High frequency of K-ras mutations in sporadic colorectal adenomas

Targeting KRAS Oncogene for Patients With Colorectal Cancer: A New Step Toward Precision Medicine

KRAS mutations are common driver oncogenes associated with the development of several solid tumors. KRAS oncogene has been considered a highly challenging target for drug development because of structural features, including the lack of deep groove on its catalytic unit. However, by leveraging cysteine residues, covalent KRAS inhibitors irreversibly trap KRAS G12C mutants in their inactive GDP-bound state. These agents have resulted in significant clinical responses among patients with KRAS G12C-mutant solid tumors, including patients with colorectal cancer (CRC). Other allele-specific inhibitors of KRAS oncogene and panKRAS and panRAS inhibitors are also currently being investigated in clinical trials. This review article overviews recent clinical progress on KRAS G12C targeting for the management of patients with KRAS G12C-mutant CRC and provides an update on other RAS targeting approaches. We also discuss the unique biological features of RAS-mutant CRC, which require the combination of KRAS inhibitors and anti-epidermal growth factor receptor therapy, and elaborate on resistance mechanisms and novel therapeutic avenues that may define future treatment paradigms of patients with RAS-mutant CRC.

Rapid Multiplex Strip Test for the Detection of Circulating Tumor DNA Mutations for Liquid Biopsy Applications

In the era of personalized medicine, molecular profiling of patient tumors has become the standard practice, especially for patients with advanced disease. Activating point mutations of the KRAS proto-oncogene are clinically relevant for many types of cancer, including colorectal cancer (CRC). While several approaches have been developed for tumor genotyping, liquid biopsy has been gaining much attention in the clinical setting. Analysis of circulating tumor DNA for genetic alterations has been challenging, and many methodologies with both advantages and disadvantages have been developed. We here developed a gold nanoparticle-based rapid strip test that has been applied for the first time for the multiplex detection of KRAS mutations in circulating tumor DNA (ctDNA) of CRC patients. The method involved ctDNA isolation, PCR-amplification of the KRAS gene, multiplex primer extension (PEXT) reaction, and detection with a multiplex strip test. We have optimized the efficiency and specificity of the multiplex strip test in synthetic DNA targets, in colorectal cancer cell lines, in tissue samples, and in blood-derived ctDNA from patients with advanced colorectal cancer. The proposed strip test achieved rapid and easy multiplex detection (normal allele and three major single-point mutations) of the clinically relevant KRAS mutations in ctDNA in blood samples of CRC patients with high specificity and repeatability. This multiplex strip test represents a minimally invasive, rapid, low-cost, and promising diagnostic tool for the detection of clinically relevant mutations in cancer patients.

CMAB009 plus irinotecan versus irinotecan-only as second-line treatment after fluoropyrimidine and oxaliplatin failure in KRAS wild-type metastatic colorectal cancer patients: promising findings from a prospective, open-label, randomized, phase III trial

Background

The 5-fluorouracil/leucovorin plus oxaliplatin (FOLFOX) regimen is the standard first-line treatment for metastatic colorectal cancer (mCRC), however, the optimal second-line regimen for KRAS wild-type mCRC patients is still investigational. In this study, we aimed to determine the clinical efficacy and safety of CMAB009 plus irinotecan compared to irinotecan-only as a second-line regimen for treating KRAS wild-type mCRC patients.

Methods

Patients with KRAS wild-type mCRC who had previously failed to respond to FOLFOX treatment were randomly assigned in a 2:1 ratio, to receive CMAB009 plus irinotecan or irinotecan-only. Patients receiving irinotecan-only were permitted to switch to CMAB009 therapy on disease progression and were grouped as the sequential-CMAB009 arm. The primary endpoints were overall response rate (ORR) and median progression-free survival (PFS). The secondary endpoints were median overall survival (OS), disease control rate (DCR), clinical benefit rate (CBR), and duration of response (DOR).

Results

The CMAB009 plus irinotecan arm demonstrated significantly improved ORR (33.2% vs. 12.8%; P < 0.001) and longer median PFS (169 days vs. 95 days; P < 0.001) as compared to the irinotecan-only arm. Patients receiving CMAB009 plus irinotecan also demonstrated improved DCR (80.1% vs. 65.2%, P < 0.001), CBR (30.0% vs. 14.6%, P < 0.001), and DOR (210 days vs. 109 days; P < 0.001) as compared to irinotecan-only. However, patients treated with CMAB009 had an increased risk of skin rash (66.9% vs. 5.5%, P < 0.001) and paronychia (9.8% vs. 0.0%, P < 0.001). Anti-drug antibodies (ADA) were detected in 3.6% of patients, and only 0.9% of patients who received CMAB009 experienced hypersensitivity reactions. In patients receiving sequential-CMAB009 therapy after failure with irinotecan, their median PFS was 84 days (95% CI 65 to 113 days). The median OS was 425 days for patients receiving CMAB009 plus irinotecan and 401 days for those with sequential-CMAB009 (P = 0.940).

Conclusions

Treatment with CMAB009 plus irinotecan was found to be a superior second-line regimen in comparison to irinotecan-only in KRAS wild-type mCRC patients. Further, switching to CMAB009 can be considered as an efficient third-line of treatment after treatment failure with second-line irinotecan-only.

Trial registration ClinicalTrials.gov: NCT01550055, retrospectively registered on March 9, 2012.

Targeting the RAS-dependent chemoresistance: The Warburg connection

RAS protein family members (KRAS4A, KRAS4B, HRAS and NRAS) function as GDP-GTP-regulated on-off switches, which regulate cytoplasmic-nuclear signaling networks ruling diverse normal cellular processes. Constitutive activating mutations in RAS genes are found in up to 30% of human cancers, and remarkably, the oncogenic Ras mutations and mutations in other components of Ras/MAPK signaling pathways seem to be mutually exclusive in most tumors, pointing out that deregulation of Ras-dependent signaling is an essential requirement for tumorigenesis. Up to 30% of solid tumors are known to have a mutated (abnormal) KRAS gene. Unfortunately, patients harboring mutated KRAS CRC are unlikely to benefit from anti-EGFR therapy. Moreover, it remains unclear that patients with KRAS wild-type CRC will definitely respond to such therapies. Although some clinically designed-strategies to modulate KRAS aberrant activation have been designed, all attempts to target KRAS have failed in the clinical assays and K-RAS has been assumed to be invulnerable to chemotherapeutic attack. Recently, different encouraging publications reported that ascorbate may have a selective antitumoral effect on KRAS mutant cancer cells. In this review we aim to describe the prevalence and importance of KRAS mutation in cancer and associated problems for the clinical handling of patients harboring these tumors. We highlight the role of mutated KRAS in boosting and keeping the tumor associated aberrant cell metabolism stating that further in-depth studies on the molecular mechanism of ascorbate to bypass mutated KRAS-related metabolic alterations may constitute a new pathway to design novel molecules in order handle tumor resistance to anti EGFR-therapies.

Clinicopathologic distribution of KRAS and BRAF mutations in a Chinese population with colorectal cancer precursor lesions

Investigating the clinical features and corresponding histomorphologic and molecular profiles of precursor lesions of colorectal cancer in a natural population provides new insights into the nature of colorectal cancer, uncovers new screening markers and establishes new prevention strategies for colorectal cancer. In this study, 4302 patients with at least one colorectal polyp from a large colorectal cancer screening program were evaluated and genetic mutations in either KRAS or BRAF were detected in 495 patients. The population-based mutation rates of KRAS and BRAF genes in colorectal polyps within this Chinese patient population were 21.8% and 12.1% respectively. Interestingly, considerable variability in the KRAS and BRAF mutations rates were found among different types of polyps. In a multivariate analysis, presence of villous histology and high-grade dysplasia was associated with KRAS mutations (OR, 3.0; 95% CI, 1.7-5.4 and OR, 3.5; 95% CI 1.9-6.5, respectively), while serrated adenomas and hyperplastic polyps were associated with BRAF V600E mutations (OR, 20.6; 95% CI, 8.2–51.8 and OR, 11.9; 95% CI 4.9–29.0, respectively). KRAS mutations may, in part, drive the histologic progression of adenomas toward a villous histology and higher grades of dysplasia. Mutant BRAF may, in part, drive the histologic progression of adenomas toward serrated histology. Dysplasia may arise from hyperplastic polyps, resulting in the formation of serrated adenomas and potentially the development of colorectal carcinoma.

DDX3 enhances oncogenic KRAS‑induced tumor invasion in colorectal cancer via the β‑catenin/ZEB1 axis

DDX3 plays a dual role in colorectal cancer; however, the role and underlying mechanism of DDX3 in colorectal tumorigenesis remains unclear. Here, we provide evidence that DDX3 enhances oncogenic KRAS transcription via an increase in SP1 binding to its promoter. Accelerating oncogenic KRAS expression by DDX3 promotes the invasion capability via the ERK/PTEN/AKT/β-catenin cascade. Moreover, the β-catenin/ZEB1 axis is responsible for DDX3-induced cell invasiveness and xenograft lung tumor nodule formation. The xenograft lung tumor nodules induced by DDX3-overexpressing T84 stable clone were nearly suppressed by the inhibitor of AKT (perifosine) or β-catenin (XAV939). Among patients, high KRAS, positive nuclear β-catenin expression and high ZEB1 were more commonly occurred in high-DDX3 tumors than in low-DDX3 tumors. High-DDX3, high-KRAS, positive nuclear β-catenin tumors, and high-ZEB1 exhibited worse overall survival (OS) and relapse free survival (RFS) than their counterparts. In conclusion, DDX3 may play an oncogenic role to promote tumor growth and invasion in colon cancer cells via the β-catenin/ZEB1 axis due to increasing KRAS transcription. We therefore suggest that AKT or β-catenin may potentially act as a therapeutic target to improve tumor regression and outcomes in colorectal cancer patients who harbored high-DDX3 tumors.

Tumor-associated DNA mutation detection in individuals undergoing colonoscopy

The majority of colorectal cancers (CRC) harbor somatic mutations and epigenetic modifications in the tumor tissue, and some of these mutations can be detected in plasma as circulating tumor DNA (ctDNA). Precancerous colorectal lesions also contain many of these same mutations. This study examined plasma for ctDNA from patients undergoing a screening or diagnostic colonoscopy to determine the sensitivity and specificity of the ctDNA panel for detecting CRC and precancerous lesions. Two hundred patients without a history of nonskin cancer had blood drawn before a colonoscopy. Plasma ctDNA was measured with a 96 mutation panel for nine cancer driver genes. The ctDNA results were correlated with the findings at colonoscopy. Of the 200 patients, 176 (88%) had wild‐type DNA, 12 (6%) had mutations detected, and 12 (6%) had indeterminate results. Colonoscopy was normal in 80% of the patients and 20% were found to have polyps. No CRC was found in this study, precluding a determination of true‐positive rate for CRC detection. Our ctDNA panel was positive in 13.2% of patients with colonic polyps found at colonoscopy, while 4.7% of patients with normal colonoscopy also had ctDNA detected, which may represent ctDNA released from a benign process, an occult tumor, or an acquired somatic mutation from clonal hematopoiesis.

Prevalence and coexistence of KRAS, BRAF, PIK3CA, NRAS, TP53, and APC mutations in Indian colorectal cancer patients: Next-generation sequencing-based cohort study

Colorectal cancer incidences are on a rise in India. In this study, we have analyzed the mutation frequencies of six potential biomarkers, their coexistence, association with clinicopathological characteristics, and tumor location in Indian colorectal cancer patients. Next-generation sequencing was performed to identify mutations in the six potential biomarker genes using formalin-fixed paraffin-embedded tissue blocks of 112 colorectal cancer patients. The mutation frequency observed in KRAS, BRAF, PIK3CA, NRAS, TP53, and APC was 35.7%, 7.1%, 16.1%, 6.3%, 39.3%, and 29.5%, respectively. The significant associations of mutations were KRAS with age less than 60 years (p = 0.041), PIK3CA with males (p = 0.032), tumor stage I-II (p = 0.013), lack of metastasis in lymph nodes (p = 0.040), NRAS with rectum (p = 0.002), and APC with T2 stage of tumor growth (p = 0.013). No single patient harbored mutations in these six genes or any five genes simultaneously. Significance was noted in coexistence of KRAS with APC (p = 0.024) and mutual exclusion of KRAS with BRAF (p = 0.029). PIK3CA exon 9 was observed to be more frequently associated with KRAS mutations than PIK3CA exon 20 (p = 0.072). NRAS mutations were mutually exclusive with BRAF and PIK3CA mutations. As per our knowledge, this is the first next-generation sequencing-based biomarker study in Indian colorectal cancer patients. Frequent coexistence of gene mutations in pairs and triplets suggests that synergistic effect of overlapping mutations might further trigger the disease. In addition, infrequent coexistence of multiple gene mutations hints toward different signaling pathways for colorectal cancer tumorigenesis.

Oncogene Mutations in Colorectal Polyps Identified in the Norwegian Colorectal Cancer Prevention (NORCCAP) Screening Study

Data are limited on oncogene mutation frequencies in polyps from principally asymptomatic participants of population-based colorectal cancer screening studies. In this study, DNA from 204 polyps, 5 mm or larger, were collected from 176 participants of the NORCCAP screening study and analyzed for mutations in KRAS, BRAF, and PIK3CA including the rarely studied KRAS exons 3 and 4 mutations. KRAS mutations were identified in 23.0% of the lesions and were significantly associated with tubulovillous adenomas and large size. A significantly higher frequency of KRAS mutations in females was associated with mutations in codon 12. The KRAS exon 3 and 4 mutations constituted 23.4% of the KRAS positive lesions, which is a larger proportion compared to previous observations in colorectal cancer. BRAF mutations were identified in 11.3% and were associated with serrated polyps. None of the individuals were diagnosed with de novo or recurrent colorectal cancer during the follow-up time (median 11.2 years). Revealing differences in mutation-spectra according to gender and stages in tumorigenesis might be important for optimal use of oncogenes as therapeutic targets and biomarkers.

Oncologists' attitudes toward KRAS testing: a multisite study

Recent discoveries promise increasingly to help oncologists individually tailor anticancer therapy to their patients’ molecular tumor characteristics. One such promising molecular diagnostic is Kirsten ras (KRAS) tumor mutation testing for metastatic colorectal cancer (mCRC) patients. In the current study, we examined how and why physicians adopt KRAS testing and how they subsequently utilize the information when discussing treatment strategies with patients. We conducted 34 semi-structured in-person or telephone interviews with oncologists from seven different health plans. Each interview was audiotaped, transcribed, and coded using qualitative research methods. Information and salient themes relating to the research questions were summarized for each interview. All of the oncologists in this study reported using the KRAS test at the time of the interview. Most appeared to have adopted the test rapidly, within 6 months of the publication of National Clinical Guidelines. Oncologists chose to administer the test at various time points, although the majority ordered the test at the time their patient was diagnosed with mCRC. While oncologists expressed a range of opinions about the KRAS test, there was a general consensus that the test was useful and provided benefits to mCRC patients. The rapid adoption and enthusiasm for KRAS suggests that these types of tests may be filling an important informational need for oncologists when making treatment decisions. Future research should focus on the informational needs of patients around this test and whether patients feel informed or confident with their physicians’ use of these tests to determine treatment access.

Tumor and its microenvironment: a synergistic interplay

The mutual and interdependent interaction between tumor and its microenvironment is a crucial topic in cancer research. Recently, it was reported that targeting stromal events could improve efficacies of current therapeutics and prevent metastatic spreading. Tumor microenvironment is a "complex network" of different cell types, soluble factors, signaling molecules and extracellular matrix components, which orchestrate the fate of tumor progression. As by definition, cancer stem cells (CSCs) are proposed to be the unique cell type able to maintain tumor mass and survive outside the primary tumor at metastatic sites. Being exposed to environmental stressors, including reactive oxygen species (ROS), CSCs have developed a GSH-dependent antioxidant system to improve ROS defense capability and acquire a malignant phenotype. Nevertheless, tumor progression is dependent on extracellular matrix remodeling, fibroblasts and macrophages activation in response to oxidative stress, as well as epithelial mesenchymal transition (EMT)-inducing signals and endothelial and perivascular cells recruitment. Besides providing a survival advantage by inducing de novo angiogenesis, tumor-associated vessels contribute to successful dissemination by facilitating tumor cells entry into the circulatory system and driving the formation of pre-metastatic niche. In this review, we focus on the synergistic effect of hypoxia inducible factors (HIFs) and vascular endothelial growth factors (VEGFs) in the successful outgrowth of metastasis, integrating therefore many of the emerging models and theories in the field.

Changing monoclonal antibody keeping unaltered the chemotherapy regimen in metastatic colorectal cancer patients: is efficacy maintained?

Monoclonal antibodies bevacizumab and cetuximab both improve overall survival (OS), progression free survival (PFS) and overall response rate (ORR) when combined with irinotecan-containing regimens. The optimal sequence of these monoclonal antibodies in combination with chemotherapy is controversial. This study analysed the efficacy of cetuximab plus Folfiri after progression with the same regimen plus bevacizumab in patients with metastatic colorectal cancer (mCRC). Patients are eligible if progressive disease (PD) after Folfiri-bevacizumab; ECOG PS 0–1. Primary endpoint is the disease control rate (DCR:ORR plus stable disease > 6 months); secondary endpoints: ORR, PFS, duration of response, OS and toxicity. ORR and DCR were reported with their confidence interval at 95%. Kaplan-Meier method was used for PFS and OS evaluation. Results: 54 patients were enrolled to receive Folfiri-cetuximab after PD to Folfiri-bevacizumab treatment. Median age was 65 (43–80), M/F 31/23, ECOG PS 0/1 was 36/ 18, WT Kras 33(61%). The DCR was 64.8% (CI 95% 52.1-77.5). Among the group of patients with stable or progressive disease at first line treatment, 13.3% of them obtained a response at second line. For second line treatment median duration of response was 6 months and clinical benefit 7 months. The ORR was 22.2% (CI 95% 11.1-33.3). The median progression-free survival was 7 months (CI 95% 6–8). The median overall survival for second line treatment was 14 months (CI 95% 11–17). No grade 4 toxicity was observed. Data suggest that this sequential combination therapy is active and well tolerated. At disease progression to first line chemotherapy treatment the maintenance of the same chemotherapy regimen and the change of the monoclonal antibody showed efficacy in response and survival in patients with mCRC.

KRAS Testing: A Tool for the Implementation of Personalized Medicine

Activating point mutations in codons 12, 13, and 61 of the KRAS proto-oncogene are common in colorectal, non-small cell lung, pancreatic, and thyroid cancers. Constitutively activated KRAS mutations are strongly associated with a resistance to anti-epidermal growth factor receptor (EGFR) therapies, such as panitumumab and cetuximab used for treating metastatic colorectal carcinoma and EGFR tyrosine inhibitors used for advanced non-small cell lung cancers. Since anti-EGFR therapies are costly and may exert deleterious effects on individuals without activating mutations, KRAS mutation testing is recommended prior to the initiation of anti-EGFR therapy for these malignancies. The goal of this review is to summarize the KRAS mutation testing methods. Testing is now routinely requested in the clinical practice to provide data to assign the most appropriate anticancer chemotherapy for each given patient. Review of the most relevant literature was performed. Several areas were considered: ordering of the test, selection of the sample to be tested, and review of the testing methodologies. We found that several different methods are used for clinical KRAS mutation testing. Each of the methodologies is described, and information is provided about their performance, cost, turnaround times, detection limits, sensitivities, and specificities. We also provided "tips" for the appropriate selection and preparation of the sample to be tested. This is an important aspect of KRAS testing for clinical use, as the results of the test will affect clinical decisions with consequences for the patient.

Molecular patterns in the evolution of serrated lesion of the colorectum

Colorectal cancer (CRC) mostly develops from a variety of polyps following mainly three different molecular pathways: chromosomal instability (CIN), microsatellite instability (MSI) and CpG island methylation (CIMP). Polyps are classified histologically as conventional adenomas, hyperplastic polyps, sessile serrated adenomas/polyps (SSA/P) and traditional serrated adenomas (TSA). However, the association of these polyps with the different types of CRCs and the underlying genetic and epigenetic aberrations has yet to be resolved. In order to address this question we analyzed 140 tumors and 20 matched mucosae by array comparative genomic hybridization, by sequence analysis of the oncogenes BRAF, KRAS, PI3K3CA and by methylation arrays. MSI was tested indirectly by immunohistochemistry (IHC) and a loss of MLH1, MSH2, MSH6 or PMS2 was assigned as high microsatellite instability (MSI-H), while low microsatellite instability (MSI-L) was defined as MGMT IHC negativity only. CIN was detected in 78% of all MSI-H CRCs, most commonly as a gain of chromosome 8. Methylation data analyses allowed classification of samples into four groups and detected similar methylation profiles in SSA/P and MSI-H CRC. TSA also revealed aberrant methylation pattern, but clustered more heterogeneously and closer to microsatellite stable (MSS) CRCs. SSA/P, TSA and MSI-H CRCs had the highest degree of promotor methylation (CIMP pathway). Chromosomal instability, in contrast to the established doctrine, is a common phenomenon in MSI CRCs, yet to a lower extent and at later stages than in MSS CRCs. Methylation analyses suggest that SSA/P are precursors for MSI-H CRCs and follow the CIMP pathway.

Ras in cancer and developmental diseases

Somatic, gain-of-function mutations in ras genes were the first specific genetic alterations identified in human cancer about 3 decades ago. Studies during the last quarter century have characterized the Ras proteins as essential components of signaling networks controlling cellular proliferation, differentiation, or survival. The oncogenic mutations of the H-ras, N-ras, or K-ras genes frequently found in human tumors are known to throw off balance the normal outcome of those signaling pathways, thus leading to tumor development. Oncogenic mutations in a number of other upstream or downstream components of Ras signaling pathways (including membrane RTKs or cytosolic kinases) have been detected more recently in association with a variety of cancers. Interestingly, the oncogenic Ras mutations and the mutations in other components of Ras/MAPK signaling pathways appear to be mutually exclusive events in most tumors, indicating that deregulation of Ras-dependent signaling is the essential requirement for tumorigenesis. In contrast to sporadic tumors, separate studies have identified germline mutations in Ras and various other components of Ras signaling pathways that occur in specific association with a number of different familial, developmental syndromes frequently sharing common phenotypic cardiofaciocutaneous features. Finally, even without being a causative force, defective Ras signaling has been cited as a contributing factor to many other human illnesses, including diabetes and immunological and inflammatory disorders. We aim this review at summarizing and updating current knowledge on the contribution of Ras mutations and altered Ras signaling to development of various tumoral and nontumoral pathologies.

The role of oncogenes in gastrointestinal cancer

Oncogene research over the last century has been one of the major advances in understanding the molecular biology of malignant disease. Oncogenes are a structurally and functionally heterogeneous group of genes, whose protein products act pleiotropically and affect multiple complex regulatory cascades within the cell. They regulate cell proliferation, growth, and differentiation, as well as control of the cell cycle and apoptosis. The products of oncogenes include growth factors, growth factor receptors, signal transducers, transcription factors, and apoptosis regulators, as well as chromatin remodelers. Several distinct mechanisms have been described for the conversion of proto-oncogenes to active oncogenes. Quantitative forms of oncogene activation include multiplication (gene amplification) or translocation to an active chromatin domain that brings a growth-regulatory gene under the control of a different promoter, causing inappropriate expression of the gene. Qualitative forms include either point mutations or the production of a novel product from a chimeric gene. Further understanding of the molecular mechanisms by which oncogenes regulate normal development and tumorigenesis may lead to novel concepts in the diagnosis and treatment of cancer in humans. In this review, we focus on the role of selected oncogenes in gastrointestinal cancer.

Cetuximab plus FOLFOX6 or FOLFIRI in metastatic colorectal cancer: CECOG trial

AIM: To investigate efficacy and safety of cetuximab combined with two chemotherapy regimens in patients with unresectable metastatic colorectal cancer (mCRC).

METHODS: Randomized patients received cetuximab with 5-fluorouracil (5-FU), folinic acid (FA) and oxaliplatin (FOLFOX) 6 (arm A, n = 74) or 5-FU, FA and irinotecan (FOLFIRI) (arm B, n = 77). KRAS mutation status was determined retrospectively in a subset of tumors (n = 117).

RESULTS: No significant difference was found between treatment arms A and B in the progression-free survival (PFS) rate at 9 mo, 45% vs 34%; median PFS, 8.6 mo vs 8.3 mo [hazard ratio (HR) = 1.06]; overall response rate (ORR) 43% vs 45% [odds ratio (OR) = 0.93] and median overall survival (OS), 17.4 mo vs 18.9 mo (HR = 0.98). Patients with KRAS wild-type tumors demonstrated improved PFS (HR = 0.55, P = 0.0051), OS, (HR = 0.62, P = 0.0296) and ORR (53% vs 36%) and in arm A, improved PFS (HR = 0.49, P = 0.0196), OS (HR = 0.48, P = 0.0201) and ORR (56% vs 30%), compared with patients with KRAS mutated tumors. In arm B no significant differences were found in efficacy by KRAS mutation status. Treatment in arms A and B was generally well tolerated.

CONCLUSION: This study confirms that combinations of cetuximab with FOLFOX6 or FOLFIRI are effective and significantly improve clinical outcome in KRAS wild-type compared with KRAS mutated mCRC.

A rapid PCR ELISA for the detection of activated K-ras in colorectal cancer

Aims-To develop a rapid PCR ELISA procedure for the detection of mutations in K-ras in a microtitre plate format, and to evaluate the assay for the detection of these mutations in human colorectal cancer.Methods-An enriched PCR method was used with labelled primers, and PCR product was captured on GCN4 coated immunoassay plates. Detection of biotinylated mutant product was performed by colorimetric assay with streptavidin-horseradish peroxidase. The assay was used to determine K-ras status in a series of 60 human colorectal neoplasms, together with paired normal colonic mucosa. Results from gel electrophoretic analysis were compared with ELISA results.Results-The assay proved reliable in detecting K-ras mutations in DNA extracted from both fresh and paraffin embedded colorectal tumours. ELISA results were comparable with results from gel electrophoresis. Mutations of K-ras were detected in 16 of 48 adenocarcinomas and five of 12 adenomas but no mutations were detected in normal mucosa. There was a highly significant difference (p<0.0005) between optical density values for carcinomas with mutant K-ras and their paired normal data. Adenomas did not show the clear distinction between positive and negative results seen with carcinomas.Conclusions-This assay provides a rapid and reliable means of detecting mutations in codon 12 of the K-ras oncogene. The single tube format colorimetric analysis in microtitre plates and clear discrimination between mutant and wild type genes makes the assay suitable for automation. The occurrence of intermediate results in the case of adenomas provides support for the hypothesis that mutations of K-ras occur early in the course of colorectal carcinogenesis.

Implications of KRAS mutation status for the treatment of metastatic colorectal cancer

Targeted agents have become an integral part of the treatment of a number of malignant diseases and regimens containing agents that disrupt the epidermal growth factor receptor (EGFR) signaling pathway are now considered a standard therapeutic approach for a range of tumor types. Recently, the mutational status of the KRAS gene in tumors was shown to be predictive of outcome to treatment with EGFR-targeted therapies in metastatic colorectal cancer (mCRC). The immoglobulin (Ig) G1 EGFR-targeting monoclonal antibody (mAb), cetuximab, has been shown to provide significant clinical benefits when added to standard irinotecan- and oxaliplatin-containing chemotherapy regimens, first-line, in patients with KRAS wild-type mCRC. Its effects on tumor response and resectability of metastases make cetuximab a particularly useful treatment option for patients with bulky or initially unresectable disease. With an ever-increasing array of management options available, it is important that patients with mCRC receive the treatment that offers them the best chance of prolonged survival. In view of this, testing for tumor KRAS mutation status should be mandatory at diagnosis of mCRC, prior to treatment decision-making.

Cetuximab and chemotherapy as initial treatment for metastatic colorectal cancer

BACKGROUND

We investigated the efficacy of cetuximab plus irinotecan, fluorouracil, and leucovorin (FOLFIRI) as first-line treatment for metastatic colorectal cancer and sought associations between the mutation status of the KRAS gene in tumors and clinical response to cetuximab.

METHODS

We randomly assigned patients with epidermal growth factor receptor-positive colorectal cancer with unresectable metastases to receive FOLFIRI either alone or in combination with cetuximab. The primary end point was progression-free survival.

RESULTS

A total of 599 patients received cetuximab plus FOLFIRI, and 599 received FOLFIRI alone. The hazard ratio for progression-free survival in the cetuximab-FOLFIRI group as compared with the FOLFIRI group was 0.85 (95% confidence interval [CI], 0.72 to 0.99; P=0.048). There was no significant difference in the overall survival between the two treatment groups (hazard ratio, 0.93; 95% CI, 0.81 to 1.07; P=0.31). There was a significant interaction between treatment group and KRAS mutation status for tumor response (P=0.03) but not for progression-free survival (P=0.07) or overall survival (P=0.44). The hazard ratio for progression-free survival among patients with wild-type-KRAS tumors was 0.68 (95% CI, 0.50 to 0.94), in favor of the cetuximab-FOLFIRI group. The following grade 3 or 4 adverse events were more frequent with cetuximab plus FOLFIRI than with FOLFIRI alone: skin reactions (which were grade 3 only) (in 19.7% vs. 0.2% of patients, P<0.001), infusion-related reactions (in 2.5% vs. 0%, P<0.001), and diarrhea (in 15.7% vs. 10.5%, P=0.008).

CONCLUSIONS

First-line treatment with cetuximab plus FOLFIRI, as compared with FOLFIRI alone, reduced the risk of progression of metastatic colorectal cancer. The benefit of cetuximab was limited to patients with KRAS wild-type tumors. (ClinicalTrials.gov number, NCT00154102.)

Associations of Ki-ras proto-oncogene mutation and p53 gene overexpression in sporadic colorectal adenomas with demographic and clinicopathologic characteristics

In colorectal tumorigenesis, Ki-ras proto-oncogene mutation often occurs early in the adenoma-adenocarcinoma sequence, whereas mutation of the p53 gene is associated with late progression to carcinoma. We evaluated the relationship of demographic and clinicopathologic characteristics to Ki-ras mutation and p53 gene product overexpression in 1,093 baseline sporadic colorectal adenomas from 926 individuals enrolled in a phase III recurrence prevention trial. Ki-ras mutation was found in 14.7% of individuals and p53 overexpression was found in 7.0% of those tested. Multivariate analysis found older age, rectal location, and villous histology to be independently associated with Ki-ras mutation. Individuals with an advanced adenoma (>or=1 cm or high-grade dysplasia or villous histology) had a 4-fold higher likelihood of Ki-ras mutation [odds ratios (OR), 3.96; 95% confidence intervals (CI), 2.54-6.18]. Ki-ras mutations in codon 12 and of the G-to-A transition type were more frequent in older individuals, whereas G-to-T transversion was more frequent in rectal adenomas than in the colon. Multivariate analysis showed that previous history of a polyp (P = 0.03) was inversely associated with p53 overexpression. Large adenoma size (>or=1 cm), high-grade dysplasia, and villous histology were independently associated with p53 overexpression, with the strongest association for advanced adenomas (OR, 7.20; 95% CI, 3.01-17.22). Individuals with a Ki-ras mutated adenoma were more likely to overexpress p53 (OR, 2.46; 95% CI, 1.36-4.46), and 94.8% of adenomas with both alterations were classified as advanced (P <or= 0.0001). Our large cross-sectional study supports the role of both Ki-ras and p53 in the progression of adenomas and shows that their molecular pathogenesis differs by anatomic location, age, and mucosal predisposition as evidenced by previous history of a polyp.

Colorectal cancer: genetics of development and metastasis

It has been well documented that there are two major pathways in colorectal carcinogenesis. One is the chromosomal instability pathway (adenoma-carcinoma sequence), which is characterized by allelic losses on chromosome 5q (APC), 17p (p53), and 18q (DCC/SMAD4), and the other is a pathway that involves microsatellite instability. Recent progress in molecular biology, however, has shown that colorectal carcinogenesis is not necessarily clearly divided into these two pathways, but is in fact more complicated. Other routes, including the transforming growth factor-beta/SMAD pathway, the serrated pathway, and the epigenetic pathway, have been reported. Cross talk among these pathways has also been reported. In the invasion and metastasis steps of colorectal cancers, many more genes have now been identified as being involved in proteolysis, adhesion, angiogenesis, and cell growth. Recently accumulated evidence indicates that colorectal cancer is a genetically heterogeneous and complicated disease.

K-ras mutations in incident sporadic colorectal adenomas

BACKGROUND

Although K-ras is the most frequently mutated protooncogene in colorectal carcinoma, the specific role and timing of K-ras mutations in colorectal carcinogenesis remains controversial. In the current study, the authors investigated associations with K-ras mutation in incident sporadic colorectal adenomas that occurred during a chemoprevention trial of calcium supplementation.

METHODS

K-ras genotyping was performed on 303 colorectal adenomas that were removed from 207 participants during the follow-up phase of the Calcium Polyp Prevention Study. Mutations in codons 12 or 13 of K-ras were detected by denaturing high-performance liquid chromatography and were confirmed by direct sequencing.

RESULTS

The adenomas analyzed had a mean estimated size of 0.5 cm, and 3.0% were identified with mutations (95% confidence interval [95% CI], 1.3-4.4%). These mutations were more common in larger adenomas (risk ratio [RR], 12.7 for tumors that measured > 0.5 cm vs. < or = 0.5 cm; 95% CI, 2.7-59.7), in adenomas with more advanced histology (RR, 20.6 for tubulovillous/villous vs. tubular; 95% CI, 4.4-96.0), and in adenomas that were located in the rectum compared with the colon (RR, 8.4; 95% CI, 2.3-30.5).

CONCLUSIONS

Compared with previous studies, the current analysis was novel, because it focused on incident adenomas that were diagnosed within a few years of a previous "clean" colonoscopy. The results provided evidence for a very low rate of K-ras mutation among these small, early adenomas and strong support for a role of K-ras mutations in adenoma progression.

Mutant KRAS in aberrant crypt foci (ACF): initiation of colorectal cancer?

Since aberrant crypt foci (ACF) were first described in 1987, they have been the subjects of hundreds of papers; however, the debate continues about their role in colorectal tumorigenesis. This review focuses on the many phenotypic, genetic and epigenetic alterations in ACF that support the hypothesis that ACF are putative precursors of colorectal cancer in both humans and experimental animals. Human ACF, both with and without dysplasia, are monoclonal and display evidence of chromosomal instability. Both of these characteristics are shared by colorectal cancers. While most ACF do not have APC mutations, a large proportion has KRAS mutations and methylated SFRP1 and SFRP2 genes. This epigenetic inactivation gives rise to constitutive Wnt signaling in these putative precursors of colorectal cancer.

Oncogenic K-ras stimulates Wnt signaling in colon cancer through inhibition of GSK-3beta

BACKGROUND & AIMS

Two key genetic events underlying the development of colon cancer are activation of the K-ras and Wnt signaling pathways. We have previously shown that these 2 pathways can cooperate to regulate vascular endothelial growth factor (VEGF) gene expression. The goal of this study was to define the molecular basis for this interaction.

METHODS

The effects of K-ras(Val12) on VEGF and T-cell factor 4 (TCF-4) promoter activity, nuclear levels of beta-catenin and beta-catenin/TCF-4 complexes, glycogen synthase kinase 3beta (GSK-3beta) phosphorylation, and GSK-3beta kinase activity were measured. LY294002 and PD98059 were used to define the role of specific ras effector pathways.

RESULTS

Oncogenic K-ras up-regulated the activity of the VEGF promoter, and selective mutagenesis of TCF-4 binding sites significantly blocked this induction. K-ras(Val12) also induced the activity of a heterologous TCF-4 reporter construct in Caco-2 and HeLa cells. LY294002 and dominant negative phosphatidylinositol 3-kinase nearly completely blocked this induction. K-ras(Val12) increased the stability of beta-catenin, the levels of nuclear beta-catenin, and the formation of nuclear beta-catenin/TCF-4 complexes, and these effects were also blocked by LY294002. Finally, K-ras(Val12) inhibited the kinase activity of total cellular GSK-3beta and GSK-3beta complexed with Axin. This effect was not mediated through phosphorylation at serine 9 but did depend on phosphatidylinositol 3-kinase.

CONCLUSIONS

Our results suggest a unique cooperative interaction between 2 critical oncogenic pathways in colorectal tumorigenesis and highlight the pivotal role of GSK-3beta.

Analysis of Ki-ras and p53 gene mutations in laterally spreading tumors of the colorectum

A laterally spreading tumor (LST) is considered to be a specific subtype of superficial colorectal tumors, in view of its characteristic clinicopathological features. We attempted to compare genetic alterations found in LST (>10 mm) with those found in IIa-type adenomas (10 mm or less (small superficial elevated lesion)) and conventional polypoid adenomas (>10 mm). In addition, multiple sampling by microdissection was performed for 14 LST to examine genetic heterogeneity in the Ki-ras and p53 gene mutation patterns. Polymerase chain reaction, single-strand conformation polymorphism and direct sequencing were used to analyze Ki-ras and p53 gene mutations in 73 sporadic colorectal adenomas: 28 LST; 22 IIa-type adenomas; and 23 polypoid adenomas. Ki-ras gene mutations were found more frequently in LST (6/28 tumors) and polypoid adenomas (6/23 tumors) than in IIa-type adenomas (2/22 tumors), although this difference was not statistically significant. The frequency of p53 gene mutations in the 28 LST was 25% (7/28), which was significantly higher than that found in IIa-type adenomas (P < 0.05). However, although p53 gene mutations were found more frequently in LST than in polypoid adenomas, this difference was not statistically significant. Seven LST exhibited a combination of wild-type and mutant-type tumor cells having the p53 gene mutation pattern, whereas a pattern of different Ki-ras gene mutations was found in two of three LST that exhibited Ki-ras gene mutation heterogeneity. We suggest that the LST exhibited a characteristic pattern in terms of the Ki-ras as well as the p53 gene mutation pattern, thereby supporting the hypothesis that LST is a specific subtype of colorectal tumors.

High frequency of activated K-ras codon 15 mutant in colorectal carcinomas from Taiwanese patients

Colorectal carcinogenesis is regarded as a multistep process resulting from accumulation of genetic alterations, including activation of protooncogenes and inactivation of tumor suppressor genes via signal transduction trigger the stage-wise progression to malignancy. The reported incidence of K-ras mutation detected in general tissue samples ranges from 21-60% in primary colorectal cancers (CRC). To assess the prevalence and spectrum of K-ras mutations in Taiwanese patients with CRC, we analyzed 65 CRC patients by polymerase chain reaction-single strand conformation polymorphism analysis, followed by direct sequencing. K-ras mutations were detected in 43.1% (28 of 65) of the tumors. The mutational hot spots were located at codons 12, 13, 15 and 20, especially with the highest frequency at codon 15. To understand whether the codon 15 mutations in CRC were associated with activation of K-ras oncogene and the alterations of its biocharacteristics, mutant K-ras genes were cloned from tumor tissues and then inserted into expression vector pBKCMV to construct the prokaryotic expression plasmid pK15MCMV. Mutant K-ras genes were expressed at high levels in E. coli and the mutant K-ras proteins were shown to be functional with respect to their well-known specific, high-affinity, GDP/GTP binding. The purified K-ras protein from E. coli was then measured for its intrinsic GTPase activity and the extrinsic GTPase activity in the presence of GTPase-activating protein for ras. We found that the extrinsic GTPase activity of the codon 15 mutant K-ras proteins (p21(K-ras15M)) in the presence of GAP is much lower than that of the wild-type K-ras protein (p21 BN), whereas the intrinsic GTPase activity is nearly the same as that of the wild-type K-ras protein. The results indicated that mutation at the codon 15 of K-ras gene indeed decreased GTPase activity in CRC, however, its association with tumorigenesis of CRC needs be clarified by further studies.

Deregulation of E-cadherin-catenin complex in precancerous lesions of gastric adenocarcinoma

BACKGROUND AND AIM

Decrease in expression of the E-cadherin-catenin complex is an important element in gastric carcinogenesis. However, the expression of the complex in gastric precancerous lesions has not been well studied. The present study aimed to examine the serial change in expression of E-cadherin-catenin complex in the precancerous lesions of gastric cancer patients.

METHODS

Gastrectomy specimens of 40 patients with gastric cancer were retrieved. Areas with chronic gastritis, atrophic gastritis, intestinal metaplasia and adenocarcinoma were identified and immunostained for alpha-catenin, beta-catenin and E-cadherin. The results were scored semiquantitatively by two independent pathologists using a validated scoring system.

RESULTS

A significant decrease in score was observed in 5% (1/22) of alpha-catenin, 0% (0/22) of beta-catenin and 9% (2/22) of E-cadherin in chronic atrophic gastritis patients, and in 28% (5/18) of alpha-catenin, 67% (10/15) of beta-catenin and 57% (8/14) of E-cadherin in intestinal metaplasia patients. The scoring of alpha-catenin, beta-catenin and E-cadherin correlated with each other. Forty-three percent of patients had concordant changes of scores along the gastritis-adenocarcinoma sequence. There was no association between Helicobacter pylori status and E-cadherin-catenin complex expression.

CONCLUSION

Deregulation of the E-cadherin-catenin complex was observed in the majority of precancerous lesions in patients with gastric adenocarcinoma, which has potential diagnostic and therapeutic implications.

Genetic and protein markers related to in situ growth and multiplicity in small sporadic colorectal adenomas

BACKGROUND

Some early genetic events in the development of colorectal adenomas are known, but their relationship to in vivo growth characteristics is uncertain. This study compared in situ size changes and other clinicopathological variables with selected genetic and protein markers.

METHODS

56 adenomas (< or = 10 mm) from 39 patients were analysed for APC, CTNNB1 and K-ras mutations, allelic imbalance on 1p and 18q, microsatellite instability and immunohistochemical expression of HLA-DR, BAX, BCL-2 and Ki-67. For 42 of the adenomas, in situ growth was measured over 3 years. The total number of polyps in each patient was recorded.

RESULTS

K-ras was mutated in 8/56 adenomas. None of the regressing adenomas revealed such mutations, compared to 20% in those that maintained or increased their size. Multivariate linear regression analysis showed that tumour growth was higher in females compared to males, and was even higher in the presence of a K-ras mutation. APC mutations were found in 37/56 adenomas. CTNNB1 mutations were found in 2/19 adenomas without APC mutation. Deletions of 1p were found in 12/56 adenomas and, seemingly, most frequent in patients with few tumours. The most frequently expressed protein was BAX (33/41), but neither this nor the other proteins showed associations with an in situ growth pattern.

CONCLUSION

The multivariate linear regression model showed that patient gender and the presence of K-ras mutation had significant effects on tumour growth. The lack of the proliferative stimulus resulting from a K-ras mutation may contribute to the process of adenoma regression.

Detection of genetic abnormalities in neoplasms from Greek patients with FAP

AIMS

DNA microsatellite instability is a well-known feature of hereditary non-polyposis colon cancer; however, its incidence in familial adenomatous polyposis, is unclear. We report the frequency of microsatellite instability and other genetic abnormalities in a group of Greek patients with FAP, in relation to various clinicopathological variables.

METHODS

Thirty-four tissue specimens from 10 patients with FAP were studied. Microsatellite instability was investigated at six loci: BAT25, BAT26, D2S123, D5S346, D17S250 and TGF-beta RII poly(A) tract. p53 and K-ras mutations were also examined.

RESULTS

Microsatellite instability was detected in two FAP adenocarcinomas from different patients. Mutation percentages observed were: in K-ras 45% and 50% and in p53 14% and 58%, of FAP adenomas and adenocarcinomas, respectively. No K-ras or p53 mutations were determined in the two microsatellite instable adenocarcinomas.

CONCLUSION

Microsatellite instability is detectable in a small proportion of adenocarcinomas complicating FAP. This minority of cases may constitute a distinct subgroup among FAP neoplasms.

K-ras mutations in sporadic colorectal tumors in Israel: unusual high frequency of codon 13 mutations and evidence for nonhomogeneous representation of mutation subtypes

Colorectal cancer is one of the most common malignancies in the western world, including Israel. An important step in progression includes induction of activating mutations in the protooncogene K-ras. This event is very frequent and is detected in about 40% of colorectal carcinomas. Previous studies of a variety of genetic disorders revealed unique gene mutation prevalence in Jewish populations, attributed both to differences in genetic background and to variability in environmental exposure. To determine the incidence and molecular subtypes of K-ras mutations in colorectal cancer in Israel, compared with other countries, DNA was isolated from a random collection of 105 colorectal carcinoma samples, and K-ras mutations were detected by an improved designed RFLP and direct sequencing. K-ras sporadic mutations in colorectal cancer in Israel are relatively frequent, with a higher fraction in codon 13 than reported thus far. Comparison with other countries shows a vast heterogeneity in terms of the relative abundance of the affected K-ras codon and in type and representation of specific mutations. The heterogeneous distribution found may be due to a variable genetic background and different environmental factors involved in the initiation and propagation of sporadic colorectal cancer.

Not infrequent K-ras mutations in depressed-type early colorectal carcinomas larger than 10 mm

The aim of this study was to elucidate whether K-ras (codons 12 and 13) mutations occur in depressed-type early colorectal carcinomas (DECas) larger than 10 mm in size. Thirty-four cases of DECas including 27 larger than 10 mm were examined for K-ras mutations by means of microdissection, PCR-RFLP (polymerase chain reaction-restriction fragment length polymorphism), and direct sequencing. Although K-ras mutation was infrequent (1/7, 14%) in small (less than 10 mm) DECas, 16/27 (59%) and 17/27 (63%) of DECas larger than 10 mm revealed codon 12, or either codon 12 or 13 mutations, respectively. None of the evaluated pathological factors except size showed a correlation with K-ras mutation. These data indicate that although K-ras mutation could not be involved in the early stage of the progression of DECas, it might play a role at a later stage when the tumor size is over 10 mm.

Detection of genetic alterations in the p53 suppressor gene and the K-ras oncogene among different grades of dysplasia in patients with colorectal adenomas

BACKGROUND

Although it is believed that p53 suppressor gene mutations, compared with mutations in the K-ras oncogene, occur at a later stage of colorectal tumorigenesis, the distribution of these genetic alterations at an early stage remains poorly characterized.

METHODS

The authors analyzed the immunoreactivity for p53 protein (p53 protein expression), which reflects the functionally altered p53 gene, and K-ras mutations at codons 12 in 68 colorectal adenomas with both low-grade and high-grade dysplasia obtained from 62 patients.

RESULTS

The prevalence of p53 positive immunostaining was significantly greater compared with the prevalence of K-ras mutations both in low-grade dysplasia and in high-grade dysplasia. Twenty-two adenomas (32.3%) showed positive immunostaining for p53 protein in high-grade dysplasia and also were positive for p53 in surrounding low-grade dysplastic tissues; 20 adenomas (29.4%) showed positive immunostaining for p53 protein in high-grade dysplasia and were negative for p53 in surrounding low-grade dysplastic tissues; 8 adenomas (11.7%) showed negative immunostaining for p53 protein in high-grade dysplasia and were positive for p53 in surrounding low-grade dysplastic tissues; and 18 adenomas (26.4%) showed negative immunostaining for p53 protein in both high-grade dysplasia and in surrounding low-grade dysplastic tissues. On the whole, a significant difference (P < 0.05) was seen in the frequency of p53 positive immunostaining between low-grade dysplasia and high-grade dysplasia (44.1% and 61.8%, respectively) but not in that of K-ras mutations (20.3% and 23.4%, respectively).

CONCLUSIONS

The results of this study suggest that mutation of the p53 suppressor gene occurs earlier in the adenoma-carcinoma sequence than K-ras mutation, providing a clue for further understanding of the role of the p53 gene in the early stage of colorectal tumorigenesis.

Analysis of K-ras, APC, and beta-catenin in aberrant crypt foci in sporadic adenoma, cancer, and familial adenomatous polyposis

BACKGROUND & AIMS

We have previously shown that aberrant crypt foci (ACF) are the putative precursor lesions of colorectal adenomas and subsequent cancer in humans using magnifying endoscopy. The present study was designed to investigate these genetic alterations in ACF biopsy specimens from normal subjects, familial adenomatous polyposis (FAP) or sporadic patients.

METHODS

The non-FAP cases included 34 normal subjects, 35 colorectal adenoma patients, and 19 colorectal cancer patients; there were 4 FAP patients. Biopsies were performed on ACF by magnifying endoscopy. K-ras mutations were analyzed by 2-step polymerase chain reaction and restriction fragment length polymorphism, APC mutations by in vitro-synthesized protein assay, and beta-catenin mutations by direct sequencing. Full-length APC and beta-catenin were detected by immunofluorescence.

RESULTS

In non-FAP cases, K-ras mutations were detected in 82% (89/106) of nondysplastic ACF and 63% (17/27) of dysplastic ACF. APC mutation and beta-catenin accumulation were not detected in non-FAP ACF, whereas in adenoma of these patients, positivity of APC mutation and beta-catenin accumulation were 78% (24/31), and that of K-ras mutation was 65% (20/31). FAP patients showed K-ras mutations in only 13% (1/8) of dysplastic ACF, which is the predominant form of ACF found in FAP. In FAP patients, somatic APC mutations were found in 100% of dysplastic ACF, as they are in adenoma. The frequency of K-ras mutations was 73% (8 of 11) in FAP adenoma.

CONCLUSIONS

The data suggest that in sporadic colorectal carcinogenesis, assuming the biological implication of ACF as a precursor of adenomas, there is a route where K-ras mutation mainly occurs during the formation of ACF, which then become adenomas wherein APC mutation occurs. In FAP, however, somatic mutation of APC predominantly occurs during ACF formation, followed by K-ras mutation.

Ki-ras proto-oncogene mutations in sporadic colorectal adenomas: relationship to histologic and clinical characteristics

BACKGROUND & AIMS

[corrected] The goal of this study was to examine the relationship between Ki-ras mutations in colorectal adenomas and characteristics of both the subject (age, gender, and family/personal history of colonic neoplasia) and the adenoma (multiplicity, size, location, and histologic features).

METHODS

Ki-ras mutations were detected by direct sequencing in 738 adenomatous polyps removed at baseline from 639 participants in a nutritional trial of adenoma recurrence.

RESULTS

Ki-ras mutations were detected in 17.2% of the adenomas. Ki-ras mutations were unrelated to gender, family, or personal history of colonic neoplasia, location within the colorectum, or adenoma multiplicity, but were more common in older subjects (P = 0.01 for trend), in larger adenomas (P < 0.0001 for trend), in adenomas with villous histology (odds ratio [OR], 3.2; 95% confidence interval [CI], 2.1-4.9 vs. tubular), and in adenomas with high-grade dysplasia (32.0% vs. 13.6%; OR, 3.0; 95% CI, 1.9-4.6 vs. low-grade dysplasia). Multivariate analysis showed Ki-ras mutations to be independently associated with subject age (P = 0.01 for trend), tubulovillous/villous histology (OR, 2.3; 95% CI, 1.5-3.7), and high-grade dysplasia (OR, 1.9; 95% CI, 1.2-3.1). Adenoma size was not independently related to Ki-ras mutation.

CONCLUSIONS

Ki-ras mutations are associated with the histologic features of adenoma progression (villous histology and high-grade dysplasia) rather than with adenoma growth.

Molecular changes in the Ki-ras and APC genes in colorectal adenomas and carcinomas arising in the same patient

The purpose of this study was to compare the molecular genetic changes in the Ki-ras and adenomatous polyposis coli (APC) genes between adenomas and carcinomas removed from the same patients. This comparison of benign and malignant tissue would enhance understanding of the progression of molecular changes during the development of colorectal malignancy and similarities between paired lesions could be indicative of a common aetiology. The basic procedures used were DNA extraction from wax blocks of removed tissue, followed by polymerase chain reaction (PCR) and gel electrophoresis for mutations in the Ki-ras gene using single strand conformational polymorphism (SSCP); amplification of a CA repeat marker was used to assess for loss of heterozygosity (LOH) of the APC gene. The main findings in 100 adenoma and carcinoma pairs for the Ki-ras gene were as follows: the frequency of Ki-ras mutation in the adenomas increased with increasing villous component, but did not vary in the paired carcinomas; the frequency of Ki-ras mutation in villous adenomas was greater than in carcinomas; and when both paired lesions had Ki-ras mutations, only 44% had the identical mutation. For the APC gene, the incidence of LOH in the adenomas did not vary by histological type; the LOH status of the adenoma was associated with that of the paired carcinoma; but when both paired lesions had LOH of the APC gene, only 50% had LOH for the same allele. In conclusion, these data on paired adenomas and carcinomas suggest that a Ki-ras mutation is not a consistent finding between the adenoma and carcinoma from the same bowel. The development of LOH of the APC gene is a slightly more consistent finding between the pair, but is not always allelic-specific.

No major difference in K-ras and p53 abnormalities in sporadic and hereditary nonpolyposis colorectal adenomas

K-ras and p53 gene mutations are known to occur in high frequencies in sporadic colorectal cancers, but findings are inconsistent in hereditary nonpolyposis colorectal cancer (HNPCC). We compared K-ras codon 12 and 13 gene mutations and p53 protein overexpression in 48 HNPCC (positive for Amsterdam criteria) and 59 sporadic colorectal adenomas, to examine whether they may represent similar or different molecular pathways to cancer. In sporadic adenomas K-ras mutations were detected in 32% and p53 overexpression in 31% of the cases. Similarly, K-ras mutations and p53 overexpression were both found in 25% of HNPCC adenomas. The frequencies of these abnormalities were not significantly different between HNPCC and sporadic adenomas. When taking differences in adenoma size into account, the frequencies were even more similar. In conclusion, these results suggest a similar molecular pathway to adenomas in HNPCC and sporadic carcinogenesis, with respect to involvement of K-ras and p53.

Utilization of K-ras mutations identified in stool DNA for the early detection of colorectal cancer

Colorectal cancer is one of the most common malignancies in the western world. About 60,000 Americans die of colorectal cancer each year. The annual incidence rate in Israel is 40 per 100,000 persons, namely a total of 2,000 new cases each year. An important step in the progression of colorectal cancer includes induction of activating mutations in the proto-oncogene K-ras. The mutations in K-ras appear early during tumorigenesis, at the intermediate adenoma stage, and thus can be used as a biomarker for early detection in about 40% of colonic tumors. A large yet unknown number of mutated cells are shed from the developing tumor during its progression. Indeed, K-ras mutations were detected in DNA isolated from stool obtained from symptomatic and asymptomatic patients with colorectal cancer, suggesting a novel approach for a noninvasive screening procedure. However, severe difficulties in obtaining reproducible yields of amplifiable DNA from stool, and usage of nonquantitative, time-consuming procedures, hampered further progress in the utilization of K-ras mutations for the early detection of colorectal cancer. Apparently a novel protocol is required that provides reproducible output of amplifiable DNA from small amounts of stool, detects if K-ras mutated DNA is present, and determines the quantity of K-ras mutated cells in the stool sample. In addition, this protocol should be simple, robotics compatible, and thus suitable for cost-effective, large-scale mutation screening. Molecular assays for detecting K-ras mutations and additional biomarkers in stool DNA promise to be highly sensitive, specific, and cost-effective. As such they should be very effective when used in chemoprevention studies and screening protocols for colorectal cancer.

Inhibition of rat colon tumors by sulindac and sulindac sulfone is independent of K-ras (codon 12) mutation

Nonsteroidal anti-inflammatory drug (NSAID) use reduces the risk of colorectal cancer by 40-50%. Previous studies suggest that effective inhibition of colorectal cancer by NSAIDs may be dependent on the presence or absence of a K-ras mutation. This study was aimed at determining the relationship between inhibition of colorectal cancer by sulindac and sulindac sulfone and the presence of activating K-ras mutations in the 1,2-dimethylhydrazine dihydrochloride rat model. Sulindac (20 mg x kg(-1) x day(-1)), sulindac sulfone (40 mg x kg(-1) x day(-1)), or vehicle was administered orally to male Sprague-Dawley rats for a 4-wk period beginning 20 wk after tumor induction. Tumor number and volume were measured before treatment by laparotomy and colonoscopy and again after treatment. Sulindac and sulindac sulfone treatment significantly reduced the number and volume of colorectal tumors compared with control rats. For K-ras (codon 12) mutation detection, frozen tumor tissue was collected at the endpoint. We found K-ras codon 12 mutations in 11 of 21 (52%) control tumors. The proportion of tumors with K-ras mutations in the sulindac-treated group [5 of 8 (62%); odds ratio = 1.51 (95% confidence interval = 0.29, 8.33)] and the proportion of sulindac sulfone-treated tumors [9 of 14 (64%); odds ratio = 1.63 (95% confidence interval = 0.41, 6.66)] were not significantly different from controls. Tumor inhibition did not correlate with K-ras (codon 12) mutation status, which suggests that the mechanism of inhibition of rat colorectal cancer by sulindac and sulindac sulfone is independent of K-ras mutation.

Villous, hypermucinous mucosa in long standing ulcerative colitis shows high frequency of K-ras mutations

BACKGROUND

K-ras mutation is one of the first genetic alterations in classical colorectal carcinogenesis.

AIMS

To investigate the role of K-ras mutations in carcinogenesis, in long standing ulcerative colitis.

METHODS

A total of 161 microdissected and 100 DNA samples from 13 patients were analysed for K-ras codons 12 and 13 mutations by means of a combination of enriched polymerase chain reaction amplification and temporal temperature gradient electrophoresis.

RESULTS

K-ras mutations were found in 21/161 (13%) microdissected samples in 7/13 large bowels (16 and five in codons 12 and 13, respectively), and in 10/100 (10%) mucosal DNA samples (six and four, respectively). One of four patients with six adenocarcinomas had a K-ras mutation in a carcinoma, as well as one of two patients with large dysplasia associated lesion or mass (DALM). Eight of 13 (61%) areas with villous architecture and large, distended goblet cells, had a K-ras mutation, which was significantly more frequent than in low grade dysplasia (one of 23, 4%) but did not reach significance versus high grade dysplasia (four of 14, 28.5%). K-ras mutations were found in one of 20 (5%) flat lesions indefinite for dysplasia, two of 14 (14%) in non-villous, hypermucinous mucosa, and in one of 57 flat areas negative for dysplasia.

CONCLUSION

The highest K-ras mutation frequency was found in villous, hypermucinous mucosa. We suggest that this entity should be investigated further as a potential risk lesion for cancer development. It may represent a pathway directly from non-classical dysplasia to cancer, not previously described.

Genetic epidemiology of mutated K-ras proto-oncogene, altered suppressor genes, and microsatellite instability in colorectal adenomas

BACKGROUND

The genetic epidemiology of colorectal adenomas has not been studied prospectively in colonoscopy patients without cancer.

AIMS

To study genetic alterations in colorectal adenomas and correlate these with patient demographics and adenoma characteristics.

METHODS

Mutations and allelic deletions in 201 adenomas from 60 patients were compared with demographic features, adenoma characteristics, and family history.

RESULTS

The most common alteration was K-ras proto-oncogene mutation, present in 35% of adenomas and 65% of patients. Patients 65 years of age and older had a decreased probability of K-ras mutations (26% versus 45%). Overexpression of p53 gene product was present in only 6% of adenomas but was more frequent in villous or tubulovillous adenomas (19% versus 3%). Allelic loss of chromosome 18q was present in only 2% of adenomas and was significantly less frequent than p53 overexpression. DNA replication errors (RER) were present in 7% of adenomas and 15% of patients, including multiple adenomas in four patients (two with hereditary non-polyposis colorectal cancer syndrome). Only 36% of RER positive adenomas had alteration of BAT-26 alleles, none had alteration of BAT-25, and only one (8%) had mutation in the transforming growth factor beta type II receptor gene. RER positive adenomas were more likely to have a K-ras mutation. In patients with multiple adenomas, there was concordance of p53 overexpression and RER but not of K-ras mutations.

CONCLUSIONS

Genetic progression in colorectal adenomas is heterogeneous, involving factors related to patient age and the presence of RER for the occurrence of ras mutations, but different intraindividual characteristics for the occurrence of p53 alterations and RER.

Purification of total RNA from human stool samples

While colonoscopy may detect early-stage colon tumors, a less invasive and more cost-effective technique would be beneficial. Stool, which picks up sloughed-off colonic epithelial cells, would be ideal for sampling the mucosa; shed tumor cells may display alterations in gene expression observed in intact tumors. It is first necessary, however, to show that RNA can be isolated from human feces and that this RNA contains human gene transcripts. We have therefore developed a method for the isolation of total RNA from freshly passed human stool, consisting of lysis in chaotropic agents, repeated extraction with phenol and phenol-chloroform, and absorption with an RNA-binding resin. After treatment with RNase-free DNase I, we assayed these preparations for the presence of human RNA by quantitative slot blotting, northern blotting, and reverse transcription-polymerase chain reaction (RT-PCR). We obtained 5-30 microg RNA per gram of stool from cancer patients, and about 5 microg RNA per gram of control stool. Quantitative slot blotting showed that about 10% of this RNA was of human origin. Both northern blotting and RT-PCR demonstrated the presence of human RNA in these samples. To unambiguously demonstrate the isolation of RNA from stool, we incubated a mixture of rat cells and control human stool at 37 degrees C for up to 24 hr. RT-PCR of the RNA isolated from this sample clearly revealed the presence of rat-specific mRNA. These experiments indicate that RNA can be isolated from human stool and that message encoded by human genes can be assayed in these preparations. This procedure may provide a powerful tool to identify patients at risk for colon cancer.

Infrequent K-ras codon 12 mutation in serrated adenomas of human colorectum

BACKGROUND

Serrated adenoma is a new morphological subtype of colorectal adenoma. The lesion provides a distinct morphological route to carcinoma, but the underlying genetic changes have not yet been investigated.

AIMS

To determine the frequency of K-ras mutation in serrated adenoma.

METHODS

The frequency of K-ras codon 12 point mutation in 20 serrated adenomas, five atypical hyperplastic polyps, and 58 sporadic polypoid adenomas was investigated by nested polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) methods.

RESULTS

Although most of the serrated adenomas were large (average size 11.4 mm) and polypoid, K-ras codon 12 point mutation was detected in only one of the 20 (5%), which is a significantly lower frequency than that in sporadic polypoid adenomas (18/60; 30%) (p = 0.017). No mutation was detected in the atypical hyperplastic polyps. Three of 20 (15%) serrated adenomas contained a focus of carcinoma in situ, indicating their malignant potential and the existence of a serrated adenoma-carcinoma sequence, but no mutation was detected in the foci of carcinoma in situ.

CONCLUSIONS

K-ras mutation is uncommon in serrated adenomas, indicating a different spectrum of genetic alterations in these lesions from those in typical polypoid sporadic adenomas. This subtype of colorectal adenoma represents a new genetic pathway in the histogenesis of colorectal carcinoma.

The detection of K-ras mutations in colorectal cancer using the amplification-refractory mutation system

A total of 301 colorectal carcinoma (CRC) archival samples were analysed using the amplification-refractory mutation system (ARMS). Each sample was examined to determine the mutation status of codons 12 and 13 of the K-ras oncogene. The results from direct DNA sequence analysis carried out on 30 of the samples differed from the ARMS result in almost 50% of the cases as a result of the relative excess of wild-type to mutated DNA sequences. To assess the validity of the ARMS data, the polymerase chain reaction (PCR) was used to generate an amplicon from K-ras exon 1 from 23 of the samples. The PCR amplicons were cloned and sequenced, and the DNA sequence analysis of the cloned material was in agreement with the ARMS results in all but one case. This case represented a tumour that exhibited a five-nucleotide reversed inversion. The cloned sequence data confirm the sensitivity and specificity of the individual ARMS reactions and that it is possible in certain cases to detect additional, more complex, sequence variations.

Phenotypic and genotypic characteristics of aberrant crypt foci in human colorectal mucosa

Aberrant crypt foci (ACF) in colorectal mucosa are proposed to be the earliest morphological lesion in the development of neoplasia, but their characteristics remain controversial. We therefore studied the epithelial phenotype and genotype of ACF from patients with familial adenomatous polyposis (FAP) and of sporadic ACF by evaluating glycoprotein markers associated with neoplasia (lectins Dolichus biflorus agglutinin and peanut agglutinin; monoclonal antibody CA 19-9 against sialyl Lewis-a blood group substance), expression of proliferating cell nuclear antigen, and ras proto-oncogene mutations. The utility of the markers was established by comparing adenomas and hyperplastic polyps. Most FAP ACF resembled adenomas and were found to differ from sporadic ACF in their high frequency of dysplasia, staining with Dolichus biflorus agglutinin, expression of sialyl Lewis-a, proliferation in the epithelium of upper crypts, and low frequency of ras gene mutations (P = .04 to < .0000001). By contrast, sporadic ACF and a subset of FAP ACF had phenotypic characteristics resembling hyperplastic polyps but usually had ras mutations, which were inversely related to dysplasia (P = .00009). Our findings suggest that "aberrant crypt focus" is a generic term analogous to "polyp" and requires further histopathologic, phenotypic, or genotypic classification into dysplastic and heteroplastic (hetero = other, plasia = form) types. Dysplastic ACF represent potential precursors to colorectal adenomas and adenocarcinomas, but heteroplastic ACF appear to be associated, rather than precursor, lesions.

K-RAS-2 gene mutations as predictors of metachronous colorectal adenomas

BACKGROUND

Mutations of K-RAS-2 gene and tumour suppressor genes have been found in both colorectal adenomas and carcinomas. The aim of this study was to investigate the prognostic value of K-RAS-2 gene mutations found in initial colorectal adenomas for predicting the risk of metachronous adenomas.

METHODS

Genomic DNA was extracted from formalin-fixed and paraffin-embedded adenomas larger than 5 mm in diameter removed at the initial total colonoscopy between 1980 and 1982. All patients underwent colonoscopic follow-up for at least 10 years. The sequence of exon 1 of the K-RAS-2 oncogene was amplified with the polymerase chain reaction technique and screened for mutation by single-strand conformation polymorphism analysis. All suspected mutations were confirmed by direct DNA sequencing. The predictive value of K-RAS-2 gene mutations for the risk of metachronous adenomas was assessed by chi-square testing and logistic regression analysis.

RESULTS

Of 54 patients 39 (72%) were male and 15 (28%) female. At the time the initial adenoma was removed, 31 (57%) patients were younger than 60, whereas 23 (43%) were 60 years or older. Point mutations of the K-RAS-2 oncogene were found in the index adenomas of 15 (27.7%) patients. Mutations were found more frequently in large (> or = 20 mm) adenomas and in adenomas with severe dysplasia (P = 0.0011 and P = 0.0310, respectively). There were no significant associations between K-RAS-2 mutations and anatomic location, histologic type, or number of synchronous initial lesions. Mutations were found predominantly at codon 12 with transversions from GGT to GTT (57%), from GGT to GAT (36%), and from GGT to TTT (one patient). The single mutation found at codon 13 showed a transversion from GGC to GAC. There were significant associations between size (> or = 20 mm) and K-RAS-2 mutation of the initial adenomas and the size (> 5 mm) of metachronous adenomas (P = 0.0259 and P = 0.0265, respectively). However, multivariate analysis showed that K-RAS-2 mutations did not provide a significant additional contribution to the prognostic value of the size of the initial adenoma (odds ratio, 7.62; 95% confidence interval (CI), 1.68-34.48) and the amount of villous structure (odds ratio, 0.22; 95% CI, 0.05-0.90) it contained.

CONCLUSIONS

Patients with large (> or = 20 mm) adenomas and adenomas with K-RAS-2 mutations found at the initial examination have a significantly higher risk of developing large (> 5 mm) metachronous adenomas during surveillance. Multivariate analysis of initial adenoma characteristics showed that the risk of metachronous colorectal adenomas can be adequately estimated by the size and the histologic type of the largest initial adenoma and that K-RAS-2 mutations are of secondary importance only. Further studies based on a larger series will have to identify the adenoma characteristics that will help to improve follow-up strategies.