Relationships between chronic obstructive pulmonary disease and lung cancer: biological insights

Abstract

Lung cancer (LC) has become one of the leading causes of preventable death in the last few decades. Cigarette smoking (CS) stays as the main etiologic factor of LC despite that many other causes such as occupational exposures, air pollution, asbestos, or radiation have also been implicated. Patients with chronic obstructive pulmonary disease (COPD), which also represents a major cause of morbidity and mortality in developed countries, exhibit a significantly greater risk of LC. The study of the underlying biological mechanisms that may predispose patients with chronic respiratory diseases to a higher incidence of LC has also gained much attention in the last few years. The present review has been divided into three major sections in which different aspects have been addressed: (I) relevant etiologic agents of LC; (II) studies confirming the hypothesis that COPD patients are exposed to a greater risk of developing LC; and (III) evidence on the most relevant underlying biological mechanisms that support the links between COPD and LC. Several carcinogenic agents have been described in the last decades but CS remains to be the leading etiologic agent in most geographical regions in which the incidence of LC is very high. Growing evidence has put the line forward the implications of COPD and especially of emphysema in LC development. Hence, COPD represents a major risk factor of LC in patients. Different avenues of research have demonstrated the presence of relevant biological mechanisms that may predispose COPD patients to develop LC. Importantly, the so far identified biological mechanisms offer targets for the design of specific therapeutic strategies that will further the current treatment options for patients with LC. Prospective screening studies, in which patients with COPD should be followed up for several years will help identify biomarkers that may predict the risk of LC among these patients.

Keywords: Chronic obstructive pulmonary disease (COPD); epidemics; etiologic agents; lung cancer (LC); underlying biological mechanisms.

Figure 1

Schematic representation as highlighted by the sign ¶ of the most relevant etiologic factors of lung cancer in patients. Cigarette smoking, occupational exposure (including several procedures and materials), diet, physical activity, radiation, and air pollution are the most relevant etiologic agents of lung cancer.

Figure 2

Schematic representation of the potential role of cytokines in tumor development in patients with underlying COPD. Cigarette smoking induces chronic inflammatory events characterized by the induction of several interleukins (IL), cyclooxygenase-2 activity, and cytokines. These inflammatory molecules interfere with key regulatory mechanisms such as cell death (apoptosis), cell repair, and angiogenesis, which contribute to the neoproliferative including tumor growth and metastasis.

Figure 3

Schematic representation whereby redox imbalance may induce damage in cells. Reactive oxygen species (ROS) are formed by the addition of electrons to the oxygen molecule leading to the formation of different ROS. Oxidative stress takes place in cells and tissues as a result of an imbalance between oxidants and antioxidants in favor of the former. Oxidative damage in tissues is induced through several mechanisms such as peroxidation of membrane lipids, alterations in nuclear DNA, or oxidation of cell proteins.