Purpose-Microsatellite instability (MSI) is the hallmark of cancer with DNA mismatch repair (MMR) deficiency and underlies 20-30% of endometrial cancer. Some in vitro studies suggest that radiation effects are modulated by the MMR system, however, little is known about the relationship between MSI and radiation response. The aim of this study was to elucidate whether MSI predicts clinical outcome in radiation treated endometrioid endometrial cancer (EEC).Methods-We have studied a consecutive series of 93 patients with EEC treated with extrafacial hysterectomy and postoperative radiotherapy. The median clinical follow up of patients was of 138 months, with a maximum of 232 months. Five quasimonomorphic mononucleotide markers (BAT-25, BAT-26, NR21, NR24 and NR27) were used for MSI classification.Results-Twenty five patients (22%) were classified as MSI. Either in the whole series and in early stages (I and II), univariate analysis showed a significant association between MSI and a poorer 10-years local disease free (LDFS), disease free (DFS), and cancer-specific survival (CSS). In multivariate analysis, MSI was excluded from de final regression model in the whole series, but in early stages, MSI provided additional significant predictive information independent of traditional prognostic and predictive factors (age, stage, grade and vascular invasion) for DFS (HR, 3.25, 95%

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Microsatellite instability (MSI) and mutations in the PTEN gene are among the molecular alterations involved in endometrial carcinogenesis. There is conflicting information regarding to their role in this type of tumor. For this reason, we have studied both molecular lesions in a large population-based series of 205 patients with sporadic endometrial cancer. MSI was found in 41 (20.0%) of the tumors and PTEN mutations were found in 74 (36.1%). There were differences in genotype between tumors with and without MSI. Tumors with MSI showed both a higher frequency of PTEN mutations (58.5% vs. 30.4%) (p 5 0.002, Fisher's exact test) and a higher number of insertions or deletions (I/D) of one nucleotide within the mononucleotide tracts of the PTEN gene (45.8% vs. 11.4% out of all I/D, p 5 0.005). Conversely, G:C to A:T transitions in CpG dinucleotides were found mostly in microsatellite stable tumors (57.7% vs. 18.2% out of all single-base substitutions, p 5 0.037). Overall, 67.6% of tumors with mutated PTEN exhibited multiple mutations or allelic imbalance (AI). Multiple PTEN mutations in the same tumor were more frequent in tumors with MSI (60% vs. 25.7%); by contrast the presence of AI accompanying PTEN mutation was higher in microsatellite stable tumors (74.3% vs. 40%) (p 5 0.028). In addition, patients with both genetic alterations were diagnosed at more advanced stage of progression (54.2% for MSI vs. 20.0% for MSS, p 5 0.006), and exhibited a worse prognosis (hazard ratio [95% confidence interval]: 3.0 [1.1-13.1], p 5 0.034, log-rank test) than patients with only the PTEN gene mutated. Our data suggest that the DNA mismatch repair system status influences: (i) both the frequency and the mutational spectrum of PTEN; (ii) the nature of one of the hits that inactivate this tumor-suppressor gene; and (iii) the clinical condition and behavior of the patients. ' 2006 Wiley-Liss, Inc.Key words: microsatellite instability; PTEN mutation; endometrial cancer Microsatellite instability (MSI) is caused by defects in the DNA mismatch repair (MMR) system, either by mutations or by epigenetic events leading to gene silencing. 1,2 Tumors with MSI are characterized by a massive instability in simple repeated sequences and mutations in many cancer-related genes, particularly those with simple repeated sequences in their coding regions. [3][4][5][6][7] Tumors with MSI display a strong microsatellite mutator phenotype (MMP), which underlies a mutational pathway for gastrointestinal cancer that differs in genotype and phenotype from cancers with microsatellite stability (MSS).The MMP pathway for colon cancer possesses several peculiar characteristics in genotype. These tumors show a paradoxically low incidence of mutations affecting the prototypical cancer genes for colon cancer, namely the APC and p53 tumor suppressor genes and the K-ras oncogene. 3,[8][9][10][11] This low mutational incidence is also accompanied by a decreased incidence of loss of heterozygosity (LOH), 1,3,12 which is reflected at the cytogenetic level in freque...

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