Biomarkers in Exhaled Breath Condensate and Serum of Chronic Obstructive Pulmonary Disease and Non-Small-Cell Lung Cancer

Chronic obstructive pulmonary disease (COPD) and lung cancer are leading causes of deaths worldwide which are associated with chronic inflammation and oxidative stress. Lung cancer, in particular, has a very high mortality rate due to the characteristically late diagnosis. As such, identification of novel biomarkers which allow for early diagnosis of these diseases could improve outcome and survival rate. Markers of oxidative stress in exhaled breath condensate (EBC) are examples of potential diagnostic markers for both COPD and non-small-cell lung cancer (NSCLC). They may even be useful in monitoring treatment response. In the serum, S100A8, S100A9, and S100A12 of the S100 proteins are proinflammatory markers. They have been indicated in several inflammatory diseases and cancers including secondary metastasis into the lung. It is highly likely that they not only have the potential to be diagnostic biomarkers for NSCLC but also prognostic indicators and therapeutic targets. 1. Introduction Chronic obstructive pulmonary disease (COPD) and lung cancer are the leading causes of deaths worldwide which are associated with cigarette smoking. COPD is a preventable and treatable disease characterised by progressive, irreversible airflow obstruction resulting from chronic airway inflammation [1–3]. It is responsible for 5.8% of all deaths (3.28 million deaths in 2008) and expected to become the third leading cause of death by 2030 [4]. Lung cancer, on the other hand, is defined as cancer which arises from cells of respiratory epithelium [5]. It has been the global leading cause of cancer death (approximately 1.8 million deaths per year) since 1985 [5], accounting for 12.4% of total new cancer cases diagnosed [5] and almost as many deaths as those from prostate, breast, and colon cancer combined [6]. The majority (85%) of lung cancer is non-small-cell lung cancer (NSCLC), and it can be further divided into adenocarcinoma, squamous cell carcinoma, and large cell carcinoma comprising 38.5%, 20%, and 2.9% of all lung cancer cases, respectively [5]. Despite significant advances in 5-year survival rates of other cancers, that of lung cancer remains low at 15.6% (compared to 66% for colon cancer, 94% for melanoma, 90% for breast cancer, and 100% for prostate cancer) [6, 7]. Even more disappointingly, >52% of the patients have distant metastases (stage IV) at the time of diagnosis with a resultant 5-year survival of <3.6% (Figure 1) [5]. This is in stark contrast to the 60%–80% 5-year survival rate for patients with stage I lung cancer [8]. Patients usually present late