Abstract
BACKGROUND: The relationship between inflammation, air obstruction and lung cancer is complex and there is still great uncertainty regarding their underlying pathophysiology. Our aim was to investigate the inflammation pathways that are implicated in both chronic obstructive pulmonary disease (COPD) and lung cancer. METHODS: A literature search was performed in PubMed to identify relative studies published until June 2011. RESULTS: The pathophysiology of both COPD and lung cancer includes dysregulation of the inflammation process, but the cascade of signaling events is not yet fully understood. Both lung cancer and COPD are associated with cigarette smoking that induces a chronic inflammatory state in the lung by generating reactive oxidant species. It is considered that shared inflammatory pathways involve genetic and epigenetic changes due to chronic tissue injury and abnormal tumor immunity in susceptible hosts. The proposed role of chronic inflammation is based on the 2-stage model of carcinogenesis. According to this model, genotoxic injury is crucial in tumorigenesis, followed by promotional events that result in clonal growth of modulated cells. Research has shown that chronic inflammation creates the necessary environment for the development of lung cancer, acting as a tumor promoter. This environment, in combination with cigarette smoke, induces the upregulation of mediators of the inflammatory response, such as cyclooxygenase-2. This leads to the production of inflammatory cytokines through lymphocytes, such as IL-1, IL-6, IL-8 and IL-10, as well as to the increased formation of chemotactic factors. Some of the latter mediators may suppress cell mediated immune response and promote angiogenesis. They also impact cell growth, resulting in the inhibition of apoptosis. Inflammatory factors promote oxidative stress, contribute to the generation of reactive oxygen, and cause oxidative DNA base modification. COX-2 also plays an important role in promoting epithelial-to-mesenchymal transition, present in both lung cancer and COPD. Thus, chronic inflammation plays a pathogenic role in lung cancer by inducing preneoplastic mutations and cellular damage. CONCLUSIONS: Additional research is required to understand the cellular and molecular mechanisms that link COPD and lung cancer, in an effort to discover new methods of prevention and treatment.