World Health Organization Classification of Tumours

MicroRNA (miRNA ) alterations are involved in the initiation and progression of human cancer. The causes of the widespread differential expression of miRNA genes in malignant compared with normal cells can be explained by the location of these genes in cancer-associated genomic regions, by epigenetic mechanisms and by alterations in the miRNA processing machinery. MiRNA-expression profiling of human tumours has identified signatures associated with diagnosis, staging, progression, prognosis and response to treatment. In addition, profiling has been exploited to identify miRNA genes that might represent downstream targets of activated oncogenic pathways, or that target protein- coding genes involved in cancer.

MicroRNA signatures in human cancers

MicroRNA (miRNA) alterations are involved in the initiation and progression of human cancer. The causes of the widespread differential expression of miRNA genes in malignant compared with normal cells can be explained by the location of these genes in cancer-associated genomic regions, by epigenetic mechanisms and by alterations in the miRNA processing machinery. MiRNA-expression profiling of human tumours has identified signatures associated with diagnosis, staging, progression, prognosis and response to treatment. In addition, profiling has been exploited to identify miRNA genes that might represent downstream targets of activated oncogenic pathways, or that target protein- coding genes involved in cancer.

I MicroRNAs (miRNAs) are an abundant class of small non-protein-coding RNAs that function as negative gene regulators. They regulate diverse biological processes, and bioinformatic data indicates that each miRNA can control hundreds of gene targets, underscoring the potential influence of miRNAs on almost every genetic pathway. Recent evidence has shown that miRNA mutations or mis-expression correlate with various human cancers and indicates that miRNAs can function as tumour suppressors and oncogenes. miRNAs have been shown to repress the expression of important cancer-related genes and might prove useful in the diagnosis and treatment of cancer.

Oncomirs : microRNAs with a role in cancer

MicroRNAs (miRNAs) are an abundant class of small non-protein-coding RNAs that function as negative gene regulators They regulate diverse biological processes, and bioinformatic data indicates that each miRNA can control hundreds of gene targets, underscoring the potential influence of miRNAs on almost every genetic pathway Recent evidence has shown that miRNA mutations or mis-expression correlate with various human cancers and indicates that miRNAs can function as tumour suppressors and oncogenes miRNAs have been shown to repress the expression of important cancer-related genes and might prove useful in the diagnosis and treatment of cancer

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Oncomirs — microRNAs with a role in cancer

Mucous Gland Adenoma

Lymphoepithelioma-Like Carcinoma

Idiopathic Sclerosing Mediastinitis

Squamous Cell Carcinoma

Primary thymic epithelial neoplasms represent the most common type of tumors of the anterior mediastinum. These tumors have been a source of major controversy over the years due to their difficulties for histopathologic typing and often unpredictable biologic behavior. Unlike malignant epithelial neoplasms arising at other organs, these tumors were felt for many years to be unsuitable for histologic grading. In fact, the latest WHO schema for the classification of thymic epithelial neoplasms does not mention grading for these tumors at all. More recent observations, however, have demonstrated that thymic epithelial neoplasms form part of a continuous spectrum of lesions that may closely resemble their parent organ at the one end or be very poorly differentiated at the other extreme [1]. Based on these observations, a novel conceptual approach was recently introduced for the classification of thymic epithelial neoplasms that is based on the histologic degree of differentiation of the lesions [2]. The histologic grading of these tumors is based on the premise that these lesions can range from well-differentiated to moderately differentiated to poorly differentiated neoplasms. This is supported by the observation of tumor progression in thymoma whereby recurrences show transformation of a low-grade histologic type to that of a higher-grade histology [3]. The degree of differentiation in any given tumor will depend on the presence or absence of the organotypical features of differentiation of the thymus and on the degree of cytological atypia displayed by the tumor cells (see Table 4.1).

Saul Suster

Papers

Mucous Gland Adenoma

Lymphoepithelioma-Like Carcinoma

Idiopathic Sclerosing Mediastinitis

Squamous Cell Carcinoma

Tumors of the Thymus