Cytogenetic abnormalities in solid tumours of childhood

Cytogenetic abnormalities have been described in a number of solid tumours of childhood. In many paediatric sarcomas and lymphomas, the demonstration of specific translocations has led to the identification of fusion genes of diagnostic, prognostic and potential therapeutic importance. These characteristic translocations are frequently accompanied by secondary karyotypic changes that may contribute to neoplastic progression. In paediatric solid tumours where no primary cytogenetic abnormality has been identified, numerous recurring aberrations are observed that often correlate with prognosis. In this review, karyotypic abnormalities detected by both conventional and recent molecular cytogenetic approaches in the most common solid tumours of childhood — neuroblastoma, Wilms' tumour, rhabdomyosarcoma, Ewing's tumour and certain lymphomas — are described. Characterization of these aberrations will not only increase our understanding of tumourigenesis, but will also provide unique diagnostic and prognostic markers for the clinic.     

Sarcomas: genetics, signalling, and cellular origins. Part 1: The fellowship of TET

Sarcomas comprise some of the most aggressive solid tumours that, for the most part, respond poorly to chemo- and radiation therapy and are associated with a sombre prognosis when surgical removal cannot be performed or is incomplete. Partly because of their lower frequency, sarcomas have not been studied as intensively as carcinomas and haematopoietic malignancies, and the molecular mechanisms that underlie their pathogenesis are only beginning to be understood. Even more enigmatic is the identity of the primary cells from which these tumours originate. Over the past 25 years, however, several non-random chromosomal translocations have been found to be associated with defined sarcomas. Each of these translocations generates a fusion gene believed to be directly related to the pathogenesis of the sarcoma in which it is expressed. The corresponding fusion proteins provide a unique tool not only to study the process of sarcoma development, but also to identify cells that are permissive for their putative oncogenic properties. This is the first of two reviews that cover the mechanisms whereby specific fusion/mutant gene products participate in sarcoma development and the cellular context that may provide the necessary permissiveness for their expression and oncogenicity. Part 1 of the review focuses on sarcomas that express fusion genes containing TET gene family products, including EWSR1, TLS/FUS, and TAFII68. Part 2 (J Pathol 2007; DOI: 10.1002/path.2008) summarizes our current understanding of the genetic and cellular origins of sarcomas expressing fusion genes exclusive of TET family members; it also covers soft tissue malignancies harbouring specific mutations in RTK-encoding genes, the prototype of which are gastrointestinal stromal tumours (GIST).     

The role of genetic testing in soft tissue sarcoma

Soft tissue tumours represent a heterogeneous group of mesenchymal lesions and their classification continues to evolve as a result of incorporating advances in cytogenetic and molecular techniques. In the last decade traditional diagnostic approaches were supplemented with a significant number of reliable molecular diagnostic tools, detecting tumour type-specific genetic alterations. In addition, the successful application of some of these techniques to formalin-fixed paraffin-embedded tissue made it possible to subject a broader range of clinical material to molecular analysis. Thus, molecular genetics has already become an integral part of the work-up in some tumours, such as paediatric small blue round cell tumours, which demonstrate characteristic translocations. Several lines of evidence suggest that sarcomas can be divided into two major genetic groups: (i) sarcomas with specific genetic alterations and usually simple karyotypes, such as reciprocal chromosomal translocations (e.g. FUS-DDIT3 in myxoid liposarcoma) and specific oncogenic mutations (e.g. KIT mutation in gastrointestinal stromal tumours); and (i) sarcomas with non-specific genetic alterations and complex unbalanced karyotypes. Some of these genetic abnormalities, including chromosomal numerical changes, translocations, gene amplifications or large deletions can be apparent at the cytogenetic level (karyotyping, fluorescence in situ hybridization), while others, such as small deletions, insertions or point mutations, require molecular genetic techniques (polymerase chain reaction and sequence analysis). This review focuses on the applicability of genetic testing in the diagnosis and prognosis of soft tissue sarcomas, and gives a realistic appraisal of the ancillary role of molecular techniques, including its advantages and limitations.     

Biological continuum of benign, atypical, and malignant mesenchymal neoplasms - does it exist?

The characterization of specific cytogenetic and molecular abnormalities in benign and malignant soft tissue tumours has increased our understanding and knowledge of the biology of these rare neoplasms in recent years and has led to the modification of a number of traditional classification schemes. Contrary to popular belief, it is reasonable to propose that there exists a molecular, genetic, and morphological continuum of benign, atypical, and malignant mesenchymal neoplasms. The identification of characteristic molecular changes in benign lipomas, lipomas with minimal atypia, and atypical lipomatous tumours, well-differentiated liposarcomas supports the hypothesis of a stepwise process in the pathogenesis of these neoplasms. Not only are these findings important for our understanding of the biology of soft tissue tumours, but they also may increase diagnostic and prognostic accuracy.     

Chromosome translocations in sarcomas and the analysis of paraffin-embedded material

The identification of specific chromosome translocations in various sarcomas and the elucidation of their molecular consequences has raised the possibility of detecting their presence for diagnostic and prognostic purposes in a manner analogous to the haematological malignancies. However, it is important to correlate particular translocations, and also other genetic aberrations, with current histological diagnoses and the behaviour of tumours, in order to assess the potential benefits, if any, of identifying rearrangements. Recent developments which enable specific translocations to be identified in archival material are likely to play an increasing role in the assessment and, eventually, the management of patients with sarcomas. © 1998 John Wiley & Sons, Ltd.     

Recent developments in uterine mesenchymal neoplasms

Smooth muscle and endometrial stromal tumours represent the two most common uterine mesenchymal neoplasms that may present diagnostic dilemmas for the practising surgical pathologist. Recent changes in morphological and staging criteria, as well as the discovery of new immunohistochemical markers, have improved the diagnosis and classification of these tumours. We highlight the difficulty in distinguishing tumour cell necrosis from infarct‐type necrosis and the limited utility of p16 immunohistochemical expression in the diagnosis of leiomyosarcoma. We also discuss the controversial use of mitotic activity and necrosis as prognostic factors in endometrial stromal sarcomas. Emerging genetic information has also greatly expanded our understanding of ‘sarcomagenesis’ in both tumour types and may provide insight into potential therapeutic targets for the treatment of leiomyosarcoma and endometrial stromal sarcomas, harboring MED12 (mediator complex subunit 12) mutations and recurrent gene rearrangements, respectively. In this review, we discuss the core updates in the diagnosis and classification of uterine leiomyosarcomas and endometrial stromal sarcomas, highlighting new and important molecular genetic findings that may drive pathogenesis.     

A current perspective on the role for molecular studies in soft tissue tumor pathology

Soft tissue sarcomas represent an heterogenous group of malignancies. They represent a diagnostic challenge, and their accurate classification impact over treatment options. Sarcomas, similarly to hematologic neoplasm, often harbor relatively specific genetic aberrations, the recognition of which can be used to improved diagnostic accuracy. This review will focus on the clinical relevance of molecular analysis in soft tissue sarcomas, trying to elucidate its role as a diagnostic tool as well as a potential prognostic/predictive marker.     

Pathological and molecular features of adrenocortical carcinoma: an update

The pathological diagnosis of adrenocortical carcinoma (ACC), which is based on gross and microscopic criteria, is subjective. None of the features are absolutely indicative of malignancy, although their combination in a scoring system may correctly identify ACC. The Weiss system, which is currently the most popular, combines nine morphological parameters, of which three are structural ("dark" cytoplasm, diffuse architecture, necrosis), three are cytological (atypia, mitotic count, atypical mitotic figures) and three are related to invasion (of sinusoids, veins and tumour capsule). Although there are strictly defined criteria for each feature, some are straightforward and objective, while others are potentially more problematic (diffuse architecture, necrosis, sinusoidal, venous and capsular invasions). The classification of oncocytic and paediatric adrenocortical tumours is even more challenging, as not all of the above morphological parameters are predictors of malignancy in these tumour types. As an alternative to the morphological approach, a wide array of chromosomal, genetic, molecular and immunohistochemical markers have been tested in ACC to identify reliable diagnostic and prognostic factors. Genetic and epigenetic alterations of p53, IGF-2 and molecules involved in cancer cell invasive properties seem the most promising. These molecular markers may not only play a role in the biology of these tumours and have prognostic implications, but may also be used as potential targets for treatment. However, these markers are not sufficiently sensitive and specific to replace conventional morphological criteria.     

Cytogenetic and molecular aberrations in endometrial stromal tumors

Endometrial stromal tumors (ESTs) are rare uterine mesenchymal tumors, comprising <10% of all uterine mesenchymal neoplasms. The latest World Health Organization classification divides endometrial stromal tumors into 3 categories based on morphologic features: endometrial stromal nodule (ESN), low-grade endometrial stromal sarcoma, and undifferentiated endometrial sarcoma. Specific cytogenetic aberrations and molecular genetic alterations have recently been identified in endometrial stromal tumors, providing insights into their molecular biology, potential diagnostic markers, and possible therapeutic targets. Currently, recurrent chromosomal rearrangements resulting in gene fusion play a substantive role in the pathogenesis of endometrial stromal nodules, endometrial stromal sarcomas, and a small subset of undifferentiated endometrial sarcomas. Loss of heterozygosity of tumor suppressor genes and deregulation of the Wnt signaling pathway have also been implicated in EST tumorigenesis. In this review, we summarize the recent advances in the molecular pathology of endometrial stromal tumors.     

Histopathological features of pretreatment neuroblastoma are of limited clinical significance following adjustment for clinical and biological marker status

Neuroblastic tumours are morphologically classified into broad categories according to defined criteria, with further histopathological features described which may provide prognostic information, such as calcification, mitotic rate and the mitoses-karyorrhexis index; these may be combined with patient age and other factors to indicate high-risk and low-risk groups. However, recently, a range of biological molecular markers have proved to be of major prognostic importance in neuroblastic tumours, including MYCN amplification, 1p deletion, and 17q gain. It is therefore hypothesised that traditional histopathological features are now of limited clinical significance after adjustment for known clinical and biological pregnostic markers. Evidence to evaluate this hypothesis was obtained via a literature search to identify studies reporting on prognostic significance of histopathological features in multivariate analysis after adjustment for biological marker status. Thirteen studies were included of which four (1642 subjects) reported an independent effect of histopathological findings, whereas nine (2385 subjects) reported no significant independent effect. All four studies examining both MYCN and other markers such as 1p, 11q or 17q status, reported no significant independent effect of histological parameters. Histopathological diagnosis remains the gold standard for the diagnosis and evaluation of paediatric tumours but in the evolving era of molecular evaluation of tumours, the role of traditional morphological assessments is likely to become increasingly obsolete, and diagnostic paediatric pathology departments must respond to the changing understanding of the biological basis of childhood malignancies towards routinely providing both diagnostic and molecular prognostic data from these small samples.     

The molecular genetic profile of neuroblastoma

Neuroblastoma is the most common extracranial solid tumour of childhood and is characterized by a remarkable heterogeneity in histology and molecular biology that is reflected in its clinical outcome. Unlike many paediatric malignancies, molecular genetic results are used for prognosis rather than diagnosis. The molecular genetic changes in neuroblastoma are reviewed and summarized. Some genetic changes (ploidy, MYCN copy number, 11q deletion) are used for risk stratification that determines patient treatment. Other genetic changes (e.g 1p deletion, 17q gain) are strong prognostic indicators for an unfavourable outcome. Mutations in individual genes (e.g ALK) are becoming important in personalizing therapy as more agents become available for ‘druggable’ targets. Newer genetic data related to miRNA expression and genome-wide association screening offer the promise of new avenues to pursue to improve the dismal outcome in high risk patients with neuroblastoma.     

Ewing family tumours: a paediatric perspective

Sarcomas are malignant tumours of the connective tissues and are proportionately much more common in children than in adults. The Ewing family of tumours (EFT) is a group of sarcomas sharing rearrangement of the EWSR1 gene on 22q12, and include Ewing sarcoma/primitive neuroectodermal tumour, desmoplastic small round cell tumour, angiomatoid fibrous histiocytoma and clear cell sarcoma. Other tumours harbouring EWSR1 rearrangements include myoepithelial tumours, myxoid liposarcoma and extraskeletal chondrosarcoma. In addition, a group of Ewing-like primitive round cell sarcomas have been recently described in a paediatric population, further expanding the list of EFT. This review will focus on the histopathological, immunohistochemical and molecular genetic features of EFT, with an emphasis on those predominantly occurring in the paediatric population.     

Sarcomas: genetics, signalling, and cellular origins. Part 2: TET-independent fusion proteins and receptor tyrosine kinase mutations

Although the mechanisms that underlie sarcoma development are still poorly understood, the identification of non-random chromosomal translocations and receptor tyrosine kinase mutations associated with defined sarcoma types has provided new insight into the pathogenesis of these tumours. In Part 1 of the review (J Pathol 2007;213:4-20), we addressed sarcomas that express fusion genes containing TET gene family products. Part 2 of the review summarizes our current understanding of the implications of fusion genes that do not contain TET family members in sarcoma development, as well as that of specific mutations in genes encoding receptor tyrosine kinases (RTKs). The final section will serve as a summary of both reviews and will attempt to provide a synthesis of some of the emerging principles of sarcomagenesis.     

Soft tissue sarcomas with non-EWS translocations: molecular genetic features and pathologic and clinical correlations

Many soft tissue sarcoma subtypes have consistent chromosomal translocations with novel fusion genes, which result in disordered cellular function. The microscopic appearances, immunophenotype and behaviour of such tumours relate to the genetic events to a variable extent. This paper reviews the molecular pathology and related morphological and clinical features of sarcomas with non-EWS translocations. These include synovial sarcoma, alveolar rhabdomyosarcoma, alveolar soft part sarcoma, dermatofibrosarcoma protuberans, low-grade fibromyxoid sarcoma, infantile fibrosarcoma and inflammatory myofibroblastic tumour.     

Fibroepithelial lesions of the breast: A review of recurring diagnostic issues

Breast fibroepithelial lesions, which are composed of biphasic epithelial and stromal proliferations, comprise the fascinating spectrum of fibroadenomas and phyllodes tumours. Common difficulties surrounding their diagnosis include distinguishing between cellular fibroadenomas and benign phyllodes tumours, grading phyllodes tumours, classifying fibroepithelial lesions in paediatric patients, and handling surgical margins. Recent molecular advances have provided insights into the pathogenesis of fibroepithelial lesions and may offer diagnostic, prognostic, and therapeutic information. In this review, we briefly revisit the pathological features of fibroadenomas and phyllodes tumours, discuss common diagnostic dilemmas and management implications, and examine their key molecular characteristics.     

Molecular cytogenetics of cutaneous melanocytic lesions – diagnostic,prognostic and therapeutic aspects

Blokx W A M, van Dijk M C R F & Ruiter D J
(2010) Histopathology 56 , 121–132
Molecular cytogenetics of cutaneous melanocytic lesions – diagnostic, prognostic and therapeutic aspects This review intends to update current knowledge regarding molecular cytogenetics in melanocytic tumours with a focus on cutaneous melanocytic lesions. Advantages and limitations of diverse, already established methods, such as (fluorescence) in situ hybridization and mutation analysis, to detect these cytogenetic alterations in melanocytic tumours are described. In addition, the potential value of more novel techniques such as multiplex ligation‐dependent probe amplification is pointed out. This review demonstrates that at present cytogenetics has mainly increased our understanding of the pathogenesis of melanocytic tumours, with an important role for activation of the mitogen‐activated protein kinase (MAPK) signalling pathway in the initiation of melanocytic tumours. Mutations in BRAF (in common naevocellular naevi), NRAS (congenital naevi), HRAS (Spitz naevi) and GNAQ (blue naevi) can all cause MAPK activation. All these mutations seem early events in the development of melanocytic tumours, but by themselves are insufficient to cause progression towards melanoma. Additional molecular alterations are implicated in progression towards melanoma, with different genetic alterations in melanomas at different sites and with varying levels of sun exposure. This genetic heterogeneity in distinct types of naevi and melanomas can be used for the development of molecular tests for diagnostic purposes. However, at the moment only few molecular tests have become of diagnostic value and are performed in daily routine practice. This is caused by lack of large prospective studies on the diagnostic value of molecular tests including follow‐up, and by the low prevalence of certain molecular alterations. For the future we foresee an increasing role for cytogenetics in the treatment of melanoma patients with the increasing availability of targeted therapy. Potential targets for metastatic melanoma include genes involved in the MAPK pathway, such as BRAF and RAS. More recently, KIT has emerged as a potential target in melanoma patients. These targeted treatments all need careful evaluation, but might be a promising adjunct for treatment of metastatic melanoma patients, in which other therapies have not brought important survival advantages yet.