Isocitrate dehydrogenase 1 R132C mutation occurs exclusively in microsatellite stable colorectal cancers with the CpG island methylator phenotype

The CpG Island Methylator Phenotype (CIMP) is fundamental to an important subset of colorectal cancer; however, its cause is unknown. CIMP is associated with microsatellite instability but is also found in BRAF mutant microsatellite stable cancers that are associated with poor prognosis. The isocitrate dehydrogenase 1 (IDH1) gene causes CIMP in glioma due to an activating mutation that produces the 2-hydroxyglutarate oncometabolite. We therefore examined IDH1 alteration as a potential cause of CIMP in colorectal cancer. The IDH1 mutational hotspot was screened in 86 CIMP-positive and 80 CIMP-negative cancers. The entire coding sequence was examined in 81 CIMP-positive colorectal cancers. Forty-seven cancers varying by CIMP-status and IDH1 mutation status were examined using Illumina 450K DNA methylation microarrays. The R132C IDH1 mutation was detected in 4/166 cancers. All IDH1 mutations were in CIMP cancers that were BRAF mutant and microsatellite stable (4/45, 8.9%). Unsupervised hierarchical cluster analysis identified an IDH1 mutation-like methylation signature in approximately half of the CIMP-positive cancers. IDH1 mutation appears to cause CIMP in a small proportion of BRAF mutant, microsatellite stable colorectal cancers. This study provides a precedent that a single gene mutation may cause CIMP in colorectal cancer, and that this will be associated with a specific epigenetic signature and clinicopathological features.

Characterization of tumour-infiltrating lymphocytes and apoptosis in colitis-associated neoplasia: comparison with sporadic colorectal cancer

The development of colorectal cancer is a major complication for patients with chronic idiopathic colitis. Colitis-associated tumours tend to occur at a younger age and be more aggressive than sporadic colorectal cancers. While we have previously associated the presence of tumour-infiltrating lymphocytes (TILs) and increased apoptosis in sporadic colorectal cancer with high-level microsatellite instability and improved prognosis, little is known of the relationship between these variables in colitis-associated colorectal cancer. The aim of this study was to correlate TILs and tumour cell apoptosis in colitis-associated neoplasms stratified according to microsatellite instability. Twenty tumour and 11 dysplastic samples resected from 21 patients with long-standing colitis were analysed for microsatellite instability at 10 microsatellite markers. TIL distribution (CD3, CD8) and function (granzyme B) were quantified by immunohistochemistry. Neoplastic cell apoptosis was assessed using the M30 CytoDEATH antibody. These findings were compared with 40 microsatellite stable (MSS) sporadic colorectal cancers previously evaluated for TILs and neoplastic apoptosis. Low-level microsatellite instability was found in 1/20 colitis-associated tumours. All other colitis-associated lesions were designated MSS. CD3(+) and CD8(+) TIL counts were significantly higher in colitis-associated lesions compared with MSS sporadic colorectal cancer (p < 0.0001, p = 0.001 respectively). Despite their higher TIL density, colitis-associated tumours were more likely to present late (Dukes' stage C or D) (p = 0.02). Functionally, colitis-associated TILs demonstrated significantly less granzyme B expression compared to sporadic cancers (p = 0.002). The level of tumour cell apoptosis was similar between the two groups (sporadic, 1.53%; colitis cancers, 1.45%). In conclusion, MSS colitis-associated tumours have a higher prevalence of CD3(+)/CD8(+) TILs but no associated increase in tumour cell killing by apoptosis. Unlike cytotoxic T cells in sporadic colorectal cancer, TILs do not appear to enhance the prognosis of colitis-associated colorectal cancer. This may be related to an impairment of granzyme B expression within these lesions.

A case of myoepithelial carcinoma displaying biallelic inactivation of the tumour suppressor gene APC in a patient with familial adenomatous polyposis

Familial adenomatous polyposis (FAP) is an autosomal dominant disorder caused by mutation of the APC gene. It is characterised by the appearance of hundreds to thousands of colorectal adenomas in adolescence and the subsequent development of colorectal cancer. Various extracolonic malignancies are associated with FAP, including desmoids and neoplasms of the stomach, duodenum, pancreas, liver, and brain. We present a family affected by FAP with an exon 14 APC mutation displaying two rare extracolonic lesions, a hepatoblastoma and a myoepithelial carcinoma. The hepatoblastoma was found in a male patient aged 2 years. The second lesion, a myoepithelial carcinoma of the right cheek, was found in a female patient aged 14 years. Inactivation of the normal APC allele was demonstrated in this lesion by loss of heterozygosity analysis, thus implicating APC in the initiation or progression of this neoplasm. This is the first reported case of this lesion in a family affected by FAP.

No evidence of increased risk of colorectal cancer in individuals heterozygous for the Cys282Tyr haemochromatosis mutation

BACKGROUND AND AIMS

Previous studies have suggested that increased body iron stores and heterozygosity for haemochromatosis are associated with an increased risk of colorectal carcinoma. The aim of this study is to determine if there is an association between (i) colorectal carcinoma and heterozygosity for the Cys282Tyr mutation of the haemochromatosis gene (HFE) and (ii) this mutation and tumour site or stage.

METHODS

Two hundred and twenty-nine unselected patients (127 males, 102 females, mean age 68.0 years) with sporadic colorectal carcinoma and 228 controls (145 males, 83 females, mean age 69.7 years) were studied. DNA was tested for the presence of the Cys282Tyr mutation by digestion with Rsa1 and fragments separated by electrophoresis.

RESULTS

Twenty-one patients with colorectal cancer and 23 control subjects were heterozygous for the Cys282Tyr mutation of HFE (relative risk 0.90). There was no association between heterozygosity of the Cys282Tyr mutation and tumour site or stage.

CONCLUSIONS

Heterozygosity for the Cys282Tyr mutation of HFE does not appear to be a risk factor for colorectal carcinoma.

Angiogenic factor VEGF is decreased in human colorectal neoplasms showing DNA microsatellite instability

Vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (bFGF) are two important determinants of angiogenesis in human cancers. Expression of VEGF and bFGF was examined by immunohistochemistry in 120 colorectal cancers. Neoplasms were classified according to the presence or absence of microsatellite instability determined at six microsatellite loci and labelled as a high microsatellite instability (MSI-H), low microsatellite instability (MSI-L) or microsatellite stable (MSS). Only 4/30 MSI-H cancers expressed VEGF (13 per cent), compared with 24/64 MSS cancers (38 per cent; p< 0.01). Fewer MSI-H cancers showed bFGF expression (38 per cent) than MSS cancers (53 per cent; p< 0.09). MSI-L cancers showed the same pattern as MSS cancers. Western blotting and immunohistochemistry showed that the tumour suppressor gene p53 was mutated infrequently in MSI-H cancers (8 per cent; p< 0. 001). Microvessel density counts using CD31 and UEA-1 demonstrated no difference in the number of blood vessels in MSI-H and MSS cancers. Although these results are consistent with the known role of wild-type p53 in down-regulating VEGF, no association was found between a mutation in p53 and VEGF or bFGF levels in all colonic neoplasms. This is the first evidence that MSI-H cancers may follow a different pathway to angiogenesis. The low frequency of VEGF expression amongst MSI-H cancers may partially explain why these cancers are less aggressive, with a better overall prognosis.

Severe upper gastrointestinal polyposis associated with sparse colonic polyposis in a familial adenomatous polyposis family with an APC mutation at codon 1520

BACKGROUND

Familial adenomatous polyposis usually results in colonic polyposis with hundreds to thousands of polyps, congenital hypertrophy of the retinal pigment epithelium (CHRPE), and variable extracolonic features. Recent reports indicate that patients with distal mutations between codons 1445 and 1578 do not express CHRPE and have a high incidence of desmoid tumours.

PATIENTS

The family studied has an unusual phenotype of sparse colonic polyposis but profuse upper gastrointestinal polyposis. Affected subjects do not have CHRPE.

METHODS

The protein truncation test followed by sequencing identified a 2 base pair deletion at codon 1520 in the APC gene. This results in a frameshift creating a stop codon 13 codons downstream.

RESULTS

This family demonstrates that sparse colonic polyposis but severe upper tract polyposis may be associated with mutations between codons 1445 and 1578.

CONCLUSIONS

Study of duodenal and colonic polyps in further cases with mutations in this region is warranted. Such mutations may preferentially cause duodenal adenomas and desmoid tumours as somatic mutations in these tumours also occur in this region, unlike colorectal tumours where somatic mutations occur more proximally. This study emphasises the importance of screening the upper gastrointestinal tract even when the colonic disease is mild.

Characteristics of metachronous colorectal carcinoma occurring despite colonoscopic surveillance

PURPOSE

Metachronous colorectal cancer still occurs in a small percentage of patients, despite colonoscopic surveillance. Cancers in hereditary nonpolyposis colorectal cancer for which there is a high risk of metachronous cancer show distinctive DNA changes termed replication errors (RER+). Ten to 20 percent of sporadic colorectal cancers are also RER+. The aim of this study was to identify factors predictive of metachronous colorectal cancer, despite colonoscopic surveillance. Clinicopathologic characteristics and RER status of cancers were examined.

METHODS

Colorectal cancer patients, who entered into a surveillance program of being examined with colonoscopy within six months of surgery and then at intervals of three years thereafter, were reviewed. The 433 patients compliant with the protocol who had had more than one colonoscopy had been followed up for a mean of 3.8 +/- 2.2 years. DNA was extracted from archival paraffin-embedded cancer tissue for determination of RER status.

RESULTS

Ten cases of metachronous cancer were identified, giving a rate of 0.61 percent per year. The site of the index cancer in patients who later developed metachronous cancer was predominantly proximal (P = 0.0007), and these cancers were more likely to have mucinous histology (P < 0.0005). Three of 10 (30 percent) index cancers were RER+, which was not significantly different from unselected series of control colorectal cancers in which 20 of 108 (18.5 percent) were RER+.

DISCUSSION

This study documents the rate of metachronous cancer among patients compliant with a defined colonoscopic screening program and suggests that the risk is highest in patients with a proximal mucinous cancer. RER status does not appear to be a very strong predictive factor, and this study does not support its use as a guide to the frequency of surveillance colonoscopy. More data would be required to determine if RER positivity conferred a relative risk of 3.3 or less.

Faster assay of H2 in breath by dedicated instruments compared with conventional gas chromatography

Recently available instruments dedicated to the clinical assay of hydrogen in breath were tested and the results compared with those from a conventional thermal conductivity gas chromatograph. We found the Quintron Model 12 Microlyzer and the GMI Exhaled Hydrogen Monitor to give much faster and more sensitive results than the Gow-Mac 550 conventional gas chromatograph, and their readout is digital rather than graphical. Linearity of response, accuracy, and precision were similar for all those instruments. Maintenance requirements and performance characteristics of the three instruments are compared in detail and practical advice is given on daily operation.

Faster assay of H2 in breath by dedicated instruments compared with conventional gas chromatography

Recently available instruments dedicated to the clinical assay of hydrogen in breath were tested and the results compared with those from a conventional thermal conductivity gas chromatograph. We found the Quintron Model 12 Microlyzer and the GMI Exhaled Hydrogen Monitor to give much faster and more sensitive results than the Gow-Mac 550 conventional gas chromatograph, and their readout is digital rather than graphical. Linearity of response, accuracy, and precision were similar for all those instruments. Maintenance requirements and performance characteristics of the three instruments are compared in detail and practical advice is given on daily operation.