Introduction:
Lung cancer has become very prevalent worldwide, with a risk of 17.2 % in males and 11.6 % in females who are smokers compared to only 1.3 % and 1.4 %, respectively, for non-smokers. Surveys show that by 2030, the number of lung cancer deaths is anticipated to rise to ten million per year. Cigarette smoking is the common causative factor for several chronic respiratory diseases like chronic bronchitis, chronic obstructive pulmonary disease, asthma, and lung cancer. Thus often in many smokers, both lung cancer and chronic airway disease co-exist. Several clinical studies have shown an association of this kind. The major chronic respiratory diseases are chronic obstructive pulmonary syndrome, asthma, respiratory allergies (allergen that triggers the airway and causes inflammation), sleep apnea (pause in breathing during sleep), occupational lung disorders, cystic fibrosis (a disorder where the mucous become thick and sticky), and pulmonary hypertension.
Apart from genetic and infectious traits, the major risk factors for chronic airway disease include long-term exposure to tobacco primary and secondary, outdoor and indoor air pollutants, occupational agents, allergens, nutrition, diet, and socioeconomic factors. In this article, we will discuss the link between some of the common chronic airway diseases and lung cancer.
What Are the Common Chronic Airway diseases?
Chronic respiratory diseases are the chronic disease of the respiratory pathway and other structures of the lungs. Every year one billion people are affected by some chronic respiratory illness which accounts for 4.2 million deaths worldwide. Some of the common chronic airway diseases are as follows:
-
Chronic Obstructive Pulmonary Disease (COPD): It is a chronic lung disease that includes chronic bronchitis (chronic inflammation of the bronchi) and emphysema (damaged air sacs and lungs cause shortness of breath), and patients suffer from difficulty breathing. It causes inflammation of the airways and obstructs normal airflow. It occurs due to long-term exposure to cigarette smoke, particulate matter, or gasses. Patients with COPD (chronic obstructive pulmonary disease) risk developing lung cancer, heart disease, and various other conditions.
-
Asthma and Respiratory Allergies: Asthma is characterized by chronic airway inflammation, reversible airway obstruction, and increased bronchial reactivity. Common symptoms are wheezing, chest tightness, breathlessness, cough, and sputum. Respiratory allergy is a hypersensitive response of the respiratory tissues in response to sensitization of the immune mechanism by allergens. Asthma and respiratory allergy show similar symptoms and have common triggering factors.
-
Occupational Lung Diseases: Lung conditions that are caused by or sometimes worsened by long-term exposure to irritants at the workplace. Chemicals, fungal spores, dust particles, and animal droppings are common irritants that increase the risk of developing occupational lung diseases.
-
Sleep Apnea Syndrome: A sleep disorder wherein breathing is stopped repeatedly, breaking the continuity of sleep.
-
Pulmonary Hypertension: High blood pressure affects the arteries of the lungs and heart.
What Are the Causes of Lung Cancer?
When some cells of the lungs undergo certain abnormal changes and multiply uncontrollably, a tumor forms resulting in lung cancer; in the early stages, it is not presented with significant signs and symptoms; however, in the later stages, people may show frequent coughing, blood in the mucous, chest pain, breathing problems, and difficulty in speaking and swallowing.
Based on the size of the cells affected, lung cancer can be divided into small cells (the cancer cells are smaller and are fast-growing) and non-small cells (the cancer cells are larger and behave similarly to squamous cell carcinoma) cancers. 80 to 5 percent of the reported lung cancer cases are non-small cell, and small cell cancer accounts for only 15 percent.
One of the major causative factors for lung cancer is cigarette smoking. It is also caused by using other sources of tobacco such as cigars and pipes, inhaling secondhand smoke, exposure to radon or asbestos at sites of occupation, and a family history of lung cancer. Several clinical studies reveal that people with chronic airway diseases are at higher risk of developing lung cancer at an earlier or later stage.
What Is the Link Between Chronic Airway Diseases and Lung Cancer?
Lung cancer and chronic respiratory diseases are usually referred to as “complex diseases.” This section will show the relationship between some of the most commonly seen chronic airway diseases and lung cancer.
1. Chronic Obstructive Pulmonary Disease (COPD) and Lung Cancer: Cigarette smoking is the main contributing factor to developing chronic obstructive pulmonary disease and lung cancer. Several clinical studies have revealed that there are several other factors linking these two diseases beyond a common etiology. Smokers with obstructive airways are five times more likely to develop lung cancer than those with a normal airway, and COPD is an independent risk factor for lung cancers. This relation suggests that some common mechanism, like premature cellular aging or the presence of certain growth factors, is present in the pathogenesis of both conditions. Some of the common factors are as follows:
- Genetic Predisposition to Chronic Obstructive Pulmonary Disease and Lung Cancer: Lung cancer and COPD has familial susceptibility, and the underlying genetic predisposition is the same for both diseases. Some genetic changes are responsible for inflammation-causing COPD tumor growth responsible for cancer.
- Epigenetic Changes: In addition to genetic changes, epigenetic (changes in gene activity without changing the DNA sequence) modifications like deoxyribonucleic acid methylation (addition of methyl groups to the DNA), covalent histone modifications(process altering the chromatin structure), microRNAs expression (controls gene expression), etc., play an important role in the progress of lung cancer and COPD.
- Oxidative Stress: The free radicals produced in cigarette puffs are reactive oxygen and nitrogen species. They create oxidative stress in the cells. It is responsible for the DNA (deoxyribonucleic acid) damage in cancer cells and inflammatory processes in chronic obstructive pulmonary disease.
2. Asthma and Lung Cancer: Studies reveal an increased risk of developing lung cancer in chronic asthmatic patients. Tobacco smoking is a predisposing factor for both diseases. However, asthmatic patients without smoking habits also presented an increased risk of developing lung cancer. The inflammatory cells responsible for the pathogenesis of asthma played a pivotal role in the development of lung cancer also.
3. Occupational Lung Diseases and Lung Cancer: Long-term exposure to chemicals from occupational sites may result in chronic respiratory illnesses like allergies and asthma. Some of these chemicals are carcinogenic (potential to cause genetic changes in the cells that predispose to cancer), and long-term exposure may pivot the pathogenesis of cancer.
Conclusion:
As a general rule, it can be assumed that a chronic respiratory illness predisposes to lung cancer; They have a common etiology, and apart from that, several common mechanisms in the pathogenesis of lung cancer and chronic airway disease suggest the link between the two.
