Recurrent Tuberous Sclerosis Complex/Mammalian Target of Rapamycin Mutations Define Primary Renal Hemangioblastoma as a Unique Entity Distinct From Its Central Nervous System Counterpart.

ABSTRACT: Renal hemangioblastoma (HB) is a rare subset of HBs arising outside of the central nervous system (CNS), with its molecular drivers remaining entirely unknown. There were no significant alterations detected in previous studies, including von Hippel-Lindau gene alterations, which are commonly associated with CNS-HB. This study aimed to determine the real molecular identity of renal HB and better understand its relationship with CNS-HB. A cohort of 10 renal HBs was submitted for next-generation sequencing technology. As a control, 5 classic CNS-HBs were similarly analyzed. Based on the molecular results, glycoprotein nonmetastatic B (GPNMB) immunohistochemistry was further performed in the cases of renal HB and CNS-HB. Mutational analysis demonstrated that all 10 renal HBs harbored somatic mutations in tuberous sclerosis complex 1 ( TSC1 , 5 cases), TSC2 (3 cases), and mammalian target of rapamycin (2 cases), with the majority classified as pathogenic or likely pathogenic. The CNS-HB cohort uniformly demonstrated somatic mutations in the von Hippel-Lindau gene. GPNMB was strong and diffuse in all 10 renal HBs and completely negative in CNS-HBs, reinforcing the molecular findings. Our study reveals a specific molecular hallmark in renal HB, characterized by recurrent TSC/mammalian target of rapamycin mutations, which defines it as a unique entity distinct from CNS-HB. This molecular finding potentially expands the therapeutic options for patients with renal HB. GPNMB can be considered for inclusion in immunohistochemical panels to improve renal HB identification.

Loss of YAP1 C-terminus expression as an ancillary marker for metaplastic thymoma: a potential pitfall in detecting YAP1::MAML2 gene rearrangement.

AIMS: Metaplastic thymoma is a rare thymic tumour characterized by Yes Associated Protein 1 (YAP1) and Mastermind Like Transcriptional Coactivator 2 (MAML2) gene fusions resulting from an intrachromosomal inversion of chromosome 11. Immunohistochemistry with an antibody directed against the C-terminus of YAP1 has shown loss of expression in YAP1-rearranged vascular neoplasms, poromas, and porocarcinomas. This study aimed to validate an anti-YAP1 C-terminal antibody as an ancillary immunohistochemical marker for the diagnosis of metaplastic thymoma. MATERIALS AND METHODS: Ten metaplastic thymomas were selected for the current study. Fluorescence in situ hybridization (FISH), next-generation sequencing (NGS), and reverse transcription-polymerase chain reaction (RT-PCR) analyses were performed to detect YAP1::MAML2 fusions. We then performed immunohistochemistry to detect YAP1 C-terminus expression in 10 metaplastic thymomas, 50 conventional thymomas (10 each of type A thymoma, type AB thymoma, type B1 thymoma, type B2 thymoma, and type B3 thymoma) and seven thymic carcinomas. RESULTS: All 10 cases showed narrow split signals with a distance of nearly two signal diameters and sometimes had false-negative results in YAP1 and MAML2 break-apart FISH (BA-FISH). Abnormal colocalized signals of the YAP1::MAML2 fusion were observed in all 10 cases using fusion FISH (F-FISH) assays. Eight of 10 cases with adequate nucleic acids were successfully sequenced and all showed YAP1::MAML2 fusions; in two cases the fusions were detected by both DNA and RNA sequencing and in six cases by RNA sequencing only. YAP1::MAML2 fusion transcripts were identified in four cases by RT-PCR. Metaplastic thymoma showed loss of YAP1 C-terminus expression in all 10 (100%) cases. All other thymic neoplasms showed retained YAP1 C-terminus expression. CONCLUSION: YAP1 C-terminus immunohistochemistry is a highly sensitive and specific ancillary marker that distinguishes metaplastic thymoma from its mimics. BA-FISH assays could not effectively detect YAP1::MAML2 fusions due to the proximity of the two genes. Loss of YAP1 C-terminus expression is a reliable surrogate for the detection of YAP1::MAML2 fusions in metaplastic thymoma.

Thyroid-like low-grade nasopharyngeal papillary adenocarcinoma: a clinicopathological and molecular study of four cases.

Thyroid-like low-grade nasopharyngeal papillary adenocarcinoma (TLLGNPPA) is a rare nasopharyngeal carcinoma. To date, less than 60 cases of TLLGNPPA have been reported, and its clinical features and pathogenesis remain unclear. In this paper, four cases of TLLGNPPA were reported to clarify the clinicopathological and molecular features of this disease. Histopathological examination revealed that all tumors had papillary glandular arrangement, with a fibrovascular axis in the tumor stroma and focal nuclear groove. All tumors expressed pan-CK, CK7, and CK19, while TG and Pax-8 were negative, and the Ki-67 index was approximately 1-3%. The expression of TTF-1 was diffusely positive in two cases and focally positive in two cases. EBER was not expressed in four cases. Molecular testing was possible in three cases. No common driver event was noted, but unique, mutually exclusive molecular variants were found in each of the three tumors (FGFR4, PDK1, AXIN2, FOXL2, and PIK3C3), one also with copy number variants in MCL1 and STMN1. All four patients underwent surgical resection of the tumor and had no metastasis or recurrence from 7 to 60 months post-resection. Given the assertion that these tumors do not recur or metastasize in addition to their heterogeneous gene mutation spectrum, we propose that TLLGNPPA is a neoplasm with low malignant potential and should no longer to be referred to as an adenocarcinoma.

TSC/MTOR -associated Eosinophilic Renal Tumors Exhibit a Heterogeneous Clinicopathologic Spectrum : A Targeted Next-generation Sequencing and Gene Expression Profiling Study.

BACKGROUND: Several TSC1/2- or MTOR -mutated eosinophilic renal tumor subsets are emerging, including eosinophilic solid and cystic renal cell carcinoma (ESC RCC), eosinophilic vacuolated tumors (EVTs) and low-grade oncocytic tumors (LOTs). "Unclassified renal tumors with TSC/MTOR mutations" ( TSC -mt RCC-NOS) do not meet the criteria for other histomolecular subtypes. Whether these tumors represent a continuum of 1 TS C/ MTOR -mutation-associated disease is unknown. DESIGN: We evaluated the clinicopathologic and IHC profiles of 39 eosinophilic renal tumors with targeted DNA sequencing-confirmed TSC/MTOR mutations. Twenty-eight of these, plus 6 ChRCC, 5 RO, 5 ccRCC, 7 MiT RCC and 6 normal renal tissues, were profiled transcriptionally by RNA-seq. RESULTS: The 39 cases were reclassified based on morphological and IHC features as ESC RCC (12), EVT (9), LOT, (8) and TSC -mt RCC-NOS (10). The mutation profiles demonstrated consistency; ESC RCCs (12/12) had TSC mutations, and most LOTs (7/8) had MTOR mutations. Ten TSC -mt RCC-NOSs exhibited heterogeneous morphology, arising a differential diagnosis with other renal tumors, including MiT RCC, PRCC and epithelioid PEComa. RNA sequencing-based clustering segregated ESC RCC, EVT and LOT from each other and other renal tumors, indicating expression profile-level differences. Most TSC- mt RCC-NOSs (6/7) formed a mixed cluster with ESC RCC, indicating similar expression signatures; one TSC- mt RCC-NOS with unusual biphasic morphology clustered with EVT. CONCLUSIONS: We expanded the TSC/MTOR -associated eosinophilic renal tumor morphologic spectrum, identified gene mutation characteristics, and highlighted differential diagnosis challenges, especially with MiT RCC. ESC RCC, EVT, and LOT having distinct expression profiles. TSC -mt RCC-NOS may cluster with recognized TSC/MTOR -associated entities.

Solitary primary pulmonary synovial sarcoma: A case report.

BACKGROUND: Synovial sarcoma (SS) is an uncommon and highly malignant soft tissue sarcoma in the clinic, with primary pulmonary SS (PPSS) being extremely rare. Here, we describe the clinical characteristics, diagnosis, and treatment of a solitary PPSS case confirmed via surgical resection and fluorescence in situ hybridization (FISH). CASE SUMMARY: A 33-year-old man was admitted because of intermittent coughing and hemoptysis for one month, with lung shadows observed for two years. Whole-body positron emission tomography-computed tomography (PET-CT) revealed a solitary mass in the upper lobe of the right lung, with uneven radioactivity uptake and a maximum standardized uptake value of 5.6. The greyish-yellow specimen obtained following thoracoscopic resection was covered with small multi-nodulated structures and consisted of soft tissue. Hematoxylin and eosin staining revealed spindle-shaped malignant tumor cells. Immunohistochemistry indicated these tumor cells were CD99 and BCL-2-positive. Furthermore, the FISH test revealed synovial sarcoma translocation genetic reassortment, which confirmed the diagnosis of SS. CONCLUSION: PPSS is extremely rare and tends to be misdiagnosed as many primary pulmonary diseases. PET-CT, histologic analysis, and FISH tests can be used to differentiate PPSS from other diseases. Surgical resection is regularly recommended for the treatment of solitary PPSS and is helpful for improving the prognosis.

Clinicopathological and molecular characterization of biphasic hyalinizing psammomatous renal cell carcinoma: further support for the newly proposed entity.

The classification of renal neoplasms continues to evolve with novel, emerging, and provisional entities being described constantly. Biphasic hyalinizing psammomatous renal cell carcinoma (BHP RCC) associated with somatic NF2 mutations is one such new renal entity and is considered as a provisional category of RCC due to its very limited data. To provide further support for the newly proposed entity, we identified three additional cases of BHP RCC, with clinicopathological, immunohistochemical, and various molecular analyses. There were 2 males and 1 female, aged 65, 56, and 69 years, respectively. The neoplasms were unencapsulated, and all had a characteristic biphasic appearance of smaller cells clustering around basement membrane material within larger acini, forming pseudorosettes or a glomeruloid pattern. Hyalinized sclerotic stroma and psammoma bodies were abundant in two cases and focally present in one case. Focal areas of a less distinctive appearance were also noted; one additionally had an elongated tubular pattern in the myxoid stroma that is reminiscent of mucinous tubular and spindle cell carcinoma; one consisted solid alveolar architectures of epithelioid clear cells, bearing some resemblance to clear cell RCC. The neoplasms did not have a distinctive immunohistochemistry (IHC) profile, though all labeled for vimentin and CK7. Targeted DNA sequencing revealed that one case harbored a pathogenic somatic frameshift mutation in the NF2 gene, which was further confirmed by Sanger sequencing. The other two cases lacked NF2 mutations and instead demonstrated NF2 promoter methylation by methylation-specific polymerase chain reaction. Subsequent IHC assessment showed loss of expression of NF2 in all 3 cases, which evaluated NF2 status at the protein level. According to RNA sequencing-based clustering analysis, the 3 cases formed a distinct group with a shared specific transcriptional profile different from that of other established renal tumor types. In addition, phosphate inositide 3-kinase (PI3K)/AKT pathway was enriched significantly and on the top of all enriched pathways. Clinically, one patient developed bone metastases and died of disease two years after diagnosis. The other two patients had no evidence of recurrence or metastases, at 4- and 5-year follow-up. These findings not only validate previously described clinicopathological features but also expand the potentially genetic alterations and available clinical outcome data.

Low-grade oncocytic tumor of kidney harboring TSC/MTOR mutation: clinicopathologic, immunohistochemical and molecular characteristics support a distinct entity.

Low-grade oncocytic tumor (LOT) has recently been described as a distinct renal tumor. LOT shows consistent morphologic features and a CK7-positive/CD117-negative immunophenotype. To examine the clinicopathological, immunohistochemical, and molecular features of LOT, we searched our institutional archives and identified seven cases of LOT. All patients were female, with a mean age of 66 years (range 44-79 years). The average tumor size was 3.2 cm (range 1.6-5.5 cm). Macroscopically, the tumors showed tan-brown and solid cut surfaces. Microscopically, the tumors showed compact nested to solid growth pattern, three cases with areas of edematous stroma containing loosely connected small clusters, cords or dispersed single tumor cells. The tumor cells had uniformly round to oval nuclei with eosinophilic cytoplasm, and showed perinuclear halos. Two cases focally had nuclear irregularities and binucleated cells were occasionally seen in three cases. Immunohistochemically, diffuse positivity for CK7 and lack of CD117 expression were present in all cases. All of the tumors were negative for CD10, CK20, vimentin, CA9, TFE3, TFEB, HMB45, and Melan-A. All tumors were positive for MTOR and negative for Cathepsin-K. FH and SDHB were retained. Next generation sequencing identified genetic variations in the MTOR pathway related genes: TSC1 (4/7), TSC2 (5/7), and MTOR (1/7). All patients were alive and without disease progression, after a mean follow-up of 43 months (range 6-89 months). LOT is an uncommon eosinophilic renal neoplasm with unique morphological and characteristic immunophenotypic features, and may represent an emerging separate renal entity characterized by mutations in the TSC/MTOR pathway.

Malignant melanotic Xp11 neoplasms exhibit a clinicopathologic spectrum and gene expression profiling akin to alveolar soft part sarcoma: a proposal for reclassification.

The classification of the distinct group of mesenchymal neoplasms, first described as 'Xp11 translocation perivascular epithelioid cell tumor (PEComa)' and for which the term 'melanotic Xp11 neoplasm' or 'Xp11 neoplasm with melanocytic differentiation' has recently been proposed, remains challenging and controversial. We collected 27 melanotic Xp11 neoplasms, the largest series to date, for a comprehensive evaluation. Fourteen of the cases, together with eight alveolar soft part sarcomas (ASPS), nine conventional PEComas and a control group of seven normal tissues were submitted to RNA sequencing. Follow-up available in 22 patients showed 5-year overall survival and 5-year disease-free survival of 47.6 and 35.7%, respectively, which were similar to ASPS and significantly worse than conventional PEComa. Univariate analysis of location (occurring in the kidney versus not kidney), infiltrative growth pattern, nuclear pleomorphism, mitotic activity ≥2/50 high-power fields (HPF), necrosis and lymphovascular invasion were found to be associated with overall survival and/or disease-free survival. Multivariate analysis identified that location was the only factor found to independently correlate with disease-free survival. More importantly, RNA sequencing-based clustering analysis segregated melanotic Xp11 neoplasm and ASPS from other tumors, including conventional PEComa and Xp11 translocation renal cell carcinoma, and formed a compact cluster representative of the largely similar expression signature. Here we clearly define the true biologic nature of melanotic Xp11 neoplasms which are distinctive malignant mesenchymal tumors, rather than simply PEComa variants with occasionally unpredictable behavior. Meanwhile, melanotic Xp11 neoplasm and ASPS more likely represent phenotypic variants of the same entity, which is distinct from conventional PEComa and Xp11 translocation renal cell carcinoma. Based on these important findings, melanotic Xp11 neoplasm might be reclassified into a distinctive entity together with ASPS, independent from PEComa, in future revisions of the current WHO categories of tumors of soft tissue and bone for the improved reclassification. © 2020 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Clinicopathologic and Molecular Analysis of the TFEB Fusion Variant Reveals New Members of TFEB Translocation Renal Cell Carcinomas (RCCs): Expanding the Genomic Spectrum.

Xp11 renal cell carcinoma (RCC) with different gene fusions may have different clinicopathologic features. We sought to identify variant fusions in TFEB translocation RCC. A total of 31 cases of TFEB RCCs were selected for the current study; MALAT1-TFEB fusion was identified in 25 cases (81%, 25/31) using fusion probes. The remaining 6 cases (19%, 6/31) were further analyzed by RNA sequencing and 5 of them were detected with TFEB-associated gene fusions, including 2 ACTB-TFEB, 1 EWSR1-TFEB, 1 CLTC-TFEB, and 1 potential PPP1R10-TFEB (a paracentric inversion of the TFEB gene, consistent with "negative" TFEB split FISH result, and advising a potential diagnostic pitfall in detecting TFEB gene rearrangement). Four of the 5 fusion transcripts were successfully validated by reverse transcription-polymerase chain reaction and Sanger sequencing. Morphologically, approximately one third (29%, 9/31) of TFEB RCCs showed typical biphasic morphology. The remaining two thirds of the cases (71%, 22/31) exhibited nonspecific morphology, with nested, sheet-like, or papillary architecture, resembling other types of renal neoplasms, such as clear cell RCC, Xp11 RCC, perivascular epithelioid cell tumor (PEComa), or papillary RCC. Although cases bearing a MALAT1-TFEB fusion demonstrated variable morphologies, all 9 cases featuring typical biphasic morphology were associated with MALAT1-TFEB genotype. Accordingly, typical biphasic morphology suggests MALAT1-TFEB fusion, whereas atypical morphology did not suggest the specific type of fusion. Isolated or clustered eosinophilic cells were a common feature in TFEB RCCs, which may be a useful morphology diagnostic clue for TFEB RCCs. Clinicopathologic variables assessment showed that necrosis was the only morphologic feature that correlated with the aggressive behavior of TFEB RCC (P=0.004). In summary, our study expands the genomic spectrum and the clinicopathologic features of TFEB RCCs, and highlights the challenges of diagnosis and the importance of subtyping of this tumor by combining morphology and multiple molecular techniques.

Targeted next-generation sequencing revealed distinct clinicopathologic and molecular features of VCL-ALK RCC: A unique case from an older patient without clinical evidence of sickle cell trait.

Anaplastic lymphoma kinase (ALK)-rearranged renal cell carcinoma (RCC) is a novel entity of rare tumors with only 10 cases reported in the literature. Three RCC cases bearing VCL-ALK gene fusion were all young African American patients and associated with sickle cell trait notably. In contrast to the 3 reported cases, this neoplasm occurred in a middle-age woman (57 years old) without any evidence of sickle cell trait and demonstrated an infiltrating growth pattern with tubular, tubulopapillary, and tubulocystic structures, overlapping with collecting duct carcinoma and renal medullary carcinoma. Abundant intraluminal mucin was also noted significantly in the histologic sections. Immunostaining showed strong membranous labeling for ALK protein. We applied a large panel-targeted next-generation sequencing to explore the molecular alterations in the current case, revealing a driver oncogene VCL-ALK gene fusion co-occurring with pathogenic mutations in EP300 and TRRAP genes. Thereafter, fluorescence in situ hybridization assay was used to detect the ALK gene rearrangement. Reverse transcription polymerase chain reaction confirmed the presence of a VCL-ALK gene fusion, a fusion of VCL exon 16 to ALK exon 20. Our report draws the attention to the possibility that VCL-ALK genotype can be involved in older patients unassociated with sickle cell trait, also expanding the spectrum to ALK-rearranged RCC.

Genetic and epigenetic alterations of SDH genes in patients with sporadic succinate dehydrogenase-deficient gastrointestinal stromal tumors.

This study aimed to investigate the association of SDH gene mutations and promoter methylation with succinate dehydrogenase-deficient gastrointestinal stromal tumors (SDH-deficient GISTs) and to further discuss the potential molecular mechanisms underlying SDHB expression loss in these tumors. First, a total of 26 patients with SDH-deficient GISTs were selected by identifying the loss of SDHB protein expression and wild-type for KIT and PDGFRa mutations. Then SDH gene mutations and promoter methylation were detected by DNA sequencing and methylation-specific polymerase chain reaction, respectively, and the clinical and pathological data of SDH-deficient GISTs patients were collected and analyzed accordingly. The results of genetic testing demonstrated that 38.46% (10/26) of these patients harbored mutations in SDHB, SDHC, and SDHD genes (3 cases with double mutations). Besides, aberrant promoter methylation of SDH genes was detected in 10 out of 26 cases (38.46%), including 8 cases in SDHA gene, 3 cases in SDHB gene, 1 case in both SDHA and SDHB genes. It is suggested that SDH gene mutations and promoter methylation may contribute to the loss of SDH protein expression in sporadic SDH-deficient GISTs. This study indicated that the genetic and epigenetic alterations of SDH genes may occur during tumor formation.

RNA sequencing of Xp11 translocation-associated cancers reveals novel gene fusions and distinctive clinicopathologic correlations.

Both Xp11 translocation renal cell carcinomas and the corresponding mesenchymal neoplasms are characterized by a variety of gene fusions involving TFE3. It has been known that tumors with different gene fusions may have different clinicopathologic features; however, further in-depth investigations of subtyping Xp11 translocation-associated cancers are needed in order to explore more meaningful clinicopathologic correlations. A total of 22 unusual cases of Xp11 translocation-associated cancers were selected for the current study; 20 cases were further analyzed by RNA sequencing to explore their TFE3 gene fusion partners. RNA sequencing identified 17 of 20 cases (85%) with TFE3-associated gene fusions, including 4 ASPSCR1/ASPL-TFE3, 3 PRCC-TFE3, 3 SFPQ/PSF-TFE3, 1 NONO-TFE3, 4 MED15-TFE3, 1 MATR3-TFE3, and 1 FUBP1-TFE3. The results have been verified by fusion fluorescence in situ hybridization (FISH) assays or reverse transcriptase polymerase chain reaction (RT-PCR). The remaining 2 cases with specific pathologic features highly suggestive of MED15-TFE3 renal cell carcinoma were identified by fusion FISH assay. We provide the detailed morphologic and immunophenotypic description of the MED15-TFE3 renal cell carcinomas, which frequently demonstrate extensively cystic architecture, similar to multilocular cystic renal neoplasm of low malignant potential, and expressed cathepsin K and melanotic biomarker Melan A. This is the first time to correlate the MED15-TFE3 renal cell carcinoma with specific clinicopathologic features. We also report the first case of the corresponding mesenchymal neoplasm with MED15-TFE3 gene fusion. Additional novel TFE3 gene fusion partners, MATR3 and FUBP1, were identified. Cases with ASPSCR1-TFE3, SFPQ-TFE3, PRCC-TFE3, and NONO-TFE3 gene fusion showed a wide variability in morphologic features, including invasive tubulopapillary pattern simulating collecting duct carcinoma, extensive calcification and ossification, and overlapping and high columnar cells with nuclear grooves mimicking tall cell variant of papillary thyroid carcinoma. Furthermore, we respectively evaluated the ability of TFE3 immunohistochemistry, TFE3 FISH, RT-PCR, and RNA sequencing to subclassify Xp11 translocation-associated cancers. In summary, our study expands the list of TFE3 gene fusion partners and the clinicopathologic features of Xp11 translocation-associated cancers, and highlights the importance of subtyping Xp11 translocation-associated cancers combining morphology, immunohistochemistry, and multiple molecular techniques.

Novel gene fusion of PRCC-MITF defines a new member of MiT family translocation renal cell carcinoma: clinicopathological analysis and detection of the gene fusion by RNA sequencing and FISH.

AIMS: MITF, TFE3, TFEB and TFEC belong to the same microphthalmia-associated transcription factor family (MiT). Two transcription factors in this family have been identified in two unusual types of renal cell carcinoma (RCC): Xp11 translocation RCC harbouring TFE3 gene fusions and t(6;11) RCC harbouring a MALAT1-TFEB gene fusion. The 2016 World Health Organisation classification of renal neoplasia grouped these two neoplasms together under the category of MiT family translocation RCC. RCCs associated with the other two MiT family members, MITF and TFEC, have rarely been reported. Herein, we identify a case of MITF translocation RCC with the novel PRCC-MITF gene fusion by RNA sequencing. METHODS AND RESULTS: Histological examination of the present tumour showed typical features of MiT family translocation RCCs, overlapping with Xp11 translocation RCC and t(6;11) RCC. However, this tumour showed negative results in TFE3 and TFEB immunochemistry and split fluorescence in-situ hybridisation (FISH) assays. The other MiT family members, MITF and TFEC, were tested further immunochemically and also showed negative results. RNA sequencing and reverse transcription-polymerase chain reaction confirmed the presence of a PRCC-MITF gene fusion: a fusion of PRCC exon 5 to MITF exon 4. We then developed FISH assays covering MITF break-apart probes and PRCC-MITF fusion probes to detect the MITF gene rearrangement. CONCLUSIONS: This study both proves the recurring existence of MITF translocation RCC and expands the genotype spectrum of MiT family translocation RCCs.

EWSR1 rearrangement is present in a subset of myoepithelial tumors of salivary glands with variable morphology and does not correlate with clinical behavior.

To investigate that whether myoepithelial tumors of salivary glands (MTs) with EWSR1 rearrangement display distinctive morphological characteristics and whether EWSR1 detection aids to distinguish malignant myoepithelial tumors (MMTs) from benign myoepithelial tumors (BMTs) of salivary glands. We examined 37 cases of MTs, including 24 BMTs, 13 MMTs, by histological, immunohistochemical, and molecular analysis. All of 37 cases were immunoreactive for CKpan, and at least one myoepithelial marker. 26 of 37 cases of MTs were available to be analyzed for EWSR1 rearrangement, with the result that EWSR1 gene break was detected in 4 cases of 15 BMTs, and 4 cases of 11 MMTs. In addition, the 8 EWSR1-rearranged cases displayed not exactly similar morphological features, covering 4 clear-cell cases, 1 plasmacytoid-cell case, 1 spindle-cell case, 1 epithelioid-cell case, and 1 chordoid-cell case. Our study proposed that EWSR1 rearrangement was present in a subset of MTs, with variable morphological features. Moreover, the presence of EWSR1 rearrangement could not be a forceful evidence to distinguish MMTs from BBTs.

EGFR gene mutation in gastrointestinal stromal tumours.

AIMS: The aim of this study was to evaluate the mutation status of epidermal growth factor receptor (EGFR) in gastrointestinal stromal tumours (GISTs) and its association with various clinicopathological variables, as well as to discuss further the effects of EGFR mutations on tumour formation and progression. METHODS AND RESULTS: A well-characterized cohort of 323 GISTs, obtained between 2010 and 2015 from the surgical pathology files of at the Department of Pathology of the Nanjing Jinling Hospital, was screened for mutations in exons 19 and 21 of the EGFR gene. Patient clinical data and clinicopathological features were collected if available in the medical records. Among the 323 primary GISTs, we identified three cases (0.93%) of EGFR mutations; these mutations never occurred together with KIT, PDGFRα, KRAS or BRAF mutations. In two cases, tumour cells exhibited spindle cell morphology and, in one case, epithelioid cell morphology. Additionally, the morphology and immunophenotype of these three cases did not show significant differences compared to common GISTs. The clinical results in summary were that two cases of EGFR-mutated GISTs occurred in females and in the stomach. The mean age of EGFR-mutated cases was 54.33 years, and the follow-up data indicated that these tumours were low risk and exhibited low recurrence. CONCLUSIONS: We first established that GISTs carrying EGFR mutation are relatively benign tumours. Although EGFR mutations were rarely present in GIST, EGFR seems to play a significant role in the development and progression of GIST.

SFPQ/PSF-TFE3 renal cell carcinoma: a clinicopathologic study emphasizing extended morphology and reviewing the differences between SFPQ-TFE3 RCC and the corresponding mesenchymal neoplasm despite an identical gene fusion.

Xp11 translocation renal cell carcinoma (RCC) with SFPQ/PSF-TFE3 gene fusion is a rare epithelial tumor. Of note, the appearance of the gene fusion does not necessarily mean that it is renal cell carcinoma. The corresponding mesenchymal neoplasms, including Xp11 neoplasm with melanocytic differentiation, TFE3 rearrangement-associated perivascular epithelioid cell tumor (PEComa) and melanotic Xp11 translocation renal cancer, can also harbor the identical gene fusion. However, the differences between Xp11 translocation RCC and the corresponding mesenchymal neoplasm have only recently been described. Herein, we examined 5 additional cases of SFPQ-TFE3 RCCs using clinicopathologic, immunohistochemical, and molecular analyses. One tumor had the typical morphologic features of SFPQ-TFE3 RCC, whereas other 3 cases demonstrated the unusual morphologic features associated with pseudorosettes formation or clusters of smaller cells, mimicking TFEB RCC. The remaining one showed branching tubules and papillary structure composed of clear and eosinophilic tumor cells. Immunohistochemically, all 5 cases demonstrated moderate (2+) or strong (3+) positive staining for TFE3, PAX-8 and CD10, whereas no cases demonstrated TFEB, Cathepsin K, CA-IX, CK7, Melan-A, or HMB-45 expression. Genetically, the fusion transcripts were identified in 3 cases by reverse-transcription polymerase chain reaction (RT-PCR). On the basis of fluorescence in situ hybridization (FISH) analysis, all the cases were detected with SFPQ-TFE3 gene fusion. Clinical follow-up data were available for all the patients, and no one developed tumor recurrence, progression, or metastasis. We also review the differences between SFPQ-TFE3 RCC and the corresponding mesenchymal neoplasm despite the identical gene fusion. The presence of pseudorosettes also expands the known histological features of SFPQ-TFE3 RCC.

Xp11 Translocation Renal Cell Carcinomas (RCCs) With RBM10-TFE3 Gene Fusion Demonstrating Melanotic Features and Overlapping Morphology With t(6;11) RCC: Interest and Diagnostic Pitfall in Detecting a Paracentric Inversion of TFE3.

Xp11 translocation renal cell carcinomas (RCC) are characterized by several different translocations involving the TFE3 gene. Tumors with different specific gene fusions may have different clinicopathologic manifestations. Only 3 RBM10-TFE3 RCCs have been reported to date. Here, we added 4 cases of this rare type of tumors with clinicopathologic, immunohistochemical, molecular, and ultrastructural analyses. Most tumors had similar patterns with mixed architectures as follows: acinar, tubular and papillary patterns of epithelioid cells combined with sheets of small cells with "pseudorosette-like" architectures, mimicking the typical morphology of t(6;11) RCC. Cytoplasmic vacuolization, nuclear groove, and psammoma bodies were observed in most cases. Immunohistochemically, all 4 cases demonstrated moderate to strong immunoreactivity for TFE3, Cathepsin K, CD10, Ksp-cadherin, E-cadherin, P504S, RCC marker, PAX8 and vimentin, whereas negativity for TFEB, HMB45, and CK7. CKpan and Melan-A were at least focally expressed. The antibody to Ki-67 showed labeling of 3% to 8% (mean, 5%) of tumor cell nuclei. ;Of interest, several immunostainings demonstrated expression discrepancy in different histology patterns. RBM10-TFE3 fusion transcripts were identified in all cases by reverse transcription-polymerase chain reaction. By fluorescence in situ hybridization, all 4 cases showed unusual split signals with a distance <1 signal diameter (co-localized or subtle split signals) and usually had false-negative results. We also observed ultrastructures, including melanin pigment, nuclear groove, numerous glycogens, mitochondrion with areas of high electron density material, basement membrane material, and cell junctions with poor development. All 4 patients were alive with no evidence of recurrent disease. Our report adds to the known data regarding RBM10-TFE3 RCC.