Loss of heterozygosity at 12q14-15 often occurs in stage I soft tissue sarcomas and is associated with MDM2 amplification in tumors at various stages

The PTEN Tumor Suppressor Gene in Soft Tissue Sarcoma

Soft tissue sarcoma (STS) is a rare malignancy of mesenchymal origin classified into more than 50 different subtypes with distinct clinical and pathologic features. Despite the poor prognosis in the majority of patients, only modest improvements in treatment strategies have been achieved, largely due to the rarity and heterogeneity of these tumors. Therefore, the discovery of new prognostic and predictive biomarkers, together with new therapeutic targets, is of enormous interest. Phosphatase and tensin homolog (PTEN) is a well-known tumor suppressor that commonly loses its function via mutation, deletion, transcriptional silencing, or protein instability, and is frequently downregulated in distinct sarcoma subtypes. The loss of PTEN function has consequent alterations in important pathways implicated in cell proliferation, survival, migration, and genomic stability. PTEN can also interact with other tumor suppressors and oncogenic signaling pathways that have important implications for the pathogenesis in certain STSs. The aim of the present review is to summarize the biological significance of PTEN in STS and its potential role in the development of new therapeutic strategies.

Classification, molecular characterization, and the significance of pten alteration in leiomyosarcoma

Leiomyosarcoma is a malignant smooth muscle neoplasm with a complicated histopathologic classification scheme and marked differences in clinical behavior depending on the anatomic site of origin. Overlapping morphologic features of benign and borderline malignant smooth muscle neoplasms further complicate the diagnostic process. Likewise, deciphering the complex and heterogeneous patterns of genetic changes which occur in this cancer has been challenging. Preliminary studies suggest that reproducible molecular classification may be possible in the near future and new prognostic markers are emerging. Robust recapitulation of leiomyosarcoma in mice with conditional deletion of Pten in smooth muscle and the simultaneous discovery of a novel role for Pten in genomic stability provide a fresh perspective on the mechanism of leiomyosarcomagenesis and promise for therapeutic intervention.

MDM2 gene amplification in colorectal cancer is associated with disease progression at the primary site, but inversely correlated with distant metastasis

MDM2 is a crucial negative regulator of the TP53 tumor suppressor and almost 10% of human tumors exhibit MDM2 amplification. Although TP53 pathway perturbation has been extensively examined in colorectal cancer (CRC), only one previous report has evaluated MDM2 amplification in relation to clinicopathological factors. In that report, MDM2 amplification was shown to be associated with disease progression from Dukes' Stages A to D. In this study, we investigated MDM2 amplification by quantitative PCR and fluorescence in situ hybridization (FISH) together with the SNP309 genotypes, and analyzed the correlations with TP53 and KRAS mutations and clinicopathological features in 211 Japanese CRC patients. MDM2 amplification was detected in 8% of the specimens and its incidence was significantly higher in Dukes' stage C than in the combined earlier Stages A and B (P = 0.025). Unexpectedly, the incidence was significantly decreased in Stage D metastatic disease (P = 0.043). The copy number gain ranged from four to eight copies and was generally concordant with gain of centromere 12 using FISH analysis. Together with the results of centromere 1 FISH and TP53 copy number assessment, the MDM2 increment most likely resulted from chromosome 12 gain. The mechanism of the copy number gain and incidence in Dukes' Stage D differed considerably from the previous report. Ethnic or geographic factors could be responsible for these differences. Several promising therapeutic strategies targeting the TP53-MDM2 system are being developed. Further understanding of the significance of MDM2 and MDM2 amplification in CRC is required to facilitate personalized treatment for CRC patients.

Common genetic changes in leiomyosarcoma and gastrointestinal stromal tumour: implication for ataxia telangiectasia mutated involvement

Gastrointestinal stromal tumours (GISTs) are the most common mesenchymal tumours of the gastrointestinal tract. Formerly GISTs were commonly classified histologically as leiomyosarcomas; however, they are now known to arise from the interstitial cells of Cajal. Majority of GISTs overexpress KIT and have characteristic mutations within the gene, which are the targets of drug treatment with tyrosine kinase inhibitors. Leiomyosarcoma is a malignant tumour of smooth muscle differentiation and falls into a group of sarcomas that show complex karyotypic changes with no consistent recurrent genetic abnormality. We have used comparative genomic hybridization in combination with fluorescence in situ hybridization to determine genetic differences between the tumour types. We found leiomyosarcomas and GISTs share common regions of chromosomal 13q and 11q imbalance, in addition to more specific 1p and 8p losses in leiomyosarcoma and 15q and 22q losses in GISTs. More importantly, we have shown for the first time a deletion in the ataxia telangiectasia mutated (ATM) gene locus with decreased/absent expression of ATM protein, and amplification in the region 13q21-q32 in both tumour types, suggesting both regions may play a role in leiomyosarcoma and GIST biology.

Regulating the p53 pathway: in vitro hypotheses, in vivo veritas

Mutations in TP53, the gene that encodes the tumour suppressor p53, are found in 50% of human cancers, and increased levels of its negative regulators MDM2 and MDM4 (also known as MDMX) downregulate p53 function in many of the rest. Understanding p53 regulation remains a crucial goal to design broadly applicable anticancer strategies based on this pathway. This Review of in vitro studies, human tumour data and recent mouse models shows that p53 post-translational modifications have modulatory roles, and MDM2 and MDM4 have more profound roles for regulating p53. Importantly, MDM4 emerges as an independent target for drug development, as its inactivation is crucial for full p53 activation.