The prognostic value of KRAS mutated plasma DNA in advanced non-small cell lung cancer
Introduction
Lung cancer is one of the most common cancers worldwide and associated with a high mortality rate. Treatment options are based on disease-stage and co-morbidity and comprise surgery (localised disease), radiotherapy, and palliative chemotherapy and/or biological treatment. Since most patients are diagnosed in an advanced stage, they are not eligible for curative surgery and therefore offered palliative treatment only. The possibility of identifying those patients who will benefit from the treatment is essential to avoid unnecessary toxicity and to ensure each patient the optimal treatment strategy. This requires reliable and easily accessible tumour markers, and numerous studies of different biomarkers have been performed, but so far only few have been clinically implemented.
KRAS and BRAF, part of the epidermal growth factor (EGF) system, serve as downstream mediators after the binding of EGF to the EGF-receptor (EGFR). The EGF-system is known to be involved in carcinogenesis [1] and consequently, new drugs targeting the system have been developed and are used in clinical practice. It has, though, become apparent that most patients do not respond to the treatment, and by further research different patterns of resistance have been revealed, including KRAS mutations. Activating mutations in codon 12, 13 or 61 seem to eliminate the effect of external blocking by EGF-receptor targeting antibodies (anti-EGF-mAbs). In colorectal cancer, this knowledge has led to patient selection by mutational status [2], but in NSCLC, where about 20% of the patients harbour a KRAS mutation, this effect seems less apparent [2], [3].
Another treatment strategy targeting the EGF-system includes EGFR tyrosine kinase inhibitors (TKIs). Different mutations in the EGF-receptor have been identified, most of these causing increased sensitivity to the EGFR TKIs. In lung cancer, these mutations are present in 11–17% of the patients [3], and determination of the EGFR-mutation is now considered a prerequisite to treatment with EGFR TKI inhibitors [4], [5]. Since KRAS forms part of the EGF system's downstream pathway, mutations in KRAS may also influence the effect of EGFR TKIs. Different studies have been conducted and so far it has been concluded that the presence of KRAS mutations predicts impaired response to EGFR TKIs [6]. Furthermore, a meta-analysis by Mascaux et al. confirmed the negative prognostic value of KRAS mutations in lung cancer [7].
Most studies have been based on mutation analyses of DNA derived from tumour tissue. In lung cancer the access to tissue samples is often limited, as the procedures are associated with patient inconvenience and risk of complications. Cell free DNA (cfDNA) is DNA detectable in the peripheral circulation. It was discovered in the forties and has attained increasing interest during the past years. Since cfDNA is known to partly originate from tumour cells, it may hold potential as a biomarker of cancer. A correlation between the level of cfDNA and prognosis has been demonstrated in lung- and colorectal cancer [8], but also analyses of tumour specific mutations such as KRAS and BRAF may be useful prognostic and predictive markers. The use of cfDNA thus offers an intriguing possibility of overcoming the tissue-associated problems by providing tumour-derived DNA accessible in a blood sample.
The aim of our study was to investigate the prognostic value of KRAS mutation in plasma in a homogenous cohort of patients with advanced NSCLC. Furthermore, the correlation between plasma KRAS-mutation status and response to chemotherapy was investigated.
Section snippets
Patients
During a three-year period (2007–2010) patients with advanced NSCLC were prospectively included in a biomarker trial at the Department of Oncology, Vejle Hospital, Denmark. The inclusion criteria comprised histopathologically confirmed NSCLC stage III or IV, no previous chemotherapy, performance status (PS) ≤2 and age above 18 years. A pre-treatment, peripheral venous blood sample was drawn and stored at −80 °C. All patients were subsequently treated with standard first-line chemotherapy
Patient characteristics
Patient characteristics are demonstrated in Table 1. A total of 246 patients was included. At the time of diagnosis, all patients had advanced disease and were referred to standard first-line chemotherapy. Two patients with stage II disease were not fit for surgical treatment and were thus referred to chemotherapy. In the following analyses they were included in the group with stage III disease. Mutated plasma KRAS was found in 43 (17.5%) of the patients. The correlation between patient
Discussion
The prospect of identifying tumour specific mutations in a blood sample offers an intriguing aspect of cancer management. Our results demonstrate the feasibility of identifying KRAS mutations in plasma samples and the association of these mutations with poor prognosis. The approach is appealing in many ways. Firstly, it offers easy and patient friendly access to tumour specific material, thus reducing the need for more invasive procedures. Secondly, the baseline pmKRAS seems to hold prognostic
Conclusion
In conclusion, our results strongly suggest that pmKRAS may serve as an independent, prognostic marker in advanced NSCLC. The patient friendly approach and possibility of repeated sampling throughout the disease period makes it even more suggestive in a clinical perspective offering a possibility of consecutive re-evaluation and hence individualised treatment. Independent validation of the results are called for and planned in the nearby future.
Conflict of interest statement
None declared.
Fundings
There are no funding sources to report.
Acknowledgements
We thank Yvette Schandorf Sørensen for keeping track of the blood sample collection and Anita Laier Høvenhoff for technical assistance. We thank Karin Larsen for proofreading the final manuscript.
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