Lung cancer is the most common worldwide cause of cancer mortality. Non-small cell lung cancer (NSCLC) is a highly lethal disease with cure only possible by early detection followed by surgery. Unfortunately, at the time of diagnosis only 15% of patients with lung cancer have localized disease. Field cancerization in which the lung epithelium becomes mutagenized following exposure to cigarette smoke makes it difficult to identify genetic changes that differentiate smokers from smokers with early lung cancer.
One of the most important long-term goals in improving lung cancer survival is to detect malignant tumors in high-risk patients, primarily smokers and former smokers, who represent the majority of all lung cancer cases, at an early stage, while they are still surgically resectable. Although most patients with lung cancer are smokers or ex-smokers, the actual incidence of lung cancer in this group is quite small (<0.2%). Various studies have demonstrated that the incidence of lung cancer in male cigarette smokers ranged from 0.16% (in Caucasians) to 0.26% (in African Americans). Another high-risk population is subjects with lung nodules of unknown etiology, as identified on screening chest X-rays, computerized axial tomography (CT) scans, low dose spiral CT scans, or incidentally. Currently, the only way to differentiate benign from malignant nodules is an invasive biopsy, surgery, or prolonged observation with repeated scanning.
While these methods may identify non-calcified pulmonary nodules in approximately 30% of screened smokers and ex-smokers (with a range of 13-51% of patients on prevalence screen; 2-13% on annual screen), only a small number are found to be lung cancers (0.4 to 2.7%). Thus, about 3 to 12% of subjects with detected non-calcified nodules prompt an invasive diagnostic workup. The high false positive rate of CT scanning requires patients to undergo extensive follow-up investigations with serial CT, positron emission tomography (PET scan), and/or biopsy. Studies indicate that 20-55% of patients undergoing surgical lung biopsy for indeterminate lung nodules are subsequently found to have benign disease.
One established and validated method to achieve the goal of genetic diagnosis has been the use of microarray signatures from tumor tissue. Peripheral blood mononuclear cells (PBMC) profiles can be used to diagnose and classify systemic diseases, including cancer, and to monitor therapeutic response. The validity of using PBMC gene expression profiles in patients with cancer has been previously reported in the use of microarrays to compare PBMC from patients with late stage renal cell carcinoma compared to normal controls. A 37 gene classifier has been developed for detecting early breast cancer from peripheral blood samples with 82% accuracy. Another study identified gene expression profiles in the PBMC of colorectal cancer patients that could be correlated with response to therapy.
While the effect of chronic obstruction pulmonary disease (COPD) on PBMC gene expression is relatively unstudied to date, there are some limited reports about the effect of cigarette smoke. Exposure of peripheral blood lymphocytes (PBL) ex vivo to cigarette smoke induced many changes in gene expression. Changes could be detected in the transcriptosome of blood neutrophils in COPD patients versus normals. Gene expression in airway epithelia of smokers, ex-smokers and non-smokers has been compared. Although many clinical manifestations of smoking rapidly returned to normal after smoking cessation, there was a subset of genes whose expression remained altered.
MicroRNAs (miRNAs) are a large group of ribonucleic acid sequences, isolated and identified from insects, microorganisms, humans, animals and plants, which are reported in databases including that of The Wellcome Trust Sanger Institute (http://miRNA.sanger.ac.uk/sequences/). These miRNAs are about 22 nucleotides in length and arise from longer precursors, which are transcribed from non-protein-encoding genes. The precursors form structures that fold back on themselves in self-complementary regions. Relatively little is known about the functional role of miRNAs and even less on their targets. It is believed that miRNA molecules interrupt or suppress gene translation through precise or imprecise base-pairing with their targets (US Published Patent Application No. 2004/0175732). Bioinformatics analyses suggest that any given miRNA may bind to and alter the expression of up to several hundred different genes; and a single gene may be regulated by several miRNAs. The complicated interactive regulatory networks among miRNAs and target genes have been noted to make it difficult to accurately predict which genes will actually be misregulated in response to a given miRNA. Expression levels of certain miRNAs have been associated with various cancers (Esquela-Kerscher and Slack, 2006 Nat. Rev. Cancer, 6(4):259-269; McManus 2003 Seminars in Cancer Biology, 13:253-258; Karube Y et al 2005 Cancer Sci, 96(2):111-5; Yanaihara N. et al 2006 Cancer Cell, 9(3):189-98).
There remains a need in the art for new and effective tools to facilitate early diagnoses of various lung cancers, as well as less invasive diagnostic tests that could more accurately diagnose malignant disease in patients from other non-malignant diseases and would reduce unnecessary diagnostic surgery, biopsies, PET scans, and/or repeated CT scans.