Tumor IHC analysis of four MMR proteins and MSI testing provide a highly sensitive strategy for identifying MMR gene mutation-carrying, early-onset colorectal cancer patients, half of whom would have been missed using Amsterdam Criteria alone. Tumor-based approaches for triaging early-onset colorectal cancer patients for MMR gene mutation testing, irrespective of family history, appear to be an efficient screening strategy for HNPCC.

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The aim of our study was to examine the role of genetic factors on early-onset colorectal cancer after excluding the impact of germline mutations in the two major mismatch repair genes. A total of 131 incident probands, under 45 years at diagnosis of a first primary colorectal cancer selected from the Victorian Cancer Registry, and their first-and seconddegree relatives, were interviewed. Germline DNA from all 12 probands with a family history meeting the modified Amsterdam Criteria for Hereditary Non-Polyposis Colorectal Cancer (HNPCC) and a random sample of 31 of the remaining probands was screened for mutations in hMSH2 and hMLH1 via manual sequencing. Germline mutations were identified in 6 of the 131 probands (5%), all from the "HNPCC" families. Of the remaining 125 probands, 51 (41%) reported at least one first-or second-degree relative with colorectal cancer with an excess of colorectal cancer in firstdegree relatives (SMR ‫؍‬ 2.7, 95% CI ‫؍‬ 1.7-4.1, p < 0.001). The lifetime risk to age 70 for first-degree relatives was 8.0% (5.0 -12.8%), compared to the Victorian population risk of 3.2% (p ‫؍‬ 0.01). The best fitting major gene model was a recessively-inherited risk of 98% to age 70 (95% CI ‫؍‬ 24 -100%) carried by 0.17% of the population and would explain 15% of all colorectal cancer in cases with a diagnosis before age 45. Early-onset colorectal cancer is strongly familial even after excluding families found to be segregating a mutation in either of the 2 major mismatch repair genes. There is evidence for a role of yet to be identified genes associated with a high recessively-inherited risk of colorectal cancer. © 2002 Wiley-Liss, Inc. Germline mutations in several mismatch repair genes have been identified that greatly increase the risk of colorectal cancer and, to a lesser extent, cancer of other sites including the endometrium and small bowel. 1 Mutations in 2 of the mismatch repair genes, hMSH2 and hMLH1, have been found to be segregating with disease in about 50% of multiple-case, multi-generational families meeting the Amsterdam Criteria for hereditary non-polyposis colorectal cancer (HNPCC). 2,3 These families have at least 3 relatives diagnosed with colorectal cancer, at least 1 affected member being a first-degree relative of at least 2 other affected relatives, at least 2 affected relatives in successive generations and at least 1 affected member diagnosed before age 50. 1 Few instances of germline mutations in hMSH2 or hMLH1 have been documented outside HNPCC families except in those diagnosed with colorectal cancer at a very young age 4 -6 and only a small proportion of HNPCC families appear to have segregating a mutation in other mismatch repair genes, such as hMSH6. 7 Family history is one of the strongest predictors of colorectal cancer. 8 -12 A recent meta-analysis found that having a first-degree relative with colorectal cancer approximately doubled the risk of colorectal cancer and if the affected relative was diagnosed before age 45 the risk was approximately 4-fold. 13 What is ...

Purpose: Microsatellite instability (MSI) testing of colorectal cancer tumors is used as a screening tool to identify patients most likely to be mismatch repair (MMR) gene mutation carriers. We wanted to examine which microsatellite markers currently used to detect MSI best predict earlyonset colorectal cancer caused by germ-line mutations in MMR genes. Experimental Design: Invasive primary tumors from a population-based sample of 107 cases of colorectal cancer diagnosed before age 45 years and tested for germ-line mutations in MLH1, MSH2, MSH6, and PMS2 and MMR protein expression were screened for MSI using the National Cancer Institute panel and an expanded 10-microsatellite marker panel. MSI-High cancers and all MLH1 and MSH2 mutation carriers (100% sensitive). Bat40 and Bat25 were unstable in all tumors of MSH6 mutation carriers (100% sensitive). Bat40 was unstable in all MMR gene mutation carriers (100% sensitive). By incorporating seven mononucleotide repeats markers into the 10-marker panel, we were able to distinguish the carriers of MSH6 mutations (all scored 10 MSI-Low) from the MLH1 and MSH2 mutation carriers (all scored 10 MSI-High). Conclusions: In early-onset colorectal cancer, a microsatellite panel containing a high proportion of mononuclear repeats can distinguish between tumors caused by MLH1 and MSH2 mutations from those caused by MSH6 mutations.

Objective Chromosomal loss within the region of 18q and loss of SMAD4 expression have been reported to be frequent somatic events during colorectal cancer tumour progression; however, their associations with age at onset have not been widely studied. Method We analysed 109 tumours from a population-based case-family study based on colorectal cancers diagnosed before the age of 45 years. These patients with early-onset colorectal cancer had been previously screened for germ-line mismatch repair gene mutations, microsatellite instability (that included the mononucleotide repeat in TGFβRII) and somatic k-ras mutations. We measured SMAD4 protein expression using immunohistochemistry and SMAD4 copy number using quantitative real-time PCR. Results Loss of SMAD4 protein expression was observed in 27/109 (25%) of cancers tested and was more commonly observed in rectal tumours (15/41, 36%) when compared with tumours arising in the colon (11/66, 17%) (P = 0.04). There was no association between SMAD4 protein expression and TGFβR11 mutation status, SMAD4 copy number, family history, MSI status, tumour stage or grade. Conclusion Loss of SMAD4 expression is a common feature of early-onset colorectal tumours as it is in colorectal cancers diagnosed in other age-groups. Taken together, the molecular pathways (genetic and epigenetic) now known to be involved in early-onset colorectal cancer only explain a small proportion of the disease and require further exploration.

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The Muir-Torre syndrome (MTS) is an autosomal dominantly inherited disorder, characterized by visceral malignancies and sebaceous skin lesions. In a subset of MTS families the disease is due to an underlying DNA mismatch-repair defect. We have identified a MTS family whose spectrum of reported neoplasia included adenocarcinomas of numerous gastrointestinal sites, carcinomas of the endometrium, ovary and breast, papillary transitional cell carcinoma of the ureter, a range of cutaneous tumors, as well as keratoacanthomas. All tumors were tested for microsatellite instability and immunohistochemically stained for expression of MLH1 and MSH2 proteins. All tumors were found to be microsatellite unstable and lacking in MSH2 protein expression. The subsequent mutation detection focused on hMSH2, and a germline mutation was identified (CAA-->TAA, Gln-->STOP, codon 337). This mutation was subsequently found in a family member with a single skin lesion only. We propose that the combination of immunohistologic and microsatellite instability analysis can be exploited to screen individuals with characteristic skin lesions even before development of visceral tumors and to direct the subsequent germline mutation search. The profile of microsatellite instability and the genes rendered dysfunctional differed between tumor samples, suggesting that the molecular pathogenesis varied between lesions, despite a common germline mutation.

Genetic diseases associated with dynamic mutations in microsatellite DNA often display parent-of-origin effects (POEs) in which the risk of disease depends on the sex of the parent from whom the disease allele was inherited. Carriers of germline mutations in mismatch repair (MMR) genes have high risks of colorectal carcinoma (CRC). We investigated whether these risks depend on the parent-of-origin of the mutation. We studied 422 subjects, including 89 MMR gene mutation carriers, from 17 population-based families who were each recruited via a CRC case diagnosed before age 45 years and found to carry a MMR gene mutation. The POE hazard ratio (HRPOE), defined to be the CRC incidence for carriers with maternally derived mutations divided by the corresponding paternal incidence, was estimated using a novel application of modified segregation analysis. HRPOE (95% confidence interval) was estimated to be 3.2 (1.1–9.8) for males (P=0.03) and 0.8 (0.2–2.8) for females (P=0.5) and the corresponding cumulative risks to age 80 years were 88% (54%–100%) for male carriers with maternally derived mutations and 38–48% for all other carriers. If confirmed by larger studies, these results will have important implications for the etiology of CRC and for the clinical management of MMR gene mutation carriers.