Written by Dr Anne-Marie Baird, Queensland University of Technology, Australia
Lung cancer is responsible for more cancer-related deaths worldwide than any other cancer type, accounting for approximately 1.37 million deaths annually1. Data from the recent National Lung Screening Trial (NLST) has demonstrated that screening high-risk smokers with low dose helical CT lead to a reduction in lung cancer mortality by approximately 20% compared with chest radiography2. Although these results are promising, there was a high rate of false positives2. A recent review by Brothers et al3 discusses these issues and provides suggestions on ‘Bridging the clinical gaps’ such as the use of screening markers. These markers could take the form of genetic, transcriptomic and epigenetic biomarkers3.
Lung cancer can arise in a dysfunctional epigenetic environment, leading to the activation of proto-oncogenes and the silencing of tumour suppressor genes, through changes in the epigenetic machinery such as histone modifications, DNA methylation and miRNA regulation amongst others4. Epigenetic associated screening biomarkers such as DNA methylation profiles could help to establish which patients should be screened, in addition to determining which suspect nodules may require surgery4, thus greatly improving the screening process.
A number of studies have been carried out in recent years examining the methylation pattern of genes, for example, in lung tissue, serum and sputum. In squamous cell carcinoma, the aberrant methylation of the promoter regions of p16 and/or MGMT (O6-methylguanine-DNA methyltransferase) in sputum was detected in all patients up to three years before a clinical diagnosis of lung cancer5. The methylation of several other genes including; DAPK (death-associated protein kinase), RASSF1A (Ras-association domain family member 1A), PAX5α/β (Paired box 5αβ), GATA4/5 (Globin Transcription Factor 4/5), SFRP1 (secreted frizzle like protein 1), LAMC2 (laminin C2), H-cadherin, IGBP3 (insulin-like growth factor receptor 3), BETA3 and HLHP (helix loop helix) have also been studied to determine their use as putative biomarkers6, 7. A number of these genes are known tumour suppressor genes and are involved in apoptosis, cell proliferation and genome stability. Belinksy et al demonstrated that the methylation of 6 of these genes in sputum (p16, MGMT, DAPK, RASSF1A, PAX5β, GATA5) was associated with >50% increased lung cancer risk7.
An additional sputum study, conducted in 2012, expanded the panel to include 23 new candidate genes8 and increased both the sensitivity (75%) and specificity (71-77%) in detecting lung cancer compared with the previous study7. This was using a seven-gene panel, which varied slightly depending on patient cohort. New genes in these panels included Dal-1 (differentially expressed in adenocarcinoma of the lung), PCDH20 (Protocadherin-20), Jph3 (Junctophilin-3), Kif1a (Kinesin-like protein), SULF2 (extracellular sulfatase) and CXCL148. Silencing of CXCL14 through promoter methylation was significantly associated with lung cancer risk.8 CXCL14 is involved in inflammatory and immuno-regulatory processes.
It is widely accepted that inflammatory lung conditions can contribute to an increased lung cancer risk9,10. DNA methylation profiles may also help to establish which patients within these groups such as those with chronic mucous hypersecretion (CMH) should undergo screening. Bruse et al 11 examined eleven genes that are commonly silenced via promoter methylation in lung cancer in sputum from CMH patients. This study found a significant association between CMH and an overall increase in the number of methylated genes including SULF211. In addition, they demonstrated that former male smokers with CMH ‘‘have increased promoter methylation of lung cancer risk genes and may be at risk from lung cancer.’’11 An encouraging recent study has refined the number of methylated genes further. Wrangle et al12 have shown that the methylation of one or any of these three genes: CDO1 (cysteine dioxygenase type 1), HOXA9 (Homeobox protein A9) and TAC1 (Protachykinin-1)in lung tissue had 100% specificity and 83-99% sensitivity for non small cell lung cancer (NSCLC): These genes are all polycomb-associated genes12. It will be of interest to assess and validate the profile of these genes in other biological samples including sputum.
While further work is needed to merge and refine candidate DNA methylation profiles, methylation gene signatures in sputum and tissue are showing great promise in early lung cancer detection. It is hoped that as these are validated and brought in to the clinical setting, these markers could enable earlier detection and staging of patients, resulting in improved survival and cure rates for lung cancer patients. Ultimately the adoption of specific and sensitive ‘screening markers’ will augment CT screening and benefit those at risk of lung cancer.
1 Health Organization. Cancer. Fact Sheet No 297. January 2013.
2 The National Lung Screening Trial Research Team (2011) Reduced Lung-Cancer Mortality with Low-Dose Computed Tomographic Screening. N Engl J Med 365:395-409.
3 Brothers J.F., Hijazi K., Mascaux C. et al (2013) Bridging the clinical gaps: genetic, epigenetic and transcriptomic biomarkers for the early detection of lung cancer in the post-National Lung Cancer Screening Trial era. BMC Medicine 11:168.
4 Baylin S.B. and Jones P.A. (2011) A decade of exploring the cancer epigenome – biological and translational implications. Nat Rev Cancer 11, 726-734.
5 Palmisano W.A., Divine K.K., Saccomanno G. et al (2000) Predicting lung cancer by detecting aberrant promoter methylation in sputum. Cancer Res 60:20:5954-8.
6 Kim C.E., Tchou-Wong K-M., and Rom W.N. (2011) Sputum-Based Molecular Biomarkers for the Early Detection of Lung Cancer: Limitations and Promise. Cancers (Basel) 3(3): 2975–2989.
7 Belinsky S.A., Liechty K.C., Gentry F.D., et al (2006) Promoter Hypermethylation of Multiple Genes in Sputum Precedes Lung Cancer Incidence in a High-Risk Cohort. Can Res 66; 3338.
8 Leng S., Do K., Yingling C.M., et al (2012) Defining a gene promoter methylation signature in sputum for lung cancer risk assessment. Clin Cancer Res 18(12):3387-95.
9 Ballaz, S. and Mulshine J.L. (2003) The potential contributions of chronic inflammation to lung carcinogenesis. Clin Lung Cancer 5(1):46-62.
10 Lee G., Walser T.C., and Dubinett S.M. (2009) Chronic inflammation, chronic obstructive pulmonary disease, and lung cancer. Curr Opin Pulm Med 15(4):303-307.
11 Bruse S., Petersen H., Weissfeld J. et al (2014) Increased methylation of lung cancer-associated genes in sputum DNA of former smokers with chronic mucous hypersecretion. Respir Res 15:2.
12 Wrangle J., Machida E.O., Danilova L. et al (2014) Functional Identification of Cancer-Specific Methylation of CDO1, HOXA9, and TAC1 for the Diagnosis of Lung Cancer. Clin Cancer Res 20:1856-1864.