High-level microsatellite instability (MSI-H) is demonstrated in 10 to 15% of sporadic colorectal cancers and in most cancers presenting in the inherited condition hereditary nonpolyposis colorectal cancer (HNPCC). Distinction between these categories of MSI-H cancer is of clinical importance and the aim of this study was to assess clinical, pathological, and molecular features that might be discriminatory. One hundred and twelve MSI-H colorectal cancers from families fulfilling the Bethesda criteria were compared with 57 sporadic MSI-H colorectal cancers. HNPCC cancers presented at a lower age (P < 0.001) with no sporadic MSI-H cancer being diagnosed before the age of 57 years. MSI was less extensive in HNPCC cancers with 72% microsatellite markers showing band shifts compared with 87% in sporadic tumors (P < 0.001). Absent immunostaining for hMSH2 was only found in HNPCC tumors. Methylation of hMLH1 was observed in 87% of sporadic cancers but also in 55% of HNPCC tumors that showed loss of expression of hMLH1 (P = 0.02). HNPCC cancers were more frequently characterized by aberrant beta-catenin immunostaining as evidenced by nuclear positivity (P < 0.001). Aberrant p53 immunostaining was infrequent in both groups. There were no differences with respect to 5q loss of heterozygosity or codon 12 K-ras mutation, which were infrequent in both groups. Sporadic MSI-H cancers were more frequently heterogeneous (P < 0.001), poorly differentiated (P = 0.02), mucinous (P = 0.02), and proximally located (P = 0.04) than HNPCC tumors. In sporadic MSI-H cancers, contiguous adenomas were likely to be serrated whereas traditional adenomas were dominant in HNPCC. Lymphocytic infiltration was more pronounced in HNPCC but the results did not reach statistical significance. Overall, HNPCC cancers were more like common colorectal cancer in terms of morphology and expression of beta-catenin whereas sporadic MSI-H cancers displayed features consistent with a different morphogenesis. No individual feature was discriminatory for all HNPCC cancers. However, a model based on four features was able to classify 94.5% of tumors as sporadic or HNPCC. The finding of multiple differences between sporadic and familial MSI-H colorectal cancer with respect to both genotype and phenotype is consistent with tumorigenesis through parallel evolutionary pathways and emphasizes the importance of studying the two groups separately.

No abstract

Background-10% of sporadic colorectal cancers are characterised by a low level of microsatellite instability (MSI-L). These are not thought to diVer substantially from microsatellite-stable (MSS) cancers, but MSI-L and MSS cancers are distinguished clinicopathologically and in their spectrum of genetic alterations from cancers showing high level microsatellite instability (MSI-H). Aims-To study the distribution of molecular alterations in a series of colorectal cancers stratified by DNA microsatellite instability. Methods-A subset of an unselected series of colorectal cancers was grouped by the finding of DNA MSI at 0 loci (MSS) (n = 51), 1-2 loci (MSI-L) (n = 38) and 3-6 loci (MSI-H) (n = 25). The frequency of K-ras mutation, loss of heterozygosity (LOH) at 5q, 17p and 18q, and patterns of p53 and catenin immunohistochemistry was determined in the three groups. Results-MSI-H cancers had a low frequency of K-ras mutation (7%), LOH on chromosomes 5q (0%), 17p (0%) and 18q (12.5%), and a normal pattern of immunostaining for p53 and catenin. MSI-L cancers diVered from MSS cancers in terms of a higher frequency of K-ras mutation (54% v 27%) (p = 0.01) and lower frequency of 5q LOH (23% v 48%) (p = 0.047). Whereas aberrant catenin expression and 5q LOH were concordant (both present or both absent) in 57% of MSS cancers, concordance was observed in only 20% of MSI-L cancers (p = 0.01). Conclusions-MSI-L colorectal cancers are distinct from both MSI-H and MSS cancers. This subset combines features of the suppressor and mutator pathways, may be more dependent on K-ras than on the APC gene in the early stages of neoplastic evolution, and a proportion may be related histogenetically to the serrated (hyperplastic) polyp. (J Clin Pathol 1999;52:455-460)

+ and M30 + random apoptosis counts (p<0.001). However, TILs and apoptosis showed little colocalisation. Conclusions-While TILs might be expected to explain the increased apoptotic rate and improved prognosis of MSI-H cancers, it is likely that TILs and apoptosis are independent characteristics of MSI-H cancers. (Gut 2001;48:360-366)

No abstract

Adenomas are the precursors of most colorectal cancers. Hyperplastic polyps have been linked to the subset of colorectal cancers showing DNA microsatellite instability, but little is known of their underlying genetic etiology. Using a strategy that isolates differentially methylated sequences from hyperplastic polyps and normal mucosa, we identified a 370-bp sequence containing the 5 untranslated region and the first exon of a gene that we have called HPP1. Rapid amplification of cDNA ends was used to isolate HPP1 from normal mucosa. Using reverse transcription-PCR, HPP1 was expressed in 28 of 30 (93%) normal colonic samples but in only seven of 30 (23%) colorectal cancers (P < 0.001). The 5 region of HPP1 included a CpG island containing 49 CpG sites, of which 96% were found to be methylated by bisulfite sequencing of DNA from colonic tumor samples. By COBRA analysis, methylation was detected in six of nine (66%) adenomas, 17 of 27 (63%) hyperplastic polyps, and 46 of 55 (84%) colorectal cancers. There was an inverse relationship between methylation level and mRNA expression in cancers (r ‫؍‬ ؊0.67; P < 0.001), and 5-aza-2-deoxycytidine treatment restored HPP1 expression in two colorectal cancer cell lines. In situ hybridization of HPP1 indicated that expression occurs in epithelial and stromal elements in normal mucosa but is silenced in both cell types in early colonic neoplasia. HPP1 is predicted to encode a transmembrane protein containing follistatin and epidermal growth factor-like domains. Silencing of HPP1 by methylation may increase the probability of neoplastic transformation.

comprises multiple cumulative genetic alterations, consistent The tumor suppressor gene CDKN2A (MTS1/p16), lowith the multistage nature of all late onset cancers, 5 which cated on chromosome 9p21, is inactivated in a variety of has been well investigated in colorectal cancer. tumors including melanomas and tumors of the biliaryThe multiple genetic alterations that occur in human cantract, pancreas, and stomach. The aim of the present cer target both oncogenes and tumor suppressor genes. 7 Tustudy was to determine whether this gene is inactivated mor suppressor genes function as negative regulators of cell in hepatocellular carcinoma (HCC). Twenty-three priproliferation, the loss of function being associated with the mary HCCs and four HCC cell lines were examined. Loss emergence of a cancerous phenotype. 8 Frequent loss of hetof heterozygosity (LOH) analysis was performed using erozygosity (LOH) at specific chromosomal loci in tumor eight polymorphic markers immediately surrounding DNA, detected by polymorphic DNA markers, can identify CDKN2A, and showed a contiguous region of loss, with specific chromosomal regions associated with malignancy the two most commonly deleted markers being D9S1604, and suggest the presence of a tumor suppressor gene in that located between the p16 and p15 genes, at which 7 of 13 region that may have been inactivated by such loss. For exinformative tumors (54%) showed loss, and D9S171, with ample, the p53 gene has been shown to be inactivated by 4 of 14 LOH (29%). Exons 1, 2, and 3 of CDKN2A were LOH in 30% to 70% of HCCs from patients living in countries amplified by polymerase chain reaction to detect homoin which HCC is prevalent.9 zygous deletions, and single-strand conformation polyThe tumor suppressor gene CDKN2A (MTS1/p16) located morphism (SSCP) analysis was performed to screen for on chromosome 9p21-22 appears to be frequently involved in mutations. No homozygous deletions were detected in many types of cancer, including melanoma, 10 biliary tract any sample. SSCP and sequence analysis showed the cancers, 11 pancreatic cancers, 12 and gastric carcinomas. 13 The same nucleotide change at codon 148 in four tumors.changes involve translocation, inversion, LOH, and homozyThis has been reported elsewhere as a polymorphism.gous deletion. The gene CDKN2A comprises three exons that One of these four tumors also contained a mutation at encode the protein p16, an inhibitor of a cyclin-dependent codon 119, resulting in the substitution of an acidic kinase (cdk-4) which negatively regulates the cell cycle. 14 Alamino acid for a basic one. It is concluded that CDKN2A though alteration of CDKN2A exon 2 has been investigated is infrequently deleted or mutated in HCC. The region previously in HCC, 15 chromosome 9p LOH including of allelic loss upstream from CDKN2A might result in CDKN2A has not been studied extensively in HCC. To examinactivation of regulatory sequences important in the ine whether suppressor loci on chromosome 9p are involved expression of this gene; alternatively, a seco...

No abstract