Multi-omics characterization and validation of MSI-related molecular features across multiple malignancies.

HEADINGS AIMS: To establish a microsatellite instability (MSI) predictive model in pan-cancer and compare the multi-omics characterization of MSI-related molecular features. MATERIALS AND METHODS: We established a 15-gene signature for predicting MSI status and performed a systematic assessment of MSI-related molecular features including gene and miRNA expression, DNA methylation, and somatic mutation, in approximately 10,000 patients across 30 cancer types from The Cancer Genome Atlas, Gene Expression Omnibus database, and our institution. Then we identified common MSI-associated dysregulated molecular features across six cancers and explored their mutual interfering relationships and the drug sensitivity. KEY FINDINGS: we demonstrated the model's high prediction performance and found the samples with high-MSI were mainly distributed in six cancers: BRCA, COAD, LUAD, LIHC, STAD, and UCEC. We found RPL22L1 was up-regulated in the high-MSI group of 5/6 cancer types. CYP27A1 and RAI2 were down-regulated in 4/6 cancer types. More than 20 miRNAs and 39 DMGs were found up-regulated in MSI-H at least three cancers. We discovered some drugs, including OSI-027 and AZD8055 had a higher sensitivity in the high MSI-score group. Functional enrichment analysis revealed the correlation between MSI score and APM score, HLA score, or glycolysis score. The complicated regulatory mechanism of tumor MSI status in multiple dimensions was explored by an integrated analysis of the correlations among MSI-related genes, miRNAs, methylation, and drug response data. SIGNIFICANCE: Our pan-cancer study provides a valuable predictive model and a comprehensive atlas of tumor MSI, which may guide more precise and personalized therapeutic strategies for tumor patients.

The Clinical Significance of Microsatellite Instability in Precision Treatment.

The recent years have seen the high heterogeneity of colorectal cancer (CRC) receiving increasing attention and being revealed step by step. Microsatellite instability (MSI), characterized by the dysfunction of mismatch repair gene, plays an important role in the heterogeneity of colorectal cancer. MSI status can be identified by immunohistochemistry for MMR protein such as MLH1, MSH2, PMS2, and MSH6 or PCR-based array for MMR gene. Recent studies have revealed MSI status is the only biomarker that can be used to select patients with high-risk stage II colon cancer for adjuvant chemotherapy. Furthermore, it always indicated better stage-adjusted survival when compared with microsatellite stable (MSS) tumors. For immunotherapy, patients with MSI tumors exhibited significant response to anti-PD-1 inhibitors after the failure to conventional therapy. In this chapter, we discuss the detection methods of MSI, the prognostic value of MSI, and its clinical guiding value in the management of precision therapy.

A Short Tandem Repeat-Enriched RNA Assembles a Nuclear Compartment to Control Alternative Splicing and Promote Cell Survival.

Functions of many long noncoding RNAs (lncRNAs) depend on their ability to interact with multiple copies of specific RNA-binding proteins (RBPs). Here, we devised a workflow combining bioinformatics and experimental validation steps to systematically identify RNAs capable of multivalent RBP recruitment. This uncovered a number of previously unknown transcripts encoding high-density RBP recognition arrays within genetically normal short tandem repeats. We show that a top-scoring hit in this screen, lncRNA PNCTR, contains hundreds of pyrimidine tract-binding protein (PTBP1)-specific motifs allowing it to sequester a substantial fraction of PTBP1 in a nuclear body called perinucleolar compartment. Importantly, PNCTR is markedly overexpressed in a variety of cancer cells and its downregulation is sufficient to induce programmed cell death at least in part by stimulating PTBP1 splicing regulation activity. This work expands our understanding of the repeat-containing fraction of the human genome and illuminates a novel mechanism driving malignant transformation of cancer cells.

Disease-Associated Short Tandem Repeats Co-localize with Chromatin Domain Boundaries.

More than 25 inherited human disorders are caused by the unstable expansion of repetitive DNA sequences termed short tandem repeats (STRs). A fundamental unresolved question is why some STRs are susceptible to pathologic expansion, whereas thousands of repeat tracts across the human genome are relatively stable. Here, we discover that nearly all disease-associated STRs (daSTRs) are located at boundaries demarcating 3D chromatin domains. We identify a subset of boundaries with markedly higher CpG island density compared to the rest of the genome. daSTRs specifically localize to ultra-high-density CpG island boundaries, suggesting they might be hotspots for epigenetic misregulation or topological disruption linked to STR expansion. Fragile X syndrome patients exhibit severe boundary disruption in a manner that correlates with local loss of CTCF occupancy and the degree of FMR1 silencing. Our data uncover higher-order chromatin architecture as a new dimension in understanding repeat expansion disorders.

The proline-arginine repeat protein linked to C9-ALS/FTD causes neuronal toxicity by inhibiting the DEAD-box RNA helicase-mediated ribosome biogenesis.

A GGGGCC repeat expansion in the C9ORF72 gene has been identified as the most common genetic cause of amyotrophic lateral sclerosis and frontotemporal dementia. The repeat expansion undergoes unconventional translation to produce dipeptide repeat (DPR) proteins. Although it has been reported that DPR proteins cause neurotoxicity, the underlying mechanism has not been fully elucidated. In this study, we have first confirmed that proline-arginine repeat protein (poly-PR) reduces levels of ribosomal RNA and causes neurotoxicity and found that the poly-PR-induced neurotoxicity is repressed by the acceleration of ribosomal RNA synthesis. These results suggest that the poly-PR-induced inhibition of ribosome biogenesis contributes to the poly-PR-induced neurotoxicity. We have further identified DEAD-box RNA helicases as poly-PR-binding proteins, the functions of which are inhibited by poly-PR. The enforced reduction in the expression of DEAD-box RNA helicases causes impairment of ribosome biogenesis and neuronal cell death. These results together suggest that poly-PR causes neurotoxicity by inhibiting the DEAD-box RNA helicase-mediated ribosome biogenesis.

A single center's approach to discriminating donor versus host origin of renal neoplasia in the allograft kidney.

Renal cell carcinoma (RCC) in the allograft of kidney transplant recipient (KTR) patients is rare and may represent a de novo process arising from the transplanted organ or metastasis from a clinically undetectable host primary. Determination of host versus donor origin is important for staging and management. We report our experience utilizing Penta-C (PC) and Penta-D (PD) short-tandem repeat (STR) microsatellite analysis to discriminate between host and donor origin of RCC identified in renal allografts. We identified 5 KTR patients with RCC in the allograft kidney. The PC and PD microsatellite analysis was applied to tumor, host, and donor formalin-fixed, paraffin-embedded tissue sections and/or fresh blood leukocytes to identify the origin of the neoplastic cells. The PC and PD microsatellite alleles were robustly amplified in all samples. Each case showed one or more informative alleles indicating that the neoplastic cells originate from donor tissue. Allele frequency data indicate that by using both PC and PD markers, we will be able to discriminate between host and donor cell of origin in over 99% of cases. The PC and PD microsatellite analysis is a convenient, robust, and efficient strategy to determine donor versus host origin or RCC in transplant kidney specimens.

Evaluation of a new panel of six mononucleotide repeat markers for the detection of DNA mismatch repair-deficient tumours.

BACKGROUND: Microsatellite instability (MSI) is a molecular phenotype due to defective DNA mismatch repair (MMR) system. It is used to predict outcome of colorectal tumours and to screen tumours for Lynch syndrome (LS). A pentaplex panel composed of five mononucleotide markers has been largely recommended for determination of the MSI status. However, its sensitivity may be taken in default in occasional situations. The aim of the study was to optimise this panel for the detection of MSI. METHODS: We developed an assay allowing co-amplification of six mononucleotide repeat markers (BAT25, BAT26, BAT40, NR21, NR22, NR27) and one polymorphic dinucleotide marker (D3S1260) in a single reaction. Performances of the new panel were evaluated on a cohort of patients suspected of LS. RESULTS: We demonstrate that our assay is technically as easy to use as the pentaplex assay. The hexaplex panel shows similar performances for the identification of colorectal and non-MSH6-deficient tumours. On the other hand, the hexaplex panel has higher sensitivity for the identification of MSH6-deficient tumours (94.7% vs 84.2%) and MMR-deficient tumours other than colorectal cancer (92.9% vs 85.7%). CONCLUSION: The hexaplex panel could thus be an attractive alternative to the pentaplex panel for the identification of patients with LS.

Outcome and status of microsatellite stability in Japanese atomic bomb survivors with early gastric carcinoma.

BACKGROUND: In the decade after the 1945 atomic bombing of Hiroshima, a high incidence of leukemia was observed among atomic bomb survivors. However, the incidence of other cancers gradually increased, while that of leukemia decreased after this period. We evaluated the clinical outcome of early gastric cancer and microsatellite stability over a long-term period in atomic bomb survivors. METHODS: The results of surgical treatment for early gastric cancer were reviewed for 117 atomic bomb survivors and 394 control patients between 1995 and 2006. In addition, immunohistochemical staining for hMSH2 and hMLH1 expression was performed to evaluate the status of microsatellite stability in 57 atomic bomb survivors and 82 control patients. RESULTS: The long-term survival rate for early gastric cancer in atomic bomb survivors was significantly lower than that in control patients (p < 0.01). Multivariable analysis revealed that age and sex were significant and independent prognostic factors for early gastric cancer. Defective hMSH2 and/or hMLH1 expression was also significantly higher in survivors than in control patients (p < 0.001). Logistic regression analysis revealed that atomic bomb survivorship was related to defective hMSH2 and/or hMLH1 expression. CONCLUSIONS: The prognosis of early gastric cancer in atomic bomb survivors was poor and was related to age and sex, rather than to being an atomic bomb survivor. Furthermore, a higher rate of defective hMSH2 and/or hMLH1 expression was observed in the survivors.

Carcinoembryonic antigen interacts with TGF-{beta} receptor and inhibits TGF-{beta} signaling in colorectal cancers.

As a tumor marker for colorectal cancers, carcinoembryonic antigen (CEA) enhances the metastatic potential of cancer cells. CEA functions as an intercellular adhesion molecule and is upregulated in a wide variety of human cancers. However, the molecular mechanisms by which CEA mediates metastasis remain to be understood. Transforming growth factor-ß (TGF-ß) signaling regulates both tumor suppression and metastasis, and also contributes to the stimulation of CEA transcription and secretion in colorectal cancer cells. However, it remains unknown whether CEA, in turn, influences TGF-ß functions and if a regulatory cross-talk exists between CEA and the TGF-ß signaling pathway. Here, we report that CEA directly interacts with TGF-ß receptor and inhibits TGF-ß signaling. Targeting CEA with either CEA-specific antibody or siRNA rescues TGF-ß response in colorectal cancer cell lines with elevated CEA, thereby restoring the inhibitory effects of TGF-ß signaling on proliferation. CEA also enhances the survival of colorectal cancer cells in both local colonization and liver metastasis in animal study. Our study provides novel insights into the interaction between CEA and TGF-ß signaling pathway and establishes a negative feedback loop in amplifying the progression of colon cancer cells to more invasive phenotypes. These findings offer new therapeutic opportunities to inhibit colorectal cancer cell proliferation by cotargeting CEA in promoting tumor-inhibitory action of the TGF-ß pathway.

Efficacy of metformin therapy in adolescent girls with androgen excess: relation to sex hormone-binding globulin and androgen receptor polymorphisms.

We studied the effects of the SHBG (TAAAA)(n) and androgen receptor gene [AR] (CAG)(n) allele length on endocrine-metabolic features and body composition (by dual-energy X-ray absorptiometry) before and after 1 year on metformin (850 mg/d) in 70 girls with polycystic ovary syndrome after precocious pubarche; allele lengths were assessed by polymerase chain reaction in both patients and in population control subjects (n = 107). Longer SHBG (TAAAA)(n) alleles (>8 repeats) were associated with more improvement of the lipid profile after 1 year on metformin, whereas longer AR (CAG)(n) alleles were related to more normalization of the androgen and lipid levels after therapy; longer alleles in both genes had an additive effect on the beneficial changes of SHBG, T, and lipids after metformin.

Microsatellite instability at tetranucleotide repeats in sporadic colorectal cancer in Japan.

Most tumors of patients with Lynch syndrome and a fraction of sporadic colorectal cancers (CRCs) exhibit high levels of microsatellite instability (MSI) at mono- and dinucleotide repeat loci. A different type of instability, elevated microsatellite alterations at selected tetranucleotide repeats (EMAST) has been found in non-colonic cancers. Our previous study demonstrated that EMAST is common in sporadic CRC. Here, we focused on the relationships between EMAST and other genomic instability parameters or clinicopathological features in an unselected series of 88 sporadic CRCs. Of the tumors in the sample, 4 (4.5%) were MSI-high (MSI-H), 9 (10.2%) were MSI-low (MSI-L) and 75 (85.2%) were microsatellite stable. EMAST status was determined using 7 EMAST markers. Fifty-three (60.2%) tumors without MSI-H showed instability at >or=1 EMAST loci. All 4 MSI-H tumors showed instability at several EMAST loci. Instability profiles of MSI-H tumors at EMAST loci were more complex than those of non-MSI-H tumors. A tendency of positive association was observed between MSI-L and EMAST (P=0.023). The frequency of loss of heterozygosity (LOH) for the 14 loci in EMAST-positive tumors was significantly higher than negative tumors (P=0.048). Among the clinicopathological parameters, only tumor location at the distal colon was associated with EMAST-negative tumors (P=0.0084, one-tailed). A relatively higher frequency of well-differentiated adenocarcinomas was observed in EMAST tumors as opposed to non-EMAST tumors, though the survival rate was similar. These results suggest that overlapping mechanisms that cause MSI-L, EMAST and LOH in CRCs may exist.

Concentration and microsatellite status of plasma DNA for monitoring patients with renal carcinoma.

We verified the feasibility of plasma bound method for detecting renal cell carcinoma (RCC) combining the study of plasma DNA concentration and microsatellite alterations (LOH). Plasma DNA concentration was evaluated with real-time PCR in 54 patients with renal neoplasm before surgery and in 20 of these patients during a 26-64 month follow-up. Microsatellite study was performed on tumour tissue DNA of 33 RCC clear cell (RCCcc) and on plasma DNA of 14 RCCcc patients during preoperative and/or follow-up period. Patients had a significantly high (26.4+/-48.3 ng/ml versus controls 3.2+/-1.5 ng/ml; p=0.003) preoperative plasma DNA concentration that decreased after nephrectomy. During follow-up, plasma DNA increased in 12 patients without evidence of neoplasia; 3 patients successively relapsed. Tumour tissue DNA of 25 RCCcc patients (75.8%) displayed microsatellite LOH. Preoperative plasma DNA of 9 patients harboured LOH in 5 cases (55.6%). Augmented plasma DNA of 7 patients displayed LOH in 3 cases (42.9%) at follow-up, and in 1 case preceded the recurrence of disease. Plasma DNA concentration combined with microsatellite LOH in plasma DNA may predict disease recurrence in RCC patients.

Microsatellite in the 3' untranslated region of human fibroblast growth factor 9 (FGF9) gene exhibits pleiotropic effect on modulating FGF9 protein expression.

Fibroblast growth factor 9 (FGF9) is a member of secreted polypeptide families and involved in many important biological processes, including implantation and morphogenesis during embryogenesis and adult life. Recently, Fgf9-knockout mice exhibited male-to-female sex reversal, demonstrating a novel function for FGF9 in testicular development. We hypothesized that FGF9 is involved in sex development at an early embryonic stage in humans. In this study, we systematically screened sequences of the FGF9 gene in 21 XY females and 72 XX females and XY males to examine whether sequence variants of the FGF9 gene play a pathophysiological role on human gonadal dysgenesis. No mutation was identified, but a single nucleotide variant and two microsatellites were found. The allelic distribution of polymorphic microsatellite in the 3'-UTR of FGF9 between patients and controls was slightly different with Bonferroni correction (P=0.06). We further applied reporter gene system and quantitative RT-PCR to study the function of this microsatellite motif and results demonstrated that the (TG)(n) motif modulated gene expression at both pre- and post-transcriptional levels. The (TG)(14) allele, which showed a potential association with male-to-female sex reversal (odds ratio=6.08, 95% confidence interval=1.39-26.63), displayed the strongest promoter activity and longest mRNA stability. These data demonstrated that 3'-UTR microsatellite of the FGF9 is a functional polymorphism that plays dual roles in regulating FGF9 expression. Although our preliminary result suggested a possible association between FGF9 and human gonadal dysgenesis, the major limitation of small dataset in this study points out the requirement for further investigation.

Influence of polymorphisms at loci encoding DNA repair proteins on cancer susceptibility and G2 chromosomal radiosensitivity.

Sixteen candidate polymorphisms (13 SNPs and 3 microsatellites) in nine genes from four DNA repair pathways were examined in 83 subjects, comprising 23 survivors of childhood cancer, their 23 partners, and 37 offspring, all of whom had previously been studied for G(2) chromosomal radiosensitivity. Genotype at the Asp148Glu SNP site in the APEX gene of the base excision repair (BER) pathway was associated with childhood cancer in survivors (P = 0.001, significant even after multiple test adjustment), due to the enhanced frequency of the APEX Asp148 allele among survivors in comparison to that of their partners. Analysis of variance (ANOVA) of G(2) radiosensitivity in the pooled sample, as well as family-based association test (FBAT) of the family-wise data, showed sporadic suggestions of associations between G(2) radiosensitivity and polymorphisms at two sites (the Thr241Met SNP site in the XRCC3 gene of the homologous recombinational pathway by ANOVA, and the Ser326Cys site in the hOGG1 gene of the BER pathway by FBAT analysis), but neither of these remained significant after multiple-test adjustment. This pilot study provides an intriguing indication that DNA repair gene polymorphisms may underlie cancer susceptibility and variation in radiosensitivity.

SnoN expression is differently regulated in microsatellite unstable compared with microsatellite stable colorectal cancers.

BACKGROUND: SnoN is an important regulator of the transforming growth factor beta (TGFbeta) signalling pathway and has been shown to exhibit both tumour promotion and suppression activity. METHODS: To further explore the role of this complex molecule in colorectal tumorigenesis, we examined 52 paired normal and tumour colorectal specimens stratified by level of microsatellite instability; 18 with high-level microsatellite instability (MSI-H) and 34 microsatellite stable (MSS). SnoN transcript expression was quantitated by real-time PCR and analysed with respect to clinical indicators of prognosis. RESULTS: Within the MSI-H subgroup, SnoN was commonly either up-regulated (6/18, 33%) or down-regulated (7/18, 39%). A significantly different distribution of SnoN expression was observed in MSS cancers compared with MSI-H (P < or = 0.001). Whilst 17/34 (50%) of MSS tumours demonstrated up-regulation, none showed down-regulated expression. Within the MSI-H subgroup, up-regulation was significantly correlated with lack of repeat tract mutation in the TGFbetaRII gene (P < or = 0.025), suggesting that SnoN is more frequently up-regulated in the presence of functional TGFbeta signalling. CONCLUSION: Together these data support the notion that SnoN has both oncogenic and tumour suppressive properties depending on other genetic changes within the tumour, and that the MSI-H pathway of colorectal tumorigenesis presents an excellent model for the study of these opposing functions.

SHBG gene promoter polymorphisms in men are associated with serum sex hormone-binding globulin, androgen and androgen metabolite levels, and hip bone mineral density.

CONTEXT: SHBG regulates free sex steroid levels, which in turn regulate skeletal homeostasis. Twin studies have demonstrated that genetic factors largely account for interindividual variation in SHBG levels. Glucuronidated androgen metabolites have been proposed as markers of androgenic activity. OBJECTIVE: Our objective was to investigate whether polymorphisms in the SHBG gene promoter [(TAAAA)(n) microsatellite and rs1799941 single-nucleotide polymorphism] are associated with serum levels of SHBG, sex steroids, or bone mineral density (BMD) in men. DESIGN AND STUDY SUBJECTS: We conducted a population-based study of two cohorts of Swedish men: elderly men (MrOS Sweden; n congruent with 3000; average age, 75.4 yr) and young adult men (GOOD study; n = 1068; average age, 18.9 yr). MAIN OUTCOME MEASURES: We measured serum levels of SHBG, testosterone, estradiol, dihydrotestosterone, 5alpha-androstane-3alpha,17beta-diol glucuronides, androsterone glucuronide, and BMD determined by dual-energy x-ray absorptiometry. RESULTS: In both cohorts, (TAAAA)(n) and rs1799941 genotypes were associated with serum levels of SHBG (P < 0.001), dihydrotestosterone (P < 0.05), and 5alpha-androstane-3alpha,17beta-diol glucuronides (P < 0.05). In the elderly men, they were also associated with testosterone and BMD at all hip bone sites. The genotype associated with high levels of SHBG was also associated with high BMD. Interestingly, male mice overexpressing human SHBG had increased cortical bone mineral content in the femur, suggesting that elevated SHBG levels may cause increased bone mass. CONCLUSIONS: Our findings demonstrate that polymorphisms in the SHBG promoter predict serum levels of SHBG, androgens, and glucuronidated androgen metabolites, and hip BMD in men.

Tetranucleotide repeats in coding regions: no evidence for involvement in EMAST carcinogenesis.

Genetic instability is a hallmark of malignancy. In the majority of malignant tumors, chromosomal instability leads to major numerical and structural chromosomal aberrations. In contrast, some tumors have a deficient DNA mismatch repair system and accumulate mutations particularly in repetitive mono- and dinucleotide sequences, a phenomenon referred to as microsatellite instability (MSI). Recently, a novel phenotype of tumors presenting with elevated microsatellite alterations at selected tetranucleotide repeats (EMAST) has been reported. To date, not much is known about the molecular mechanisms of EMAST tumorigenesis. In MSI tumors, instability at specific mono- and dinucleotide repeats leads to alteration of genes carrying these repeats and thus may contribute to MSI tumorigenesis. We hypothesized that, similarly to the MSI phenotype, development of EMAST cancers may be promoted by mutations affecting tetranucleotides located in coding regions of the genome. To test this hypothesis, we performed a genome-wide database search to identify tetranucleotides in gene-encoding regions. Only seven tetranucleotide repeats located in predicted gene-encoding regions were retrieved. Allele length analysis yielded three remaining candidates with a monomorphic pattern in healthy individuals. Mutation analysis revealed that none of these three candidates displayed mutations in EMAST-positive bladder cancers. These data suggest that mutational inactivation of tetranucleotide-containing genes is very unlikely to contribute to the progression of EMAST tumors.

Mutually exclusive promoter hypermethylation patterns of hMLH1 and O6-methylguanine DNA methyltransferase in colorectal cancer.

Hypermethylation of CpG islands in gene promoter regions is an important mechanism of gene inactivation in cancer. Many cellular pathways, including DNA repair, are inactivated by this type of epigenetic lesion, resulting in proposed mutator phenotypes. Promoter hypermethylation of hMLH1 has been implicated in a subset of colorectal cancers that show microsatellite instability (MSI). Transcriptional silencing of O6-methylguanine DNA methyltransferase (MGMT) has also been described in a variety of neoplasms and has been associated with a consequent mutational spectrum. We investigated the relationship between hMLH1 promoter hypermethylation and MGMT promoter hypermethylation in 110 colorectal cancers using methylation-specific polymerase chain reaction. Expression of hMLH1 and MGMT was assessed by immunohistochemistry. MSI testing was performed using the National Cancer Institute consensus panel of five microsatellite markers. Promoter hypermethylation of hMLH1 was detected in 12% of tumors. This was significantly associated with the MSI-high phenotype (P < 0.01) and loss of hMLH1 expression (P < 0.01). Methylation of the MGMT promoter was detected in 43% of tumors, which were mostly microsatellite stable or MSI-low (P = 0.041) and showed loss of MGMT expression (P < 0.01). We demonstrated an inverse relationship between hMLH1 promoter hypermethylation and MGMT promoter hypermethylation (P = 0.041), suggesting that a number of distinct hypermethylation-associated pathways may exist in colorectal cancer.

Microsatellite instability in sporadic and inherited colon adenocarcinomas from Greek patients: correlation with several clinicopathological characteristics.

BACKGROUND AND AIMS: Microsatellite instability seems to play a significant role in colorectal carcinogenesis, as it is reported to occur in HNPCC patients as well as in a proportion of sporadic cases. The aim of this study was to examine the presence of microsatellite instability in relation to other commonly observed genetic abnormalities and clinicopathological characteristics of sporadic and inherited colorectal cancers. METHODOLOGY: One hundred and three sporadic colorectal adenocarcinomas and 9 adenocarcinomas from HNPCC patients were histologically evaluated. The presence of microsatellite instability was investigated at six loci. K-ras and p53 mutations, p53 LOH, hMLH1 expression and methylation status were examined as well. Statistical analysis was performed to define possible correlations of the observed genetic alterations with the clinicopathological characteristics of the analysed tumors. RESULTS: High-grade microsatellite instability was found in 14% of sporadic adenocarcinomas and in 78% of adenocarcinomas from HNPCC patients. K-ras and p53 mutations were found in 29% and 28% of sporadic adenocarcinomas respectively and in 0% and 22% of the 9 HNPCC cases. A statistically significant correlation was noticed in sporadic tumors between the presence of MSI-H and tumor location at the proximal colon, as well as with the female gender. CONCLUSIONS: Sporadic MSI+ colon adenocarcinomas seem to represent a distinct entity with a unique profile of genetic changes, different from those observed in HNPCC or MSI negative sporadic tumors.