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NUT carcinoma and thoracic SMARCA4‐deficient undifferentiated tumour are unique entities in the 5th edition of the World Health Organisation (WHO) Classification of Thoracic Tumours, whose definitions include molecular genetic abnormalities. These aggressive tumours require rapid work‐ups on biopsies, but a broad list of differential diagnoses poses challenges for practising pathologists. This review provides an update on their key clinicopathological and molecular characteristics, as well as controversies regarding tumour classification and diagnostic strategy. Phenotypical assessment plays a substantial role in diagnosis because recurrent and predictable clinicopathological findings exist, including robust immunohistochemical phenotypes. Accurate diagnosis is crucial for appropriate management and a clearer understanding of the disease. [ABSTRACT FROM AUTHOR]

Aims The aim of this study was to examine the status of Brahma (BRM), a key SWI/ SNF complex subunit, in clear cell renal cell carcinomas ( RCCs), and to analyse the histopathology, immunophenotype, molecular features and prognosis of the BRM-negative cases. Methods and results We identified 19 cases of grade 4 tumours lacking BRM expression among 625 clear cell RCCs. All 19 cases exhibited features of poor differentiation: 13 showed pure poorly differentiated morphology, while six were composite tumours with an admixed typical low-grade component. Besides negative BRM expression, the immunophenotype of these cases was similar to clear cell RCC. VHL gene mutations were identified in nine of the 19 patients (47%). Chromosome 3p deletion was detected in 11 of 13 poorly differentiated RCCs and both areas of five of five composite tumours. All poorly differentiated tumour areas showed polysomy of chromosome 3. No losses or gains of chromosome 3 were observed in low-grade tumour areas of five of five composite RCCs. Conclusions We have shown that loss of BRM expression is a common feature among poorly differentiated tumours in clear cell RCCs. We hypothesize that loss of BRM expression is involved in tumor de-differentiation in clear cell RCCs and may play an important role during tumour progression. [ABSTRACT FROM AUTHOR]

Aims Rhabdoid morphology resembling that of the aggressive paediatric rhabdoid tumours occurs in various malignancies usually lacking characteristic SMARCB1 ( INI1) loss. Little is known about the clinicopathological and molecular characteristics of the rhabdoid phenotype in gastrointestinal stromal tumours ( GISTs). Methods and results Six gastric rhabdoid GISTs were examined by immunohistochemistry, KIT and platelet-derived growth factor receptor-α gene ( PDGFRA) mutation analysis, and comparative genomic hybridization ( CGH). All tumours expressed KIT, PDGFRA, DOG-1, and SMARCB1 (two of six with a mosaic pattern). Five of six tumours harboured PDGFRA mutations (D842V in four; N659K in one), and one case was wild type for KIT/ PDGFRA and succinate dehydrogenase ( SDH) A-negative and SDHB-negative by immunohistochemistry. CGH revealed aberrations typical of GISTs (−1p, −14, and −22q in three, five, and three cases, respectively), with a mean of 1.7 aberrations in the epithelioid component and 2.7 in the rhabdoid component. None showed progression (mean follow-up of 25 months). Conclusions Rhabdoid gastric GISTs are associated with epithelioid morphology and PDGFRA mutations. They harbour CGH aberrations that are typical of ordinary GISTs in both tumour components. The presence of additional genetic alterations in the rhabdoid areas indicates evolution from the epithelioid components, and possible genetic and biological progression. On the basis of our series and previous reports, rhabdoid morphology in GISTs presumably does not imply aggressiveness. [ABSTRACT FROM AUTHOR]

Calderaro J, Moroch J, Pierron G, Pedeutour F, Grison C, Maillé P, Soyeux P, de la Taille A, Couturier J, Vieillefond A, Rousselet M C, Delattre O & Allory Y (2012) Histopathology 61, 428-435 SMARCB1/INI1 inactivation in renal medullary carcinoma Aims: Renal medullary carcinoma (RMC), a rare and highly aggressive tumour which occurs in patients with sickle-cell disease, shares many clinicopathological features with collecting duct carcinoma (CDC). The molecular mechanisms underlying RMC and CDC are mainly unknown, and there is ongoing debate about their status as distinct entities. Loss of expression of SMARCB1/INI1, a chromatin remodelling regulator and repressor of cyclin D1 transcription, has been reported recently in RMC. The aim of our study was to investigate if such loss of expression is specific for RMC. SMARCB1/INI1 genetic alterations and cyclin D1 expression were also studied. Methods and results: Using immunochemistry, neoplastic cells showed complete loss of SMARCB1/INI1 expression in all six cases of RMC but in only one of 22 cases of CDC. In two RMC cases investigated, comparative genomic hybridization demonstrated complete loss of one SMARCB1/INI1 allele, with no other genomic imbalances, and no mutations were found on the remaining allele. Cyclin D1 was expressed in all RMCs, suggesting that SMARCB1/INI1 inactivation may result in increased cyclin D1 transcription. Conclusions: The specific SMARCB1/INI1 inactivation observed in RMCs suggests that RMC and CDC are different entities. [ABSTRACT FROM AUTHOR]

Paediatric renal tumours represent a relatively common group of childhood solid neoplasms, in which both diagnosis and treatment are highly dependent on the histopathological findings. In addition to Wilms’ tumour (nephroblastoma), a number of specific distinct entities are now reported, including (congenital) mesoblastic nephroma, clear cell sarcoma of the kidney, rhabdoid tumour of the kidney, specific paediatric variants of renal cell carcinoma, and others such as renal primitive neuroectodermal tumour and desmoplastic small round cell tumour. Recent advances in both molecular biological findings and immunohistochemistry allow reliable diagnosis of most of these entities even on the basis of small needle biopsy specimens. This review highlights both the salient features important for the diagnostic pathologist reporting such cases, and areas in which either new classifications or major advances in diagnostic criteria have occurred in recent years. [ABSTRACT FROM AUTHOR]