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Lung Cancer in non-smokers: Exploring causes and risk factors

The term "never smoker" refers to individuals who have smoked fewer than 100 cigarettes in their lifetime or has never smoked. The incidence of lung cancer in never smokers is increasing worldwide, and they are occurring at a younger age and more women are being diagnosed. Lung Cancer in never smokers accounts for approximately 15-25% of the total lung cancer cases, and is a significant public health problem.
The first question asked when a non-smoker is diagnosed with lung cancer is what is the cause and why did it happen to them even though they never smoked. Several causes and risk factors have been postulated to cause lung cancer and it suggests a multifactorial carcinogenic process.

The factors commonly associated are: Outdoor air pollution , second hand smoke, domestic fuel smoke (wood burning), chronic pulmonary diseases, occupational exposure to carcinogenic chemicals ( silica , arsenic, chromium, cadmium, nickel), Ionizing radiation (such as radon), family history and genetic causes.

Second hand smoke — Second hand smoke is an important risk factor for lung cancer among never smokers. An American multicenter study found a 30% increase in the risk of lung cancer in never-smokers with a smoking spouse. Importantly, there is also an increased risk for those non-smokers that have a spouse that is a smoker. In a meta-analysis that included 55 studies, it was found that women who were married to a smoker had a 27% increase in risk of lung cancer.



Air pollution - Outdoor air pollution is a mixture of various pollutants originating from natural and anthropogenic sources, such as transportation, industrial activity, power generation, among others. Outdoor air pollution and particulate matter from outdoor air pollution as carcinogenic to humans
Radon: Radon is a radioactive gas produced from the decay of uranium present in soil and rocks. It was defined as a human carcinogen by the International Agency for Research on Cancer (IARC) in 1988 and epidemiological studies have successfully correlated radon exposure to lung cancer both in miner workers and other environmentally exposed populations. It is considered the second most important risk factor for the development of lung cancer after tobacco and probably the main risk factor amongst never smokers.
Occupational exposure to carcinogenic chemicals or ionizing radiation: Occupational exposure to different kinds of carcinogenic chemicals or ionizing radiation is thought to be associated with 5-10% of lung cancer cases, and asbestos exposure is currently the most important factor, with a 5-fold increased risk of lung cancer.

Family history/genetic causes: More recently, studies have also investigated the possibility of inherited predisposition to lung cancer, and it is estimated that 5-10% of lung cancer patients present germline mutations in hereditary cancer genes. Familial aggregation studies have estimated an increased risk of developing lung cancer of up to 4-fold according to family history of lung cancer in first degree relatives and respective age at diagnosis

Lung Disease: Another important risk factor for the development of lung cancer in non-smokers is underlying lung disease.



Environmental Exposures: Several studies have also linked environmental exposures to lung cancer — some known exposures including asbestos, chromium, and arsenic. Chronic exposure to cooking fumes from burning wood or frying has been linked to an increased rate of lung cancer in non-smokers. This problem is most evident in developing countries where women are primarily in charge of cooking duties and can spend hours each day cooking amongst open flames. This exposure is thought to be the cause of some of the disproportionate lung cancer rates within this population.

There is no screening test recommended for lung cancer in non-smoking men and women. The symptoms of lung cancer should not be overlooked in women and non-smokers. The treatment of lung cancer in non-smokers is similar to smokers but the prognosis is better. Most of them harbour mutations which are treated with newer targeted agents and therapies. Regardless of smoking status, women with lung cancer tend to outlive men with lung cancer.

(Dr. G. Vamshi Krishna Reddy , Director-Oncology Services, Consultant Medical Oncologist & Hemato Oncologist , Yashoda Hospitals, Hyderabad)


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