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Aim: Medullary carcinoma is a recently described subtype of mismatch repair deficient (MMRd) colorectal carcinoma (CRC) which, despite being poorly differentiated by traditional morphological criteria, has been reported to have a good prognosis. We investigated the pathological and clinical features of medullary CRC in an unselected cohort of CRCs undergoing surgical resection., Methods: All CRCs resected within a single health district database from 1998 to 2012 were categorized prospectively and underwent retrospective review to identify 91 medullary CRCs, with 11 additional cases from 2013 to 2014. Strict criteria were employed to diagnose medullary carcinoma requiring both MMRd and greater than 90 % of the tumor to demonstrate typical morphology, including solid growth. The demographic and pathological features, as well as all-cause survival, were compared with other CRCs, and specifically to other MMRd CRCs., Results: From 1998 to 2012, 91 of 3,295 CRCs (2.8 %) were of the medullary type. Medullary CRC was more likely to arise in females than males (3.3:1; p < 0.0001), the elderly (mean age 77 vs. 71 years; p < 0.001), and the right colon (86 %; p < 0.0001). All medullary CRCs demonstrated MMR deficiency (considered an inclusion criteria) and 86 % were BRAFV600E-mutated (p < 0.0001). Thirty-day mortality after resection was higher in medullary CRC (4.6 vs. 1.7 %; p = 0.049). On univariate analysis, survival was not better than well-differentiated or other MMRd tumors. However, using a multivariate model, a medullary phenotype was protective (hazard ratio of death 0.54, 95 % CI 0.30-0.96; p = 0.037)., Conclusions: Medullary CRC is more common than previously reported, frequently presents with locally advanced disease, and may be associated with higher mortality at 30 days after resection. Despite this, when strict criteria are used for diagnosis, the overall survival is favorable when compared with CRCs with equivalent demographic and pathological characteristics.

Mutation specific immunohistochemistry (IHC) is a promising new technique to detect the presence of the BRAFV600E mutation in colorectal carcinoma (CRC). When performed in conjunction with mismatch repair (MMR) IHC, BRAFV600E IHC can help to further triage genetic testing for Lynch Syndrome. In a cohort of 1426 patients undergoing surgery from 2004 to 2009 we recently demonstrated that the combination of MMR and BRAFV600E IHC holds promise as a prognostic marker in CRC, particularly because of its ability to identify the poor prognosis MMR proficient (MMRp) BRAFV600E mutant subgroup. We attempted to validate combined MMR and BRAFV600E IHC as a prognostic indicator in a separate cohort comprising consecutive CRC patients undergoing surgery from 1998 to 2003. IHC was performed on a tissue microarray containing tissue from 1109 patients with CRC. The 5 year survivals stratified by staining patterns were: MMRd/BRAFwt 64%, MMRd/BRAFV600E 64%, MMRp/BRAFwt 60% and MMRp/BRAFV600E 53%. Using the poor prognosis MMRp/BRAFV600E phenotype as baseline, univariate Cox regression modelling demonstrated the following hazard ratios for death: MMRd/BRAFwt HR = 0.71 (95%CI = 0.40-1.27), p = 0.31; MMRd/BRAFV600E HR = 0.74 (95%CI = 0.51-1.07), p = 0.11 and MMRp/BRAFwt HR = 0.79 (95%CI = 0.60-1.04), p = 0.09. Although the findings did not reach statistical significance, this study supports the potential role of combined MMR and BRAF IHC as prognostic markers in CRC.

Background: TGFbeta is an important cell growth regulator which may have a role in metastasis formation. Microsatellite unstable (MSI-H) colon cancer serves as a unique model to demonstrate this as most MSI-H colon cancers have a mutation in the transforming growth factor beta receptor II (TGFbetaRII) gene and a low metastatic rate., Aims: To demonstrate an increase in invasion and metastasis in a MSI-H colorectal cancer cell line with a known mutation in TGFbetaRII., Materials and Methods: By restoring the wild-type TGFbetaRII gene in the KM12C MSI-H colorectal carcinoma cell line with a known mutation in TGFbetaRII, we have demonstrated that both invasion and metastasis in this cell line was significantly increased. A mouse metastatic model have shown that liver metastases were increased in mice inoculated with cells containing a wild-type TGFbetaRII gene (42% for the transfected group compared with 15% for the control group; p = 0.0379), despite a reduction in the size of primary tumours., Conclusions: This study highlights an important mechanism which may contribute to the low metastatic rate of MSI-H colon cancers and demonstrates the importance of TGFbeta signalling in metastasis formation. Previous studies involving breast cancer cell lines have shown that blocking TGFbeta signalling results in a reduction in metastasis formation. This study is the first study to use a cell line with a low metastatic rate and TGFbetaRII mutations to demonstrate that restoring TGFbeta signalling increases the metastatic rate.

Immunohistochemistry of tumour samples is increasingly used in the triage of families where hereditary non-polyposis colorectal cancer (HNPCC) due to mismatch repair defects is suspected. Usually, this is undertaken in tumours that are a recognised part of the spectrum of HNPCC-related cancers e.g. colon or endometrial cancers. Although breast cancers are not classed as part of this spectrum, this study examined the extent to which some breast tumours do arise by the mismatch repair pathway in these families. This may have clinical utility in families where an individual with a 'classic HNPPC-related' tumour is not available for evaluation. Immunohistochemistry of a breast tumour may identify an individual in whom germline mutation testing is worthwhile.

Introduction: High-frequency microsatellite instability (MSI-H) is an alternate pathway of colorectal carcinogenesis, which accounts for 15% of all sporadic colorectal cancers. These tumours arise from mutations in the DNA mismatch repair system and thus have different responses to chemotherapeutic agents compared to microsatellite stable (MSS) cancers., Objective: This review aims to summarise the available literature on the responses to chemotherapy in MSI-H colorectal cancer (CRC)., Results and Discussion: 5 Fluorouracil (5FU) is commonly used as a chemotherapeutic agent in colon cancer and in vitro evidence shows reduced response to 5FU in MSI-H CRC. The clinical evidence is conflicting but favours a reduced response to 5FU in MSI-H CRC. Several newer agents such as COX-2 inhibitors and irinotecan are also reviewed., Conclusion: Available evidence suggests that MSI-H CRC have different behaviour patterns and response to chemotherapy compared with MSS CRC.

Microsatellite instability is a recognised pathway of colorectal carcinogenesis responsible for about 15% of all sporadic colorectal cancers. Recent evidence has suggested that these tumours may not have the same response as microsatellite stable colon cancers to 5-fluorouracil (5FU)-based chemotherapy. The response to 5FU in four microsatellite unstable (MSI-H) cell lines was examined by cell viability assays and invasion assays. Flow cytometry was used to assess the effect of 5FU on MSI-H cell lines. In vivo response to 5FU was assessed by intraperitoneal injection of 5FU or control to 80 nude mice that had received intrasplenic injections of an MSI-H cell line KM12C prior to commencing treatment. There was inhibition of cell growth in MSI-H cell lines when treated with 5FU. There was no difference in invasiveness in the MSI-H cell lines when treated with 5FU. Primary tumours formed in 27 of the untreated and 25 of the 5FU treated mice (p=NS). There was a 36% reduction in splenic weight in those mice treated with 5FU (p<0.03). Metastases formed in 5 of the untreated and 9 of the treated mice (p=0.12). 5FU treatment of MSI-H tumours results in a reduction in growth but does not result in a reduction in invasion or metastasis.

Irinotecan (CPT-11) is a prodrug that is used to treat metastatic colorectal cancer. It is activated to the topoisomerase poison SN-38 by carboxylesterases. SN-38 is subsequently metabolised to its inactive glucuronide, SN-38G, which can however be reactivated to SN-38 by beta-glucuronidase. The purpose of this study was to examine the role of carboxylesterases and beta-glucuronidase in the in vitro production of SN-38 in human colorectal tumours. The production of SN-38 from CPT-11 and SN-38G was measured by HPLC in human colorectal tumour homogenates. Carboxylesterase and beta-glucuronidase activities were found to be lower in tumour tissues compared to matched normal colon mucosa samples. In colorectal tumour, beta-glucuronidase and carboxylesterase-mediated SN-38 production rates were comparable at clinically relevant concentrations of SN-38G and CPT-11, respectively. Therefore, tumour beta-glucuronidase may play a significant role in the exposure of tumours to SN-38 in vivo, particularly during prolonged infusions of CPT-11.

This study investigates the molecular features of metastasis in sporadic colon carcinomas with high-level microsatellite instability (MSI-H). DNA from 51 regions from 10 MSI-H metastatic carcinomas and 26 corresponding metastases was analyzed for mutations in TGFBRII, IGFIIR, BAX, MSH3, MSH6, and TCF4, which are associated with MSI-H carcinomas. In addition, 10 metastatic and 10 non-metastatic MSI-H carcinomas and 10 metastatic microsatellite-stable (MSS) carcinomas were examined for expression of vascular endothelial growth factor (VEGF) and mutant TP53. The frequency of microsatellite instability and somatic mutations was not significantly increased in the metastases compared with the that of primary carcinomas. Although significantly fewer MSI-H carcinomas expressed VEGF (P < 0.01) and mutant TP53 (P < 0.005) than MSS carcinomas, there was no difference in VEGF and mutant TP53 expression in metastatic and non-metastatic MSI-H carcinomas. In conclusion, metastasis does not appear to be associated with an increase in somatic mutation rate in any of the genes examined in MSI-H colon carcinomas. Furthermore, VEGF and TP53 expression did not appear to be involved in metastasis in MSI-H colon carcinomas., (Copyright 2003 Wiley-Liss, Inc.)

Although microsatellite instability (MSI) has been shown to be present in 15% of sporadic colorectal carcinomas, the genetic events underlying the development of these tumors have not been well described. By investigating intratumoral heterogeneity, this study attempts to elucidate whether MSI-positive colorectal carcinomas develop as the result of a random accumulation of mutations or as an ordered, stepwise sequence of genetic alterations. Eighty-six regions from 16 MSI-positive sporadic colorectal carcinomas were examined for mutations in repeat nucleotide sequences of the tumour suppressor genes transforming growth factor beta type II receptor (TGFBRII), insulin-like growth factor II receptor (IGFIIR), and BAX, and the mismatch repair genes MSH3 and MSH6. At least 2 and up to 5 of these genes were mutated in each tumour, and widespread intratumoral heterogeneity was observed for each gene. Regions of tumour with TGFBRII mutations were correlated with a poorly differentiated histology. Unlike the situation in microsatellite stable colorectal carcinomas, the findings of the present study did not suggest that a particular sequence of tumour suppressor and mismatch repair genes are mutated during colorectal tumorigenesis. It seems likely that a random accumulation of mutations, as a result of a defect in the mismatch repair pathway, drives tumour progression in this type of colorectal carcinoma., (Copyright 2000 Wiley-Liss, Inc.)

Individuals with chronic ulcerative colitis are at increased risk of developing colorectal carcinoma, particularly if there is long-standing disease or extensive colitis. It is generally accepted that the risk of colorectal cancer does not begin until 8 to 10 years after the time of diagnosis of ulcerative colitis. Thereafter it increases by approximately 0.5% to 1.0% per year. In patients with Crohn's disease, the risk of malignancy is smaller and less well defined. The most significant predictor of the risk of malignancy in patients with inflammatory bowel disease is the presence of dysplasia in colonic biopsies. There is considerable controversy in the literature regarding the efficacy of colonoscopic surveillance programs and the role of prophylactic surgery to prevent colorectal cancer. Surveillance certainly fails to detect carcinoma in some patients who are having regular colonoscopy. Concerns have also been raised as to the cost-benefit of colonoscopic surveillance in patients with colitis. Randomized controlled trials of surveillance programs are highly unlikely in view of the low prevalence of IBD in the population, the long period of observation required, and the probability of contamination of surveillance programs by colonoscopy for assessment of disease activity. Despite the lack of clear guidelines, surveillance colonoscopy and biopsy continues to be widely practiced. Research is proceeding to identify genetic and biochemical markers that may prove clinically useful for predicting cancer risk. At present, however, surveillance programs are likely to continue according to institutional practice. It is important for those participating in such programs to be aware of the limitations of colonoscopy and biopsy as a means of reducing the risk of cancer in inflammatory bowel disease.

Loss of function of both alleles of the APC gene results in colorectal adenoma formation in familial adenomatous polyposis, an autosomal dominant genetic disorder leading to multiple colorectal tumors at an early age. Previous molecular studies indicate that the mutant cells forming dysplastic epithelium within adenomas are clonally derived. We show, using immunostaining and molecular techniques, that the dysplastic epithelium of adenomas actually contains a mixture of cells derived from both mutant and normal stem cells. Well-differentiated mucous cells in the dysplastic epithelium, one of the indicators of severity of dysplasia, were derived from normal stem cells. Carcinomas in these patients, in contrast, contained only mutant cells, indicating that the subsequent mutations incurred by these cells have led to their isolation from the normal population.