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a-Methylacyl coenzyme A racemase (AMACR) is traditionally considered to be a marker of papillary renal cell carcinoma. However, AMACR expression can be seen in other renal tumors. The aim of this study was to investigate AMACR immunoreactivity within the spectrum of clear cell renal cell neoplasms. Fifty-three clear cell renal epithelial tumors were used in assembling the following four cohorts: low grade (LG) clear cell renal cell carcinoma (CCRCC), high grade (HG) CCRCC, CCRCC with cystic changes, and multilocular cystic renal neoplasm of low malignant potential (MCRNLMP). Representative blocks were stained for AMACR, using two different clones (SP52 and OV-TL12/30). There were at least some AMACR immunoreactivity in 77.8 % and 68.9 % of CCRCCs (using SP52 and OV-TL12/30 clone, respectively). Moderate to strong positivity, or positivity in more than one third of the tumor (even weak in intensity) was detected in 46.7 % of CCRCCs using SP52 and in 48.9 % of CCRCC using OV-TL12/30 clone. The highest AMACR reactivity was observed in HG CCRCC (60 % by SP52 and 66.7 % by OV-TL12/30). Strong and diffuse AMACR positivity was detected in 8.9 % of all CCRCCs. AMACR immunoreactivity in MCRNLMP was 37.5 % (SP52 clone) and 25 % (OV-TL12/30 clone). We demonstrated relatively high expression rate of AMACR in CCRCC, while very variable in intensity and distribution. This finding may have diagnostic implications especially in limited samples (i.e., core biopsies), as AMACR positivity does not exclude the diagnosis of CCRCC., Competing Interests: Declaration of competing interest The authors declare no financial interests or personal relationships that could have appeared to influence the work reported in this paper. Ondrej Fiala received honoraria from Novartis, Janssen, Merck and Pfizer for consultations and lectures unrelated to this project., (Copyright © 2024 Elsevier Inc. All rights reserved.)

Predicting the clinical behavior and trajectory of chromophobe renal cell carcinoma (ChRCC) by histologic features has so far proven to be challenging. It is known that ChRCC represents a heterogeneous group of neoplasms demonstrating variable, yet distinctive morphologic and genetic profiles. In this international multi-institutional study, we aimed to assess the impact of histologic diversity in ChRCC (classic/eosinophilic versus rare subtypes) on survival outcome. This is an international multi-institutional matched case-control study including 14 institutions, examining the impact of histologic subtypes of ChRCC on survival outcome. The study group (cases) included 89 rare subtypes of ChRCC. The control group consisted of 70 cases of ChRCC including classic and eosinophilic features, age- and tumor size-matched. Most of the rare subtypes were adenomatoid cystic/pigmented ChRCC (66/89, 74.2%), followed by multicystic ChRCC (10/89, 11.2%), and papillary ChRCC (9/89, 10.1%). In the control group, there were 62 (88.6%) classic and 8 (11.4%) eosinophilic ChRCC. There were no statistically significant differences between the study and control groups for age at diagnosis, gender distribution, tumor size, presence of tumor necrosis, presence of sarcomatoid differentiation, and adverse outcomes. No statistically significant differences were found in clinical outcome between the rare subtypes and classic/eosinophilic groups by tumor size, necrosis, and sarcomatoid differentiation. Further, no statistically significant differences were found in clinical outcome between the two groups, stratified by tumor size, necrosis, and sarcomatoid differentiation. Our findings corroborated previous studies that both sarcomatoid differentiation and tumor necrosis were significantly associated with poor clinical outcome in classic/eosinophilic ChRCC, and this was proven to be true for ChRCC with rare histologic subtypes as well. This study suggests that rare morphologic patterns in ChRCC without other aggressive features play no role in determining the clinical behavior of the tumor., (Copyright © 2022 Elsevier Inc. All rights reserved.)

Clear cell renal cell carcinoma (CCRCC) is well known for intratumor heterogeneity. An accurate mapping of the tumor is crucial for assessing prognosis, and perhaps this can be linked to potential success/failure of targeted therapies. We assembled a cohort of 7 CCRCCs with prominent vasculature and microvascular hyperplasia (ccRCCPV), resembling those seen in high grade gliomas. A control group of classic CCRCC with no variant morphologies was also included. Both groups were analyzed for clinicopathologic, morphologic, immunohistochemical, and molecular genetic features. No statistically significant differences in mRNA expression of studied genes between the two groups were found. Using NGS panel Trusight Oncology 500 (TSO500), only one clinically significant gene mutation, VHL c.263G > A, p. (Trp88Ter), was found. TMB (Tumor Mutation Burden) and MSI (MicroSatellite Instability) were low, and no copy number variations (CNVs) were detected in the study cohort. Prominent microvascular hyperplasia in CCRCC is a rare phenomenon. From molecular genetic point of view, these tumors do not appear to be different from classic CCRCC. Prognostically, they also demonstrated similar clinical behaviors., (Copyright © 2021 Elsevier Inc. All rights reserved.)

So-called oncocytic papillary renal cell carcinoma (OPRCC) is a poorly defined variant of papillary renal cell carcinoma. Since its first description, several studies were published with conflicting results, and thus precise definition is lacking. A cohort of 39 PRCCs composed of oncocytic cells were analyzed. Cases were divided into 3 groups based on copy number variation (CNV) pattern. The first group consisted of 23 cases with CNV equal to renal oncocytoma. The second group consisted of 7 cases with polysomy of chromosomes 7 and 17 and the last group of 9 cases included those with variable CNV. Epidemiologic, morphologic and immunohistochemical features varied among the groups. There were not any particular histomorphologic features correlating with any of the genetic subgroups. Further, a combination of morphologic, immunohistochemical, and molecular-genetic features did not allow to precisely predict biologic behavior. Owing to variable CNV pattern in OPRCC, strict adherence to morphology and immunohistochemical profile is recommended, particularly in limited samples (i.e., core biopsy). Applying CNV pattern as a part of a diagnostic algorithm can be potentially misleading. OPRCC is a highly variable group of tumors, which might be misdiagnosed as renal oncocytoma. Using the term OPRCC as a distinct diagnostic entity is, thanks to its high heterogeneity, questionable., (Copyright © 2021 Elsevier Inc. All rights reserved.)

Although typically arranged in solid alveolar fashion, chromophobe renal cell carcinoma (RCC) may also show several other architectural growth patterns. We include in this series 8 chromophobe RCC cases with prominent papillary growth, a pattern very rarely reported or only mentioned as a feature of chromophobe RCC, which is lacking wider recognition The differential diagnosis of such cases significantly varies from the typical chromophobe RCC with its usual morphology, particularly its distinction from papillary RCC and other relevant and clinically important entities. Of 972 chromophobe RCCs in our files, we identified 8 chromophobe RCCs with papillary growth. We performed immunohistochemistry and array Comparative Genomic Hybridisation (aCGH) to investigate for possible chromosomal aberrations. Patients were 3 males and 5 females with age ranging from 30 to 84 years (mean 57.5, median 60 years). Tumor size was variable and ranged from 2 to 14 cm (mean 7.5, median 6.6 cm). Follow-up was available for 7 of 8 patients, ranging from 1 to 61 months (mean 20.1, median 12 months). Six patients were alive with no signs of aggressive behavior, and one died of the disease. Histologically, all cases were composed of dual cell population consisting of variable proportions of leaf-like cells with pale cytoplasm and eosinophilic cells. The extent of papillary component ranged from 15 to 100% of the tumor volume (mean 51%, median 50%). Sarcomatoid differentiation was identified only in the case with fatal outcome. Immunohistochemically, all tumors were positive for CK7, CD117 and Hale's Colloidal Iron. PAX8 was positive in 5 of 8 cases, TFE3 was focally positive 3 of 8 tumors, and Cathepsin K was focally positive in 2 of 8 tumors. All cases were negative for vimentin, AMACR and HMB45. Fumarate hydratase staining was retained in all tested cases. The proliferative activity was low (up to 1% in 7, up to 5% in one case). Three cases were successfully analyzed by aCGH and all showed a variable copy number variation profile with multiple chromosomal gains and losses. CONCLUSIONS: Chromophobe RCC demonstrating papillary architecture is an exceptionally rare carcinoma. The diagnosis can be challenging, although the cytologic features are consistent with the classic chromophobe RCC. Given the prognostic and therapeutic implications of accurately diagnosis other RCCs with papillary architecture (i.e., Xp11.2 translocation RCC, FH-deficient RCC), it is crucial to differentiate these cases from chromophobe RCC with papillary architecture. Based on this limited series, the presence of papillary architecture does not appear to have negative prognostic impact. However, its wider recognition may allow in depth studies on additional examples of this rare morphologic variant., Competing Interests: Declaration of competing interest All authors declare no conflict of interest., (Copyright © 2019 Elsevier Inc. All rights reserved.)

Papillary renal cell carcinoma (PRCC) is currently a well-studied type of RCC. In addition to PRCC type 1, there are a number of other subtypes and variants of PRCCs which have been reported. We describe a series of 6 PRCCs with papillary, micropapillary and/or tubulopapillary architecture and prominent spindle cell stroma, resembling stroma in mixed epithelial and stromal tumor of the kidney (MESTK) or sarcomatoid RCC. Clinicopathologic, morphologic, immunohistochemical and molecular features were analyzed. All patients were males with an age range of 44-98 years (mean 65.3, median 65.5 years). Tumor size ranged from 2.4-11.4 cm (mean 5.8, median 4.5 cm). Follow-up data were available for 4 patients, ranging from 3 to 96 months (mean 42.75, median 36 months). Epithelial cells were mostly cylindrical with eosinophilic cytoplasm, showing nuclear grade 2 and 3 (ISUP/WHO). In all cases, loose to compact prominent stroma composed of spindle cells, without malignant mesenchymal heterologous elements was detected. No atypical mitoses were found, while typical mitoses were rare in both epithelial and stromal components. Epithelial cells were positive for CK7, AMACR, and vimentin in all cases, while negative for TFE3, HMB45, desmin, CD34, and actin. The stroma was positive for vimentin, actin and focally for CD34, while negative for CK7, AMACR, TFE3, HMB45, and desmin. Estrogen and progesterone receptors were completely negative. FH and SDHB expression was retained in all analyzable cases. Proliferative index was barely detectable in stromal component and low in epithelial component, ranging 0 to 5% positive stained cells/high power field. Copy number variation was variable with no distinct pattern. No mutations in CDKN2A, BAP1, MET were detected. PRCC with MESTK-like features is a distinct variant of PRCC mimicking MESTK. Our findings add to the body of literature on ever expanding variants of PRCCs. Both epithelial and stromal components lacked true Müllerian features, which was also proven by immunohistochemistry., Competing Interests: Declaration of competing interest All authors declare no conflict of interest., (Copyright © 2019 Elsevier Inc. All rights reserved.)

Clear cell renal cell carcinoma (CRCC) is well known for its intratumoral heterogeneity. Paneth-like cells (PLC) have been reported in variable organs (i.e., hepatobiliary, genitourinary, and female genital tract). In genitourinary system, it is possible to find PLCs in epididymis, urinary bladder and prostate. The objective of this study was to assess PLC in CRCCs 13 CRCCs with prominent PLC (CRCCPLC) were selected out of 1378 CRCCs in our registry. The tumors were analyzed using morphologic, immunohistochemical, ultrastructural, and molecular genetic methods. CRCCPLCs were mostly of low histologic grade (12/13). Immunohistochemical profile was compatible with classic CRCC. PLC constituted 10 to-70% of the tumor volume (mean 17.7%, median 10%). PLCs did not express neuroendocrine markers (chromogranin, synaptophysin, CD56, INSM-1). Ultrastructurally, PLCs were filled by membrane bounded vesicles of various sizes and were compatible with secretory type of cells. VHL mutation was found in 9/9 cases, and LOH3p was found in 6/8 analyzable cases. Conclusions: PLC morphology can variably be present in "classic" CRCC, even in a substantial proportion. Ultrastructurally, PLCs have all attributes of secretory cells. Preliminary follow up data showed that these tumors may not be associated with aggressive clinical behavior., (Copyright © 2019 Elsevier Inc. All rights reserved.)

Hereditary leiomyomatosis and renal cell carcinoma-associated renal cell carcinoma (HLRCC)/fumarate hydratase deficient renal cell carcinoma (FHRCC) is defined by molecular genetic changes (mutation/LOH in fumarate hydratase (FH) gene). We investigated chromosomal numerical aberration pattern (CNV) in FHRCC/HLRCC using array comparative genomic hybridization analysis and low pass whole genome sequencing. Genetic analysis was successfully completed in 12 tumors. Most common chromosomal aberrations detected were a complete or partial loss of chromosome 4 (5/12 cases), chromosome 15 (4/12 cases), and chromosomes 9, 13, and 14 (each in 3/12 cases), as well as a complete or partial gain of chromosome 17 (in 4/12 cases). No chromosomal losses or gains were detected in 4 cases. Copy number variation pattern in FHRCC/HLRCC appears to be highly variable and does not provide a useful diagnostic tool in identifying these cases. Immunohistochemical staining and especially molecular genetic evaluation of FH gene mutations/LOH remain the gold standard in identifying FHRCC/HLRCC., (Copyright © 2019. Published by Elsevier Inc.)

Clear cell renal cell carcinoma (ccRCC), the most common histologic subtype of RCCs, demonstrates a wide spectrum of morphologic features (i.e., low-grade spindle cell, syncytial giant cells, and mucin-producing cells). However, papillary growth pattern in ccRCCs is rather a rare finding, which can present challenges in differential diagnostic work up. The aim of this study was to investigate ccRCCs with predominant papillary features from morphologic, immunohistochemical and molecular genetic perspectives. 23 clear cell renal cell carcinomas with papillary architecture were selected. Tumors were evaluated morphologically, immunohistochemically, and molecularly by next-generation sequencing (NGS). The diagnosis of MiT family translocation RCC was excluded by TFE3 immunohistochemistry. Mean age of patients was 65.2 years (range 42-81 years), and 19/23 were male. Tumor size ranged from 1.6 to 12.8 cm (median 6.5 cm). At a median follow-up of 2.5 years (range 1.5-9 years), 2 patients (8.7%) died of disease, 2 developed metastasis. Areas of papillary pattern accounted for approximately 40-100% of the tumor. CK7 was negative in non-papillary areas in majority of cases (20/23, 87%), and was only focally positive in 3/23 cases (13%). In papillary areas, AMACR was positive/focally positive in 17/23 (73.9%) cases and in the non-papillary areas it was positive/focally positive in 22/23 (95.6%) cases. CAIX was mainly negative in both non-papillary and papillary areas (15/23 [65%] and 16/23 [69.5%], respectively). Molecular analysis of 15 analyzable cases revealed the most frequently mutated gene to be VHL (in 9 cases), followed by PRBM1 (in 2 cases) and 29 other different mutations in various genes. Papillary growth pattern in ccRCC is not an uncommon situation. Papillary RCC with clear cells and MiT family (TFE3) translocation RCCs are the major differential diagnostic considerations in such scenarios. Our NGS molecular analysis supported classifying such tumors as a morphologic variant of ccRCC., (Copyright © 2018 Elsevier Inc. All rights reserved.)

Background: We present a series of papillary renal cell carcinomas (PRCC) reminiscent of so-called "oncocytic variant of papillary renal cell carcinoma" (OPRCC), included in the 2016 WHO classification as a potential type 3 PRCC. OPRCC is a poorly understood entity, cytologically characterized by oncocytic cells with non-overlapping low grade nuclei. OPRCC is not genotypically distinct and the studies concerning this variant have shown an inconsistent genetic profile. The tumors presented herein demonstrated predominantly papillary/tubulopapillary architecture and differed from OPRCC by pseudostratification and grade 2-3 nuclei (Fuhrman/ISUP). Because there is a morphologic overlap between renal oncocytoma (RO) and PRCC in the cases included in this study, the most frequently affected chromosomes in RO and PRCC were analyzed., Materials and Methods: 147 PRCC composed of oncocytic cells were retrieved from our registry in order to select a group of morphologically uniform tumors. 10 cases with predominantly papillary, tubulopapillary or solid architectural patterns were identified. For immunohistochemical analysis, the following antibodies were used: vimentin, antimitochondrial antigene (MIA), AMACR, PAX8, CK7, CK20, AE1-3, CAM5.2, OSCAR, Cathepsin K, HMB45, SDHB, CD10, and CD117. Enumeration changes of locus 1p36, chromosomes 7, 14, 17, X, Y and rearrangement of CCND1 were examined by FISH. For further study, only tumors showing karyotype similar to that of RO were selected. The tumors exhibiting either trisomy of chromosomes 7, 17 or gain of Y, thus abnormalities characteristic for PRCC, were excluded., Results: There were 5 males and 5 females, with patient age ranging from 56 to 79 years (mean 66.8 years). The tumor size ranged from 2 to 10 cm (mean 5.1 cm). Follow-up was available for 8/10 patients (mean 5.2 years); one patient died of the disease, while 7 of 8 are alive and well. Immunohistochemically, all cases were reactive for AMACR, vimentin, PAX8, OSCAR, CAM5.2, and MIA. SDHB was retained in all cases. 9/10 cases were positive for CD10, 7/10 cases reacted with CK7, 4/10 with Cathepsin K, and 2/10 with AE1-3. None of the cases were positive for CD117, HMB45 and CK20. All 10 cases were analyzable by FISH and showed chromosomal abnormalities similar to that usually seen in RO (i.e. loss of 1p36 gene loci, loss of chromosome Y, rearrangement of CCND1 and numerical changes of chromosome 14)., Conclusions: We analyzed a series of renal tumors combining the features of PRCC/OPRCC and RO, that included pseudostratification and mostly high grade oncocytic cells lining papillary/tubulopapillary structures, karyotype characterized by loss of 1p36, loss of chromosome Y, rearrangement of CCND1 gene and numerical changes of chromosome 14. Despite the chromosomal numerical abnormalities typical of RO, we classified these tumors as part of the spectrum of PRCC because of their predominant papillary/tubulopapillary architecture, immunoprofile that included reactivity for AMACR, vimentin and lack of reactivity for CD117, all of which is incompatible with the diagnosis of RO. This study expands the morphological spectrum of PRCC by adding a cohort of diagnostically challenging cases, which may be potentially aggressive., (Copyright © 2018 Elsevier Inc. All rights reserved.)

Background: Recently, we came with the theory of a possible relationship between a group of testicular and pancreatic tumors. We used one case of a pancreatic analogue solid pseudopapillary neoplasm of the testis composed partially of areas reminiscent of solid pseudopapillary neoplasm (SPN) of the pancreas and partially of structures identical to primary signet ring stromal tumor of the testis (PSRSTT) as a connecting link between these two entities. After demonstrating that PSRSTT and pancreatic analogue SPN of the testis share the same immunoprofile and genetic features characteristic for pancreatic SPN, we came to the conclusion that pancreatic analogue SPN of the testis and PSRSTT represent a morphological spectrum of a single entity and that both are related to the pancreatic SPN., Design: The aim of this study is to present a series of 6 cases of testicular tumors, which lacked the signet ring cell component and were thus morphologically very similar to the SPN of the pancreas. The goal of this study is to compare the genetic background of these testicular tumors that are obviously related to the PSRSTT/pancreatic analogue SPN of the testis with the series of 8 pancreatic SPN., Results: The mutational analysis revealed an oncogenic somatic mutation in the exon 3 of the CTNNB1 (β-catenin) gene in all analyzable (5/6) testicular and all pancreatic (8/8) tumors. The immunoprofile (positivity with β-catenin, CD10, vimentin, NSE, CD56, and negativity with inhibin, calretinin, chromogranin) was identical in all testicular and pancreatic tumors., Conclusion: This study expanded the morphological spectrum of the PSRSTT/pancreatic analogue SPN of the testis by adding 6 cases without the signet ring cell component. Considering the obvious analogy of PSRSTT/pancreatic analogue SPN of the testis/SPN of the testis and their relationship to the pancreatic SPN we propose the collective term "solid pseudopapillary neoplasm of the testis" for these tumors. The mutational profile of the SPN of the testis and pancreas was the same in both groups of tumors which we consider as a final proof that SPN of the testis is identical to the SPN of the pancreas., (Copyright © 2018 Elsevier Inc. All rights reserved.)

Fumarate hydratase-deficient renal cell carcinoma (FH-RCC) is a rare and aggressive tumor affecting mostly younger patients. This is the first study to assess the expression of programmed death-1 (PD-1) receptor/PD-1 ligand (PD-L1) in FH-RCC. Formalin-fixed paraffin-embedded samples from 13 FH-RCCs collected in an international multi-institutional study, were evaluated by immunohistochemistry (IHC) for PD-1/PD-L1 reactivity in tumor cells and tumor infiltrating lymphocytes (TILs). PD-1/PD-L1 expression was further evaluated by qPCR. By IHC, PD-1 was negative in tumor cells in all 13 cases. PD-L1 was positive in tumor cells in 2/13 cases, weak positive in 7/13, and negative in 4/13 cases, respectively. In TILs, PD-1 was positive in 1/13, weak positive in 3/13, and negative in 9/13 cases. In TILs, PD-L1 was weak positive by IHC in 5/13, and negative in 8/13 cases, respectively. qPCR confirmed the result for 2 of 3 IHC weak positive PD-1 samples. Of 7 IHC weak positive samples (in tumor cells), PD-L1 mRNA was detected in all 7 tumors. The majority of FH-RCCs did not express PD-1/PD-L1 by IHC, which was confirmed by molecular analysis. PD-1/PD-L1 expression in FH-RCC is restricted to a proportion of cases which may benefit from targeted therapies., (Copyright © 2017 Elsevier Inc. All rights reserved.)

The authors present a distinctive perineurioma (PN) variant which morphologically strongly resembles monophasic fibrous synovial sarcoma (MSS). The patients were 3 males and 1 female. The age ranged from 15 to 61years (mean: 44years). Locations included the sole, lower jaw, palm and foot. The tumor size ranged from 1.3cm to 2.5cm in the largest dimension (mean 1.8cm). Morphologically, all tumors had an identical, monotonous appearance. The perineurial cells were closely packed and created a confluent cellular whorls and/or sheets in a scarce stroma, with only focally discernible long, slender cytoplasmic processes typical for perineurial differentiation. The nuclei were rounded or slightly elongated to tapered, without nuclear atypia. Mitoses were rare to completely absent. Atypical mitoses, hemorrhage, necrosis or calcifications were not present. The proliferative index (Ki-67) was 1-3%. All analyzed tumors were positive for EMA, Claudin-1, GLUT-1 and negative with S100 protein, CD34, OSCAR, CK7 and TLE-1. Two cases were tested by fluorescence in situ hybridization and neither showed alterations of the SYT gene. One case studied by electron microscopy showed characteristic features of perineurial differentiation. Follow-up was available for two patients both of which showed no evidence of disease at 8years and 6months, respectively. Based on their bland morphology, perineurial features and presumably benign clinical outcome we propose the term "whorling cellular perineurioma" for these tumors, which may represent an extremely cellular variant of sclerosing PN. Awareness of this PN subtype and its distinction from MSS is of utmost clinical significance., (Copyright © 2017 Elsevier Inc. All rights reserved.)

Oncocytic papillary renal cell carcinoma (PRCC) is a distinct subtype of PRCC, listed as a possible new variant of PRCC in the 2016 WHO classification. It is composed of papillae aligned by large single-layered eosinophilic cells showing linearly arranged oncocytoma-like nuclei. We analyzed clinicopathologic, morphologic, immunohistochemical and molecular-genetic characteristics of 11 oncocytic PRCCs with prominent tumor lymphocytic infiltrate, morphologically resembling Warthin's tumor. The patients were predominantly males (8/11, 73%), with an average age of 59years (range 14-76), and a mean tumor size of 7cm (range 1-22cm). Tumors had the features of oncocytic PRCCs with focal pseudostratification in 8/11 cases and showed dense stromal inflammatory infiltration in all cases. Papillary growth pattern was predominant, comprising more than 60% of tumor volume. Tubular and solid components were present in 5 and 3 cases, respectively. Uniform immunohistochemical positivity was found for AMACR, PAX-8, MIA, vimentin, and OSCAR. Tumors were mostly negative for carboanhydrase 9, CD117, CK20, and TTF-1. Immunohistochemical stains for DNA mismatch repair proteins MLH1 and PMS2 were retained in all cases, while MSH2 and MSH6 were negative in 1 case. Tumor infiltrating lymphocytes (TILs) consisted of both B and T cells. Chromosomal copy number variation analysis showed great variability in 5 cases, ranging from a loss of one single chromosome to complex genome rearrangements. Only one case showed gains of chromosomes 7 and 17, among other aberrations. In 4 cases no numerical imbalance was found. Follow up data was available for 9 patients (median 47.6months, range 1-132). In 6 patients no lethal progression was noted, while 3 died of disease. In conclusion, Warthin-like PRCC is morphologically very close to oncocytic PRCC, from which it differs by the presence of dense lymphoid stroma. Chromosomal numerical aberration pattern of these tumors is variable; only one case showed gains of chromosomes 7 and 17. Warthin-like PRCC is a potentially aggressive tumor since a lethal outcome was recorded in 3/9 cases., (Copyright © 2017 Elsevier Inc. All rights reserved.)

Background: Differentiated squamous intraepithelial lesion (dSIL) is morphologically and immunohistochemically analogous in the whole anogenital region. dSIL is a premalignant lesion frequently misinterpreted histopathologically as a benign dermatosis. The authors describe a peculiar change in the basal cell layer of the epidermis/epithelium overlying anogenital melanocytic nevi that may histopathologically imitate dSIL. The aim of this study is to familiarize the pathologists with this pitfall to avoid its possible overdiagnosis as dysplasia. Further, we tried to explore the biological characteristics of the dSIL-like changes and to focus on the differential diagnostic aspects., Design: Seventy cases of anogenital nevi were retrieved from our registry. All cases were stained with hematoxylin and eosin (H&E) and reviewed. Cases in which the epidermis overlying nevi featured atypical appearing basal keratinocytes in otherwise fully differentiated epithelium, variable degrees of acanthosis and parakeratosis were selected for additional investigation., Results: Thirty cases meeting the above described criteria were identified. The patients were 8 males and 22 females, with age at the time of diagnosis ranging from 4 to 68years. Follow-up data were available for 28 patients (range 0.5-19years, mean 5.1), and to date, no signs of epithelial malignancy have been recorded. Immunohistochemically (IHC), the epidermis overlying nevi showed insignificant positivity for p53 in all tested cases. Melanocytic markers (S-100 protein, SOX10, Melan A) and cytokeratin AE1/3 labeled melanocytes and keratinocytes, respectively, enabling their distinction, especially in nevi featuring a junctional component., Conclusions: Differentiated squamous intraepithelial lesion-like changes seem to occur relatively often in the epidermis overlying anogenital melanocytic nevi. Since morphologically they are virtually identical to the "true" dSIL, their distinction largely depends on p53 expression in basal keratinocytes with normal p53 expression in dSIL-like changes and diffuse nuclear/p53-null immunostaining in the "true" dSIL serving as an essential differential diagnostic tool. dSIL-like alterations seem to have no malignant potential, as to date, none of the patients included in this study have shown any signs of epithelial malignancy., (Copyright © 2016 Elsevier Inc. All rights reserved.)