In Situ Evidence of KRAS Amplification and Association
In Situ Evidence of KRAS Amplification and Association
Recent advances in the characterization of the lung cancer genome have suggested that KRAS may frequently be amplified, although little is known regarding the significance of this finding. This is in contrast with activating mutations of KRAS, which occur in approximately 20% of non–small cell lung carcinomas (NSCLCs).
We used fluorescence in situ hybridization to provide direct evidence of KRAS amplification for the first time in clinical specimens. We detected amplification in 7 of 100 consecutive NSCLCs, with a concurrent activating KRAS mutation in 4 cases. KRAS amplification was associated with greater expression of p21 as assessed by quantitative immunohistochemical analysis (P =.015).
Our data indicate that a sizable subgroup of NSCLCs harbor KRAS amplification, some of which also contain point mutations, and suggest that an increased KRAS copy number may drive p21 overexpression. KRAS amplification may define a unique clinicopathologic subset of NSCLCs with potentially altered responsiveness to targeted therapies.
Mutations in KRAS occur in approximately 20% of non–small cell lung carcinomas (NSCLCs), and these mutations are associated with a distinct clinicopathologic subset of NSCLC marked by a strong association with cigarette smoking, locally advanced disease, poor prognosis, and resistance to treatment with tyrosine kinase inhibitors. In contrast with KRAS mutations, which are well characterized in epithelial malignancies, KRAS amplification has a poorly defined role in tumor development and progression. Although early studies in cell lines and murine models established the possibility that amplification of wild-type RAS genes could lead to malignant transformation, the prevalence of such events in actual clinical tumor samples was not clearly established owing in large part to earlier technical constraints.
More recent studies using low-resolution, conventional comparative genome hybridization (CGH) have identified frequent copy number gains of the 12p12.1 region, including KRAS, in carcinoma of the lung, kidney, stomach, and nasopharynx, as well as in testicular germ cell tumors and gliomas. Moreover, in recent large-scale systematic assessments of the lung adenocarcinoma genome, analysis of single nucleotide polymorphism (SNP) arrays has identified KRAS copy number gains as one of the most common focal amplification events in adenocarcinoma of the lung.
In this study, we used fluorescence in situ hybridization (FISH) to provide direct visual evidence of KRAS amplification in human tumor samples for the first time. We describe the frequency of such events in a cohort of NSCLCs and provide evidence that gene amplification is associated with increased levels of the p21 gene product.
Abstract and Introduction
Abstract
Recent advances in the characterization of the lung cancer genome have suggested that KRAS may frequently be amplified, although little is known regarding the significance of this finding. This is in contrast with activating mutations of KRAS, which occur in approximately 20% of non–small cell lung carcinomas (NSCLCs).
We used fluorescence in situ hybridization to provide direct evidence of KRAS amplification for the first time in clinical specimens. We detected amplification in 7 of 100 consecutive NSCLCs, with a concurrent activating KRAS mutation in 4 cases. KRAS amplification was associated with greater expression of p21 as assessed by quantitative immunohistochemical analysis (P =.015).
Our data indicate that a sizable subgroup of NSCLCs harbor KRAS amplification, some of which also contain point mutations, and suggest that an increased KRAS copy number may drive p21 overexpression. KRAS amplification may define a unique clinicopathologic subset of NSCLCs with potentially altered responsiveness to targeted therapies.
Introduction
Mutations in KRAS occur in approximately 20% of non–small cell lung carcinomas (NSCLCs), and these mutations are associated with a distinct clinicopathologic subset of NSCLC marked by a strong association with cigarette smoking, locally advanced disease, poor prognosis, and resistance to treatment with tyrosine kinase inhibitors. In contrast with KRAS mutations, which are well characterized in epithelial malignancies, KRAS amplification has a poorly defined role in tumor development and progression. Although early studies in cell lines and murine models established the possibility that amplification of wild-type RAS genes could lead to malignant transformation, the prevalence of such events in actual clinical tumor samples was not clearly established owing in large part to earlier technical constraints.
More recent studies using low-resolution, conventional comparative genome hybridization (CGH) have identified frequent copy number gains of the 12p12.1 region, including KRAS, in carcinoma of the lung, kidney, stomach, and nasopharynx, as well as in testicular germ cell tumors and gliomas. Moreover, in recent large-scale systematic assessments of the lung adenocarcinoma genome, analysis of single nucleotide polymorphism (SNP) arrays has identified KRAS copy number gains as one of the most common focal amplification events in adenocarcinoma of the lung.
In this study, we used fluorescence in situ hybridization (FISH) to provide direct visual evidence of KRAS amplification in human tumor samples for the first time. We describe the frequency of such events in a cohort of NSCLCs and provide evidence that gene amplification is associated with increased levels of the p21 gene product.
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