Microsatellite instability has a positive prognostic impact on stage II colorectal cancer after complete resection: results from a large, consecutive Norwegian series.

BACKGROUND: Microsatellite instability (MSI) was suggested as a marker for good prognosis in colorectal cancer in 1993 and a systematic review from 2005 and a meta-analysis from 2010 support the initial observation. We here assess the prognostic impact and prevalence of MSI in different stages in a consecutive, population-based series from a single hospital in Oslo, Norway. PATIENTS AND METHODS: Of 1274 patients, 952 underwent major resection of which 805 were included in analyses of MSI prevalence and 613 with complete resection in analyses of outcome. Formalin-fixed tumor tissue was used for PCR-based MSI analyses. RESULTS: The overall prevalence of MSI was 14%, highest in females (19%) and in proximal colon cancer (29%). Five-year relapse-free survival (5-year RFS) was 67% and 55% (P = 0.030) in patients with MSI and MSS tumors, respectively, with the hazard ratio (HR) equal to 1.60 (P = 0.045) in multivariate analysis. The improved outcome was confined to stage II patients who had 5-year RFS of 74% and 56% respectively (P = 0.010), HR = 2.02 (P = 0.040). Examination of 12 or more lymph nodes was significantly associated with proximal tumor location (P < 0.001). CONCLUSIONS: MSI has an independent positive prognostic impact on stage II colorectal cancer patients after complete resection.

The APC gene I1307K variant is rare in Norwegian patients with familial and sporadic colorectal or breast cancer.

Recently, a T-to-A transversion creating an 8-base mononucleotide tract in the APC gene, resulting in substitution of lysine for isoleucine at codon 1307 (I1307K), was found in a subset of Ashkenazi Jews. This sequence variant was most frequent in colorectal cancer patients with a positive family history of colorectal cancer. To determine whether the I1307K variant plays a role in colorectal or breast cancer predisposition in the Norwegian population, we have analyzed blood samples from 210 colorectal cancer patients and 183 breast cancer patients by PCR and direct sequencing. Thirty-seven of the colorectal cancer patients had a positive family history of cancer. Among the breast cancer patients, 24 had a family history of colorectal cancer and 75 a family history of breast and/or ovarian cancer. Only one colorectal cancer patient who belonged to a Jewish family was found to carry the A variant. Our data show that the I1307K variant is rare in the Norwegian population and should not be viewed as a candidate for susceptibility testing for colorectal cancer.

Epigenetic and genetic features of 24 colon cancer cell lines.

Cell lines are invaluable biomedical research tools, and recent literature has emphasized the importance of genotype authentication and characterization. In the present study, 24 out of 27 cell line identities were confirmed by short tandem repeat profiling. The molecular phenotypes of the 24 colon cancer cell lines were examined, and microsatellite instability (MSI) and CpG island methylator phenotype (CIMP) were determined, using the Bethesda panel mononucleotide repeat loci and two epimarker panels, respectively. Furthermore, the BRAF, KRAS and PIK3CA oncogenes were analyzed for mutations in known hotspots, while the entire coding sequences of the PTEN and TP53 tumor suppressors were investigated. Nine cell lines showed MSI. Thirteen and nine cell lines were found to be CIMP positive, using the Issa panel and the Weisenberger et al. panel, respectively. The latter was found to be superior for CIMP classification of colon cancer cell lines. Seventeen cell lines harbored disrupting TP53 mutations. Altogether, 20/24 cell lines had the mitogen-activated protein kinase pathway activating mutually exclusive KRAS or BRAF mutations. PIK3CA and PTEN mutations leading to hyperactivation of the phosphoinositide 3-kinase/AKT pathway were observed in 13/24 cell lines. Interestingly, in four cell lines there were no mutations in neither BRAF, KRAS, PIK3CA nor in PTEN. In conclusion, this study presents molecular features of a large number of colon cancer cell lines to aid the selection of suitable in vitro models for descriptive and functional research.

Biallelic inactivation of TP53 rarely contributes to the development of malignant peripheral nerve sheath tumors.

About 10% of the patients with neurofibromatosis type 1 (NF1) develop malignant peripheral nerve sheath tumors (MPNSTs), accounting for half of all MPNST cases. Several nonrandom chromosomal aberrations have been found, but the target genes remain mostly unrecognized. Mutations in the NF1 and TP53 genes have been found in some MPNSTs, and recent data from mouse models support a synergistic effect of these two genes in the development of MPNST. In the present study, we have analyzed 16 MPNSTs, including 11 from patients with NF1 and 5 sporadic cases, for mutations in the coding sequence of the TP53 gene (exons 2-11). We applied denaturing gradient gel electrophoresis and modifications of this technique for analyses of 12 genomic fragments, followed by direct sequencing for identification of the mutated base(s). None of the MPNSTs revealed mutations. The detection of control mutants for each fragment analyzed, the high sensitivity of the technique, the detection of polymorphisms in some samples, and the high content of tumor tissue in the biopsies imply that false negatives are highly unlikely. Although we cannot exclude that deletions including large parts of the gene remain undetected by the mutation analyses, previous comparative genomic hybridization (CGH), cytogenetic banding analysis, and/or loss of heterozygosity studies on 14 of the cases included here had revealed 17p deletions in only three. We thus conclude that TP53 biallelic inactivation is rare in MPNST, and that the potential impact of an altered TP53 pathway on the malignant transformation of a neurofibroma into an MPNST may more frequently occur by changes in other components of that pathway.

Microsatellite instability in cervical and endometrial carcinomas.

Microsatellite instability has been found preferentially in tumours associated with the hereditary non-polyposis-colorectal-cancer (HNPCC) syndrome. This phenotype, manifested as new alleles at microsatellite loci, and often the result of a defective mismatch-repair gene, is seen as allelic mobility shifts during electrophoretic runs. We examined possible alterations at 8 dinucleotide loci mapping to 6 different chromosomes in endometrial cancers (n = 20) and cervical cancers (n = 82). Overall instability was found in 30% of the endometrial cancers and in 6% of the cervical cancers, including 3 (15%) and 2 (2%) tumours, respectively, unstable at more than one locus. In contrast to the endometrial cancer sub-group, the affected cervical cancers were characterized by one or two new alleles at one or few loci. By DNA ploidy measurements 5 diploid endometrial cancers were microsatellite-unstable vs. one diploid of 6 unaltered cases (p = 0.015; Fisher's exact test). Our data confirm that a sub-set of diploid sporadic endometrial cancers are characterized by a mutator phenotype similar to that found in colorectal cancer. In contrast, among cervical cancers, not characterized by the HNPCC-tumour spectrum, this mutator phenotype is seen infrequently, and positive cases appear to display only minor alterations.