCC) is the second common renal malignant tumor, the current understanding of pRCC is poor. This study aims to explore the clinicopathological features and prognostic factors of pRCC.

Methods

From August 2007 and August 2017, 87 patients diagnosed with pRCC by postoperative pathology were enrolled. The clinicopathological features between type1 pRCC and type2 pRCC were compared by Chi-square test, Fisher’s exact test, or t-test. The Kaplan–Meier method was performed to estimate progression-free survival (PFS). Univariate and multivariate cox regression models were used to verify the prognostic factors.

Results

Of the 87 cases, the median tumor diameter was 5.3cm. Twenty-nine patients were diagnosed with type1 pRCC and 58 patients with type2 pRCC. According pathological stage, 59 (67.8%) cases were in pT1 stage, 19 (21.8%) in pT2 stage, and 9 (10.4%) in pT3 stage. WHO/ISUP pathological grade revealed that 56 (64.4%) patients were in grade I, 17 (19.5%) in grade II, 7 (8.05%) in grade III, and 7 (8.05%) in grade IV. The median follow-up time was 57.0months, and the 1-, 3-year PFS was 95.4%, and 80.8%, respectively. For type1 and type2 pRCC, 3-years PFS was 93.0% and 74.9%, respectively. Survival of type1 pRCC was better than that of type2 (P= 0.027). Patients with late pT stage, lymph node metastasis, distant metastasis, high pathological grade, and large size exhibited worse survival. pTNM stage, pathological grade, and tumor types were potentially related to prognosis for PFS. However, an independent prognostic factor affecting PFS was not found in multivariate regression models. For patients with the pT1 stage, nephron-sparing surgery (NSS) and radical nephrectomy (RN) did not affect the PFS, ignoring tumor types (P=0.45).

Conclusion

Type2 pRCC is more than type1 pRCC and has an advanced TNM stage and a higher pathological grade. For patients with pRCC with the pT1 stage, the outcome of NSS is not inferior to that of RN.

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.

A construction and comprehensive analysis of ceRNA networks and infiltrating immune cells in papillary renal cell carcinoma

Background

As the second most common malignancy in adults, papillary renal cell carcinoma (PRCC) has shown an increasing trend in both incidence and mortality. Effective treatment for advanced metastatic PRCC is still lacking. In this study, we aimed to establish competitive endogenous RNA (ceRNA) networks related to PRCC tumorigenesis, and analyze the specific role of differentially expressed ceRNA components and infiltrating immune cells in tumorigenesis.

Methods

CeRNA networks were established to identify the key ceRNAs related to PRCC tumorigenesis based on the 318 samples from The Cancer Genome Atlas database (TCGA), including 285 PRCC and 33 normal control samples. The R package, “CIBERSORT,” was used to evaluate the infiltration of 22 types of immune cells. Then we identified the significant ceRNAs and immune cells, based on which two nomograms were obtained for predicting the prognosis in PRCC patients. Finally, we investigated the co‐expression of PRCC‐specific immune cells and core ceRNAs via Pearson correlation test.

Results

COL1A1, H19, ITPKB, LDLR, TCF4, and WNK3 were identified as hub genes in ceRNA networks. Four prognostic‐related tumor‐infiltrating immune cells, including T cells CD4 memory resting, Macrophages M1, and Macrophages M2 were revealed. Pearson correlation test indicated that Macrophage M1 was negatively related with COL1A1 (p < 0.01) and LDLR (p < 0.01), while Macrophage M2 was positively related with COL1A1 (p < 0.01), TCF4 (p < 0.01), and H19 (p = 0.032). Two nomograms were conducted with favorable accuracies (area under curve of 1‐year survival: 0.935 and 0.877; 3‐year survival: 0.849 and 0.841; and 5‐year survival: 0.818 and 0.775, respectively).

Conclusion

The study constructed two nomograms suited for PRCC prognosis predicting. Moreover, we concluded that H19‐miR‐29c‐3p‐COL1A1 axis might promote the polarization of M2 macrophages and inhibit M1 macrophage activation through Wnt signaling pathway, collaborating to promote PRCC tumorigenesis and lead to poor overall survival of PRCC patients.

EWSR1-PATZ1 fusion renal cell carcinoma: a recurrent gene fusion characterizing thyroid-like follicular renal cell carcinoma

Thyroid-like follicular renal cell carcinoma is an uncommon kidney tumor with no distinct molecular alteration described to date. This cohort of eight women with mean and median ages of 45 and 46 years, respectively (range 19-65 years), had unencapsulated, well-circumscribed tumors composed of tightly packed anastomosing follicle-like cysts filled with eosinophilic colloid-like material and lined by cuboidal cells with high nuclear to cytoplasmic ratios, oval to elongated nuclei with perpendicular arrangement toward the lumens, and prominent nuclear overlapping. The stroma between these was minimal with the exception of two tumors. Calcifications and necrosis were absent. Immunohistochemically, the tumors were positive for KRT19 (7/7), PAX8 (5/5), cyclin D1 (6/6), KRT7 (5/7), and AMACR (1/5; focal, weak), and were negative for WT1, TTF1 (transcription termination factor-1), and thyroglobulin. In three of three tumors tested molecularly, EWSR1-PATZ1 fusion was identified by RNA sequencing and confirmed by RT-PCR and Sanger sequencing. Over a follow-up period of 1-7 years, no evidence of recurrence or metastasis has been detected. The EWSR1-PATZ1 fusion has been recognized as a recurrent alteration in a subset of round to spindle cell sarcomas with EWSR1-non-ETS fusions (EWSR1-PATZ1 sarcoma) and in several central nervous system tumors. The finding of an EWSR1-PATZ1 fusion in all three of the thyroid-like follicular renal cell carcinomas for which sufficient tissue was available for genomic profiling provides the first distinct molecular abnormality in thyroid-like follicular renal cell carcinomas, supporting its designation as a distinct diagnostic entity.

Incidental occurrence of papillary renal cell carcinoma in the native kidney with autosomal dominant polycystic kidney disease after renal transplantation: A case report

Autosomal dominant polycystic kidney disease (ADPKD) is one of the best-known genetic diseases. Almost half of the patients with ADPKD will develop end-stage renal disease, and the majority of patients are treated with renal transplantation. The current study presents a case that developed papillary renal cell carcinoma (PRCC) in the native right kidney 10 years after renal transplantation. PRCC is a not common malignant tumour entity (18.5% of all cases of renal cell carcinoma) compared with common clear cell renal carcinoma (65-70% of all cases of RCC).

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.

Prognostic and Therapeutic Potential of the OIP5 Network in Papillary Renal Cell Carcinoma

Papillary renal cell carcinoma (pRCC) is an aggressive but minor type of RCC. The current understanding and management of pRCC remain poor. We report here OIP5 being a novel oncogenic factor and possessing robust prognostic values and therapeutic potential. OIP5 upregulation is observed in pRCC. The upregulation is associated with pRCC adverse features (T1P < T2P < CIMP, Stage1 + 2 < Stage 3 < Stage 4, and N0 < N1) and effectively stratifies the fatality risk. OIP5 promotes ACHN pRCC cell proliferation and xenograft formation; the latter is correlated with network alterations related to immune regulation, metabolism, and hypoxia. A set of differentially expressed genes (DEFs) was derived from ACHN OIP5 xenografts and primary pRCCs (n = 282) contingent to OIP5 upregulation; both DEG sets share 66 overlap genes. Overlap66 effectively predicts overall survival (p < 2 × 10^-16) and relapse (p < 2 × 10^-16) possibilities. High-risk tumors stratified by Overlap66 risk score possess an immune suppressive environment, evident by elevations in Treg cells and PD1 in CD8 T cells. Upregulation of PLK1 occurs in both xenografts and primary pRCC tumors with OIP5 elevations. PLK1 displays a synthetic lethality relationship with OIP5. PLK1 inhibitor BI2356 inhibits the growth of xenografts formed by ACHN OIP5 cells. Collectively, the OIP5 network can be explored for personalized therapies in management of pRCC patients.

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.

Papillary renal cell carcinoma: Review

Kidney cancer is the 13th most common malignancy globally, and the incidence is rising. Papillary renal cell carcinoma is the second most common subtype, comprising 10-15% of renal cell carcinomas. Though the histologic features of this subtype were initially described in the 1990's, our understanding of the genetic and molecular characteristics of this disease have rapidly evolved over the past decade. In this review, we summarize the contemporary understanding of the clinical, morphologic, radiographic, and genetic characteristics of papillary renal cell carcinoma, as well as clinical considerations, current options for management, and prognosis.

Identification of 4-genes model in papillary renal cell tumor microenvironment based on comprehensive analysis

BACKGROUND

The tumor microenvironment acts a pivotal part in the occurrence and development of tumor. However, there are few studies on the microenvironment of papillary renal cell carcinoma (PRCC). Our study aims to explore prognostic genes related to tumor microenvironment in PRCC.

METHODS

PRCC expression profiles and clinical data were extracted from The Cancer Gene Atlas (TCGA) and Gene Expression Omnibus (GEO) database. Immune/stromal scores were performed utilizing the ESTIMATE algorithm. Three hundred fifty-seven samples were split into two groups on the basis of median immune/stromal score, and comparison of gene expression was conducted. Intersect genes were obtained by Venn diagrams. Hub genes were selected through protein-protein interaction (PPI) network construction, and relevant functional analysis was conducted by DAVID. We used Kaplan-Meier analysis to identify the correlations between genes and overall survival (OS) and progression-free survival (PFS). Univariate and multivariate cox regression analysis were employed to construct survival model. Cibersort was used to predict the immune cell composition of high and low risk group. Combined nomograms were built to predict PRCC prognosis. Immune properties of PRCC were validated by The Cancer Immunome Atlas (TCIA).

RESULTS

We found immune/stromal score was correlated with T pathological stages and PRCC subtypes. Nine hundred eighty-nine differentially expressed genes (DEGs) and 1169 DEGs were identified respectively on the basis of immune and stromal score. Venn diagrams indicated that 763 co-upregulated genes and 4 co-downregulated genes were identified. Kaplan-Meier analysis revealed that 120 genes were involved in tumor prognosis. Then PPI network analysis identified 22 hub genes, and four of which were significantly related to OS in patients with PRCC confirmed by cox regression analysis. Finally, we constructed a prognostic nomogram which combined with influence factors.

CONCLUSIONS

Four tumor microenvironment-related genes (CD79A, CXCL13, IL6 and CCL19) were identified as biomarkers for PRCC prognosis.

Exploration of immune-related genes in high and low tumor mutation burden groups of chromophobe renal cell carcinoma

Renal cell carcinoma (RCC) is one of most common cancers with gradually increasing incidence and high mortality. Chromogenic RCC (chRCC) is the third most common histological subtype of RCC, accounting for approximately 5–7% of RCC. In our study, the transcriptome expression profile data (n=89) of chRCC, corresponding clinical data (n=113) and the somatic mutation data (n=66) were obtained from the TCGA database. We first analyzed the mutation data of chRCC patients and divided chRCC patients into high and low tumor mutation burden (TMB) groups based on the median TMB. We found that high TMB was significantly associated with worse prognosis and could promote tumor metastasis and development. Moreover, four different immune-related genes (BIRC5, PDGFRL, INHBE, IL20RB) were also identified. We found that BIRC5 was significantly overexpressed in the high TMB group and correlated with worse prognosis. The results of univariate and multivariate COX analyses demonstrated that BIRC5 (hazard ratio (HR) = 2.094) may serve as a prognostic indicator for patients with chRCC with high TMB. In addition, we identified the possible functional pathways of BIRC5 through gene set enrichment analysis (GSEA) enrichment. A positive correlation was obtained between BIRC5 and the abundance of CD4⁺ T cells. The results of our study revealed their correlation between the immune-related genes and clinicopathologic features as well as potential functional pathways as well as immune infiltrating cells, which may provide more data about the development of chRCC immunotherapy.

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.

Anti-tumor efficacy of human anti-c-met CAR-T cells against papillary renal cell carcinoma in an orthotopic model

Chimeric antigen receptor (CAR)‐T cell therapy has shown salient efficacy in cancer immunotherapy, particularly in the treatment of B cell malignancies. However, the efficacy of CAR‐T for solid tumors remains inadequate. In this study, we displayed that c‐met is an appropriate therapeutic target for papillary renal cell carcinoma (PRCC) using clinical samples, developed an anti‐human c‐met CAR‐T cells, and investigated the anti‐tumor efficacy of the CAR‐T cells using an orthotopic mouse model as pre‐clinical research. Administration of the anti‐c‐met CAR‐T cells induced marked infiltration of the CAR‐T cells into the tumor tissue and unambiguous suppression of tumor growth. Furthermore, in combination with axitinib, the anti‐tumor efficacy of the CAR‐T cells was synergistically augmented. Taken together, our current study demonstrated the potential for clinical application of anti‐c‐met CAR‐T cells in the treatment of patients with PRCC.

An unusual outcome of papillary renal cell carcinoma with lung metastases: a case report and review of literature

Background

Renal cell carcinoma (RCC) is a heterogeneous group of malignant epithelial tumors of the kidney. It accounts for more than 90% of all kidney cancers. However, papillary RCC is the second most common histologic subtype representing 10–15% of all RCCs. The mean age of presentation for papillary RCC ranges between 59 and 63 years but more importantly when RCC is diagnosed at a younger age, the possibility of an underlying hereditary kidney cancer syndrome should be considered. RCC potentially metastasizes to many different organs with lung being the commonest site accounting for 45.2%. The treatment for metastatic RCC is mostly multimodal for most patients. However, patients with untreated pulmonary metastases have been observed to have very poor prognosis with a 5-year overall survival rate of only 5% or even less and thus the need to report on the unusual outcome of our patient who had a metastatic disease.

Case presentation

The present study reports a papillary renal cell carcinoma with multiple lung metastases in a 31-year-old woman who presented with progressive right flank mass and pain with no chest symptoms. She underwent cytoreductive radical nephrectomy via a right subcostal incision. Patient, however, did not undergo metastasectomy nor palliative systemic therapy and was seen 5 years post-nephrectomy.

Conclusion

Our patient with metastatic RCC, without undergoing metastasectomy nor palliative systemic therapy, remained stable with 5-year progression-free survival post-cytoreductive nephrectomy.

The effect of the papillary renal cell carcinoma subtype on oncological outcomes

The study aimed to compare the clinicopathological features and prognosis between type I and type II papillary renal cell carcinoma (PRCC) and to investigate whether the subtypes of PRCC would affect oncological outcomes. A total of 102 patients with PRCC were recruited, of which 42 were type I PRCC and 60 type II. The clinicopathological features and oncologic outcomes of the patients were evaluated. The type II cases had a higher WHO/ISUP grading (P < 0.001), T (P = 0.003), N (P = 0.010) stage and stage grouping (P = 0.011) than the type I. During a median follow-up period of 61.4 months, 1-year cancer specific survival (CSS) of the type I was 100%, 5-year CSS was 95.2%, the 1-year CSS of the type II was 96.2%, and 5-year CSS was 75.7%. The univariate analysis showed that subtype, symptoms, TNM, stage grouping, WHO/ISUP grading and surgical methods appeared to affect prognosis of the patients with PRCC. However, multivariate analysis revealed that only stage grouping was the independent risk factor. After the stage grouping factor was adjusted for the analysis, there were no statistically significant differences in CSS (P = 0.214) and PFS (P = 0.190) between the localized type I and type II PRCC groups. Compared with type I PRCC, type II had higher pathological T, N stage and WHO/ISUP grading. However, it was the Stage grouping that made a great difference to oncological outcomes, rather than the subtype of PRCC.

Development of an Autophagy Score Signature for Predicting Overall Survival in Papillary Renal Cell Carcinoma

Background

Autophagy is considered to be closely associated with cancer, functioning as either an anticancer or procancer mechanism depending on the cancer stage. However, the prognostic value of autophagy on papillary renal cell carcinoma (pRCC) remains unclear. In this study, our purpose was to determine the autophagy-related mRNA signature to predict the overall survival of patients with pRCC.

Materials and Methods

A total of 284 patients with pathologic confirmed pRCC in The Cancer Genome Atlas (TCGA) dataset were recruited and included. We choose patients who have smoked less than 15 years but staging 3 or 4 (including nontobacco exposure) vs. more than 15 years but staging 1 or 2. Fourteen differentially expressed mRNAs were found with fold change > 2 and P value < 0.001 through limma package after making a pair between nontobacco exposure or less than 15 years and tobacco exposure more than 15 years by matchIt package.

Results

Six mRNAs were identified to be significantly associated with overall survival. Then, using a risk score based on the signature of these six mRNAs, we divided the patients into low-risk and high-risk groups with significantly different OS. Further multivariate Cox regression analyses revealed that the 6-mRNA signature was independent of age, TNM stage, and tumor type. In the present study, a novel 6-mRNA signature that is useful in survival prediction in pRCC patients was developed. If validated, this mRNA signature might assist in selecting high-risk subpopulation that needs more aggressive therapeutic intervention. The risk score involved in several cancer-related pathways was identified using gene set enrichment analysis.

Conclusion

We initially generated a six autophagy-related genes' signature, which correlates with AJCC N stage, tumor type, and pathological stage and independently predicts OS.

Routine or enhanced imaging to differentiate between type 1 and type 2 papillary renal cell carcinoma

AIM

To investigate imaging features and differentiating qualities of type 1 and type 2 papillary renal cell carcinoma (pRCC) by different imaging techniques.

MATERIALS AND METHODS

From 2007 to 2019, 107 patients with type 1 pRCC (T1-pRCC) and 147 with type 2 pRCC (T2-pRCC) were included in this retrospective study. All patients underwent conventional ultrasound (US); some also underwent contrast-enhanced ultrasound (CEUS), contrast-enhanced computed tomography (CECT), or contrast-enhanced magnetic resonance imaging (CE-MRI). Tumour Fuhrman grade or World Health Organization (WHO)/International Society of Urological Pathology (ISUP) grade (after June 2016) and invasive ranges were recorded. The two types of pRCC were analysed and compared for imaging features including tumour position, size, margin, echo type, and colour Doppler flow imaging (CDFI) using US as well as enhanced features from CEUS, CECT, or CE-MRI.

RESULTS

T2-pRCC showed a higher Fuhrman grade (p<0.001) and greater propensity to invade extrarenal tissue (p<0.001) than T1-pRCC. On US imaging, T2-pRCC was more likely to be a cystic-solid lesion (p<0.001), and colour flow with a higher resistance index (RI; p=0.014) was more easily detected (p=0.001) in T2-pRCC than in T1-pRCC. Within contrast-enhanced examinations, more T2-pRCC lesions had blurred tumour borders (p=0.003), hypervascular characteristics (p=0.003), and heterogeneous enhancement (p<0.001) than those of T1-pRCC.

CONCLUSIONS

T2-pRCC manifests more aggressively than T1-pRCC. T2-pRCC has a higher proportion of hypervascular and heterogeneous enhancement than T1-RCC.

Biphasic Squamoid Alveolar Renal Cell Carcinoma of the Kidney Involved by Atypical CD5-Positive B-Cells

Biphasic squamoid alveolar renal cell carcinoma (BSARCC) is a recently described kidney cancer entity with <60 published cases so far. Some unique features of BSARCC include distinct squamoid and alveolar morphology forming glomeruloid configurations and 2 types of tumor cells with different immunoprofiles. Although the mechanism is unknown, neutrophils and cellular materials engulfed by larger tumor cells (described as "emperipolesis") are observed in all reported cases including the current one. In this article, we report a case of a 70-year-old man who presented with an incidental renal mass during workup for immunoglobulin M monoclonal gammopathy of unknown significance and cold agglutinin autoimmune hemolytic anemia. A detailed pathologic evaluation and immunohistochemical studies revealed BSARCC colliding with atypical CD5+ monoclonal B-cells.

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.

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.

Characterization of PD-1 and PD-L1 Expression in Papillary Renal Cell Carcinoma: Results of a Large Multicenter Study

BACKGROUND

Programmed cell death protein 1 (PD-1)/programmed death-ligand 1 (PD-L1) play a decisive role as prognostic markers in clear-cell renal cell carcinoma (RCC). To date, the role of PD-1/PD-L1 as a prognostic marker in papillary RCC (pRCC) remains scarce.

PATIENTS AND METHODS

Patients' sample collection was a joint collaboration of the nationwide PANZAR consortium - a multicenter study. Medical history and tumor specimens were collected from 245 and 129 patients with pRCC types 1 and 2, respectively. Expression of PD-1 and PD-L1 was determined by immunohistochemistry in pRCC and tumor-infiltrating mononuclear cells.

RESULTS

Of 374 pRCC specimens, 204 type 1 and 97 type 2 were evaluable for PD-1 and PD-L1 expression analysis. In total, PD-1 and PD-L1 expression were found in 8 (4.9%) of 162 and 12 (7.2%) of 166 evaluable pRCC type 1 specimens. Comparably, PD-1 and PD-L1 expression were found in 2 (2.4%) of 83 and 5 (6.2%) of 81 evaluable pRCC type 2 specimens. Hardly any clinically relevant associations between PD-1 and PD-L1 positivity and clinicopathologic or clinical courses were observed, neither in pRCC type 1 nor type 2.

CONCLUSION

The analysis of a large pRCC cohort from a multicenter consortium revealed no impact of PD-1/PD-L1 expression on prognosis in patients with pRCC with predominantly limited disease status, neither for type 1 nor type 2. However, the impact of PD-1 and PD-L1 in more advanced pRCC disease needs further elucidation.

Are immune checkpoint inhibitors a valid option for papillary renal cell carcinoma? A multicentre retrospective study

BACKGROUND

Papillary renal cell carcinoma (pRCC) is the most common non-clear cell RCC (nccRCC). Pivotal studies evaluating immune checkpoint inhibitors mostly excluded nccRCC. The aim of this retrospective and multicentre study was to evaluate the activity of programmed death-1 (PD-1)/ programmed death-ligand 1 (PD-L1) inhibitors specifically in metastatic pRCC.

METHODS

The primary end-point was time to treatment failure (TTF). Secondary endpoints included objective response rate (ORR), overall survival (OS) and treatment-related adverse events (TRAEs).

RESULTS

From 02/2016 to 01/2019, 57 patients with pRCC were included. Histology included 16 (28%) type 1 pRCC, 34 (60%) type 2 pRCC and 7 (12%) unclassified pRCC. Treatment with immune checkpoint inhibitors was used in the first-line setting in 4 patients (7%), in the second-line setting in 32 patients (56%) and in the third-line setting or more in 21 patients (37%). With a median follow-up of 12 months (95% confidence interval [CI]: 9.9-21.0), the median TTF was 3.1 months (95% CI: 2.7-5.0). Among the 55 patients evaluable for ORR, best response was complete response/partial response in 6 patients (11%), stable disease in 18 patients (33%) and progressive disease in 31 patients (56%). The median OS was 14.6 months (95% CI: 9.0- not reached). TRAEs of grade III-IV were noted in 6 patients (10%) leading to treatment discontinuation, and no grade V TRAEs were observed.

CONCLUSION

PD-1/PD-L1 inhibitors exhibit limited activity as monotherapy in this pRCC population, which remains an unmet need. Our findings underline the need for further prospective clinical trials evaluating immune checkpoint inhibitor combinations in patients with pRCC.

Eosinophilic cytoplasmic inclusions in type 2 papillary renal cell carcinoma

A case of a patient with type 2 papillary renal cell carcinoma with eosinophilic cytoplasmatic inclusions is presented. About 50% of tumor cells were characterized by a well-circumscribed intra-cytoplasmatic round-to-oval or irregular inclusion/globule. Inclusions were 7-30 micron in diameter. They were glassy and pale to slightly eosinophilic in color in hematoxylin and eosin, were stained red by trichrome and were negative for periodic acid-Schiff reaction. Immunohistochemically, globules were negative for PAX8, epithelial membrane antigen, Carbonic Anhydrase IX, pan-cytokeratin (AE1/AE3), CD10, S100 protein, α-smooth-muscle actin, cytokeratin 7 and cytokeratin 34βE12. Glassy hyaline globules were not detected in any adjacent normal kidney cells. The presence of eosinophilic cytoplasmic inclusions in renal cell carcinoma, especially in papillary renal cell carcinoma, has been rarely emphasized in the literature. In this article, we review similar cases in the literature and discuss the nature of eosinophilic globules.

Identification of methylation-driven genes related to the prognosis of papillary renal cell carcinoma: a study based on The Cancer Genome Atlas

Background

Aberrant DNA methylation patterns are involved in the pathogenesis of papillary renal cell carcinoma (pRCC). This study aimed to investigate the potential of methylation-driven genes as biomarkers in determining the prognosis of pRCC by bioinformatics analysis.

Methods

DNA methylation and transcriptome profiling data were downloaded from The Cancer Genome Atlas database. Methylation-driven genes (MDGs) were obtained using MethylMix R package. A Cox regression model was used to screen for pRCC prognosis-related MDGs, and a linear risk model based on MDG methylation profiles was constructed. A combined methylation and gene expression survival analysis was performed to further explore the prognostic value of MDGs independently.

Results

A total of 31 MDGs were obtained. Univariate and multivariate Cox regression analysis identified eight genes (CASP1, CD68, HOXD3, HHLA2, HOXD9, HOXA10-AS, TMEM71, and PLA2G16), which were used to construct a predictive model associated with overall survival in pRCC patients. Combined DNA methylation and gene expression survival analysis revealed that C19orf33, GGT6, GIPC2, HHLA2, HOXD3, HSD17B14, PLA2G16, and TMEM71 were significantly associated with patients’ survival.

Conclusion

Through the analysis of MDGs in pRCC, this study identified potential biomarkers for precision treatment and prognosis prediction, and provided the basis for future research into the molecular mechanism of pRCC.

Anti-angiogenesis and Immunotherapy: Novel Paradigms to Envision Tailored Approaches in Renal Cell-Carcinoma

Although decision making strategy based on clinico-histopathological criteria is well established, renal cell carcinoma (RCC) represents a spectrum of biological ecosystems characterized by distinct genetic and molecular alterations, diverse clinical courses and potential specific therapeutic vulnerabilities. Given the plethora of drugs available, the subtype-tailored treatment to RCC subtype holds the potential to improve patient outcome, shrinking treatment-related morbidity and cost. The emerging knowledge of the molecular taxonomy of RCC is evolving, whilst the antiangiogenic and immunotherapy landscape maintains and reinforces their potential. Although several prognostic factors of survival in patients with RCC have been described, no reliable predictive biomarkers of treatment individual sensitivity or resistance have been identified. In this review, we summarize the available evidence able to prompt more precise and individualized patient selection in well-designed clinical trials, covering the unmet need of medical choices in the era of next-generation anti-angiogenesis and immunotherapy.

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.