BRAF mutations in colorectal cancer are associated with distinct clinical characteristics and worse prognosis.

BACKGROUND: Colorectal cancer is a heterogeneous disease with multiple underlying genetic mutations causing different clinical phenotypes. Mutation in the BRAF oncogene is a key step in malignant transformation within the methylator pathway to colorectal cancer. However, there is a paucity of information about BRAF mutant colorectal tumors. OBJECTIVE: This study defines the clinical characteristics and oncologic outcome associated with colorectal cancer BRAF mutations. DESIGN: Colorectal adenocarcinomas from a single-institution frozen-tumor biobank were studied. Genomic DNA was isolated and analyzed for mutations in the BRAF oncogene by polymerase chain reaction amplification followed by direct sequencing. A sample was classified as mutant if any of the tested loci were mutated. Patient and tumor characteristics were recorded including patient age, sex, tumor location, tumor differentiation, and microsatellite instability. MAIN OUTCOME MEASURES: Statistical associations with BRAF mutant tumors were determined by the Fisher exact probability test, χ test, or Wilcoxon analysis. Kaplan-Meier estimates and multivariate Cox regression analysis were performed for overall survival. RESULTS: Four hundred seventy-five colorectal adenocarcinomas were included in the study population; 56 samples harbored a BRAF mutation (12%). There were significant differences between BRAF wild-type and mutant tumors in age (66 vs 75 years, p = 0.004), female sex (44% vs 71%, p < 0.001), proximal tumor location (44% vs 95%, p < 0.001), and frequency of microsatellite instability (16% vs 76%, p < 0.001). There was no difference in cancer stage between BRAF mutant and wild-type populations. Survival data were analyzed for 322 patients with stage I to III disease, and patients with a BRAF mutation had decreased overall survival than those without a mutation (p = 0.018). With the use of Cox regression analysis, BRAF mutation conferred a worse overall survival (HR 1.79, CI 1.05-3.05, p = 0.03) independent of microsatellite instability status. CONCLUSIONS: BRAF mutations in colorectal cancers are associated with distinct clinical characteristics and worse prognosis.

Relative role of methylator and tumor suppressor pathways in ulcerative colitis-associated colon cancer.

BACKGROUND: Chronic ulcerative colitis (UC) is associated with an increased colorectal cancer risk which may be secondary to repetitive mucosal injury. Both epigenetic methylation and the classic adenoma-to-carcinoma sequence have been implicated in this malignant transformation, but the underlying molecular mechanisms remain poorly defined. This study compares the molecular characteristics of colitis-associated and common colorectal cancers. METHODS: Nineteen patients with colorectal adenocarcinomas arising within UC were matched for age and cancer site with 54 patients with sporadic adenocarcinomas. Tumor tissue was examined for BRAF mutations, CpG island methylator phenotype (CIMP), and MLH1 promoter methylation. Mutations of KRAS and p53 were assessed by sequencing. RESULTS: Patient demographics were similar for the two groups. CIMP was observed in 22% of sporadic colorectal cancers and in 5% of UC cancers (P = 0.162). Rates of BRAF mutation (4% vs 5%, P = 1.0), MLH1 methylation (9% versus 5%, P = 0.682), and KRAS mutations (24% versus 32%, P = 0.552) were similar between the groups. However, colitis-associated colorectal cancers were more likely to have a p53 mutation compared to sporadic adenocarcinomas (95% versus 53%, P = 0.001). The dominant mutation for colitis-associated cancers was a mutation in codon 4, representing half of the mutations. Furthermore, colitis-associated cancers had a higher rate of mutation in codon 8 (48% versus 6%, P < 0.001) than sporadic counterparts. CONCLUSIONS: Unlike other inflammatory gastrointestinal cancers, colitis-associated colorectal cancers do not preferentially arise via a methylator pathway when compared to sporadic colorectal cancers. Chromosomal instability remains an important etiology, but with a unique p53 frequency and mutation pattern.

CEACAM-7: a predictive marker for rectal cancer recurrence.

BACKGROUND: The identification of rectal cancer patients predisposed to developing recurrent disease could allow directed adjuvant therapy to improve outcomes while decreasing unnecessary morbidity. This study evaluates carcinoembryonic antigen cellular adhesion molecule-7 (CEACAM-7) expression in rectal cancer as a predictive recurrence factor. METHODS: A single-institution colorectal cancer database and a frozen tissue biobank were queried for rectal cancer patients. CEACAM-7 messenger RNA (mRNA) expression from normal rectal mucosa and rectal cancers was analyzed using quantitative real-time polymerase chain reaction (PCR). Expression-level differences among normal tissue, disease-free survivors, and those that developed recurrence were analyzed. RESULTS: Eighty-four patients were included in the study, which consisted of 37 patients with nonrecurrent disease (median follow-up, 170 months), 29 patients with recurrent disease, and 18 patients with stage IV disease. CEACAM-7 expression was decreased 21-fold in rectal cancers compared with normal mucosa (P = .002). The expression levels of CEACAM-7 were relatively decreased in tumors that developed recurrence compared with nonrecurrence, significantly for stage II patients (14-fold relative decrease, P = .002). For stages I-III, disease-free survival segregates were based on relative CEACAM-7 expression values (P = .036), specifically for stage II (P = .018). CONCLUSION: CEACAM-7 expression is significantly decreased in rectal cancer. Expression differences between long-term survivors and those with recurrent disease introduce a potential tumor marker to define a subset of patients who benefit most from adjuvant therapy.

Genetic and molecular diversity of colon cancer hepatic metastases.

BACKGROUND: Colon cancer arises through distinct molecular pathways resulting in diverse tumor populations demonstrated by differences in microsatellite instability (MSI), CpG island methylator phenotype (CIMP), and mutations in oncogenes KRAS and BRAF. Although these molecular differences are well-described for primary neoplasms, the molecular nature of hepatic metastases is not well-characterized. This study seeks to describe molecular characteristics of colon cancer hepatic metastases in terms of oncogenic pathway. METHODS: Tumor DNA was isolated from fresh frozen hepatic metastases from colon cancer and analyzed for MSI by polymerase chain reaction (PCR)-based microsatellite analysis and for CIMP using MethyLight quantitative PCR. KRAS and BRAF oncogenes were analyzed for DNA mutations. Metastases were classified by their molecular and genetic features. Unfortunately, tissue from the primary neoplasms from these patients were not available RESULTS: Thirty patients with liver metastases from colon cancer were studied. Molecular analysis revealed 10% (3/30) were MSI-H, 10% (3/30) were CIMP positive, 33% (10/30) had KRAS mutations, and none had BRAF mutations. Literature describing primary colon cancers reports an incidence of approximately 20% MSI-H, 20% CIMP-positive, 35% KRAS mutants, and 17% BRAF mutants. CONCLUSION: Hepatic metastases from colon cancer, like primary colon adenocarcinomas, show genetic and molecular diversity. Furthermore, hepatic metastases may have a different incidence of MSI and methylation compared with primary neoplasms. These differences could impact treatment decisions.