Laboratory-Clinic Interface
All about KRAS for clinical oncology practice: Gene profile, clinical implications and laboratory recommendations for somatic mutational testing in colorectal cancer

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Summary

The KRAS oncogene has been extensively studied for more than three decades, however, it is only recently that it attained a central role in the clinical decision-making process for the practicing oncologist. Recently, based on retrospective analyses of large randomized clinical trials, the use of anti-epidermal growth factor (EGFR) monoclonal antibodies, cetuximab and panitumumab, was restricted to patients with metastatic colorectal cancer that carry the “wild-type” KRAS genotype. Challenges remain in the laboratory implementation of KRAS mutational testing and the clinical application of the test for treatment planning. This review attempts to offer a global view of KRAS biology, its functional role in cell signaling, mechanisms of resistance to anti-EGFR agents and its predictive potential in metastatic colorectal cancer. We also survey the growing list of candidate biomarkers that may shortly supplement KRAS in routine clinical patient stratification. Finally, we discuss practical aspects of KRAS testing that may be useful for those involved in mutational screening in their centers. This general overview of KRAS for clinical oncology practice aims to assist in data interpretation and offer insight into potential pitfalls of mutational testing. KRAS is a prime example of how translational research can fulfill the promises of personalized medicine for tailoring treatment to match the underlying tumor biology.

Introduction

The application of molecular targeted therapeutics into daily clinical practice has surfaced the need for biomarkers for patient stratification and clinical decision-making. Predictive biomarkers, if appropriately developed, validated and employed, can identify patients who are most likely to benefit from treatment or spare patients that have tumors with ‘de novo’ resistance to a given agent from ineffective or toxic treatments. In this way they can improve clinical outcomes and assist in reducing healthcare costs.1, 2

Although research for biomarker discovery and validation has been actively pursued for many years,3 to date there are only a handful incorporated into daily oncology practice. One of the most notable is HER2 over-expression in breast cancer as assessed by immunohistochemistry or gene amplification as assessed by in situ hybridization (ISH), wherein the biomarker is both predictive of response to HER2-targeted agents and prognostic of outcome in patients not treated with anti-HER2 therapies.2, 4 More recent developments regarding small molecule tyrosine kinase inhibitors (TKIs) of the epidermal growth factor receptor (EGFR), gefitinib (IRESSA™) and erlotinib (TARCEVA™), have demonstrated the potential of using a biomarker (EGFR mutations) to guide treatment selection for non-small-cell lung cancer (NSCLC)5, 6, 7, 8, 9 and have underlined the importance of the EGFR pathway in tumor biology and drug development.

Over the last decade, with the explosion of information concerning signaling pathways that have a bearing on carcinogenesis, it has become evident that there are a number of central ‘hubs’ that reflect keys to unlocking our ability to predict response when any one particular pathway is targeted in cancer.10, 11 In the complexity of signaling pathways that exist in the cellular milieu, RAS represents such a hub.12 Today KRAS is receiving unprecedented interest following the identification of a link between KRAS somatic mutations and non-responsiveness to anti-EGFR based treatment strategies in metastatic colorectal cancer.13 Here we provide an overview of KRAS function at a molecular level, discuss practical aspects of KRAS mutational testing and offer some recommendations for its application in the clinical management of metastatic colorectal cancer patients.

Section snippets

G proteins

More than 30 years ago, the RAS gene was identified by Edward Scolnick and colleagues initially as a viral gene with oncogenic properties (Rat Sarcoma Virus) and was later characterized as a transforming gene related to carcinogenesis.14, 15, 16 It has taken some time to understand the complexities of its downstream signaling network due to the extensive cross-talk between divergent pathways. RAS belongs to the small GTP-binding (guanine triphosphate) protein super-family (G proteins). These are

Prognostic significance

Mutations of RAS family members have been identified in approximately 30% of all human malignancies. Some tumors such as pancreatic, colorectal and unknown primary cancers have high mutation rates, ranging from 40% to 90%, indicating the significance of this molecule as a target for cancer therapy.39, 40, 41 The most commonly identified mutations indentified in the KRAS gene in human solid tumors lead to aminoacid substitutions in codons 12, 13 and 61 of the KRAS protein, although mutations

Methodological aspects

Given the value of KRAS mutations for predicting benefit from anti-EGFR antibodies, and the labeling changes enforced by the EMA and the FDA, the implementation of KRAS screening in routine clinical practice is expanding. Furthermore, the constitutive signaling of RAS (in the presence of mutations) extends to include already recognized signaling pathway members that lead to similar constitutive signaling of the RAF-MEK-ERK and PI3K-AKT pathways promoting cell growth and survival in the absence

Future role of KRAS

As our understanding of resistance to anti-EGFR treatment continuous to grow, additional molecular biomarkers will soon be added to the current landscape of predictive biomarkers.

Here we predict that there may be two main approaches to treatment selection for “personalized” management: (1) through the multiplexing of specific somatic mutations in the candidate genes BRAF,62, 63 PIK3CA, PTEN63 and (2) through high-dimensional gene expression or proteomic signature approaches, possibly inclusive

Conclusions

RAS, a member of G-protein coding super-family of genes, has received much clinical attention recently, following the discovery of the therapeutic implications of its mutational status for targeted therapies directed against c-erbB proteins. There is a continued concerted effort in many countries to undertake KRAS mutational analysis. Each laboratory is addressing its particular needs, many of which are being tackled by the formation of investigator networks and international collaborations.103

Ethics and funding source

This was a literature based study and as such no ethics approval was required.

There was no funding source associated with the study design, collection, and analysis, interpretation of the data or writing of the report.

Conflict of interest

Consultant or Advisory role: Dr. S. Murray, Merck KGaA, Darmstadt, Germany. Merck distribute the MoAb Cetuximab (Erbitux®). Dr. S. Murray and Dr. P. Kosmidis, AstraZeneca, Maccelsfield, United Kingdom. AstraZeneca are proprietors of gefitinib (Iressa®). Dr. S. Murray, Amgen Thousand Oaks, CA, USA. Amgen distribute the MoAb Panitumumab (Vectibix®). No other author has a conflict of interest.

Author contributions

I.J.D., H.L., E.B., P.K., D.B., and S.M. participated in the conception and design of the study; H.L., I.J.D., G.M., S.P., and S.M. participated in the extraction, interpretation, supply, and synthesis of data. H.L., I.J.D., E.B., G.M., C.P., and S.M. participated in the writing of the report, and all authors approved the final version. No external financial support was provided for this project, and H.L., C.P., P.K., D.B., and S.M. provided administrative support. All authors approved the

Research methodology

The information for this review was obtained by searching the MEDLINE database for articles published until 1st May 2010. Electronic early-release publications were also included. We searched journals known to publish information relevant to our topic, and cross-referenced the reference lists of recovered articles. We did not impose language restrictions. Search terms included: cancer, colon, rectal, colorectal neoplasms, non-small-cell lung cancer, mutation and KRAS. Cell line and other in

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