LUNG CANCER IN NON SMOKERS

Smoking is one of the leading causes of lung cancer, but many cases of lung cancer are seen in individuals who have never smoked ever in their life!

Around 10-15% of lung cancers arise in non-smokers.

EPIDEMIOLOGICAL FACTORS

1. Age- Lung cancer risk increases with age among both smokers and non-smokers. The typical age of presentation is beyond 40 years.

2. Gender- Lung cancer incidence rates are higher in women than men among non-smokers for the age bracket of 40-70 years.

3. Race/Ethnicity- Lung cancer incidence rates are higher in African-Americans and Asians than whites.

NON-SMOKING CAUSES OF LUNG CANCER

#1 Second-hand smoke- It was back in 1981 when published reports from Japan and Greece indicated increased lung cancer risk in non-smoking women married to smoking men. A causal association has been established between passive smoking and lung cancer due to the presence of carcinogens in side stream smoke.

#2 Radon- It is a respiratory carcinogen and is important not only for the underground miners but for the general population as well. Radon, an inert gas, is produced from the decay of radium. Radon with a half-life of 3.82 days decays into polonium-218 and polonium-214 which emit alpha particles, which are high-energy and high-mass particles that cause DNA mutations and break in the chromosomal structures. An important thing to notice is that the penetration power of the alpha particles is not related to concentration meaning that the radon particle is equally damaging in low and high concentrations. There can be permanent damage to a cell by just one hit from an alpha particle. High chances of lung cancer are present in underground miners due to radon exposure. In a study of 757 miners, 34 deaths were reported from lung cancer against the expected rate of 10, meaning that 3.4 times higher mortality was observed in these groups of miners.

In the 1970’s, there was widespread recognition that radon is present in indoor environments including homes, giving rise to concerns! Studies conducted in both North America and Europe showed a considerably increased risk.

#3 Outdoor Air pollution – Vehicles, Industries, and powerplants are the main culprits. Studies have confirmed an increased risk of lung cancer for increasing levels of air pollution.

#4 Indoor Air Pollution-  About half of the world population, mostly in low resource countries use solid fuels for cooking in poorly ventilated spaces. Product of incomplete combustion contain carcinogens such as benzopyrene, formaldehyde, and benzene exposure to which has been known to cause lung cancer

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2. Coal- Use of coal for cooking and heating was associated with increased lung cancer risk among non-smokers, especially seen in China.

3. Biomass- Studies conducted in Japan, China, and Mexico found an increased risk of lung cancer among non-smoking women exposed to smoke while cooking with various biomass fuels.

4. Cooking fumes- Stir-frying, deep-frying, and pan-frying which involves heating oil to high temperatures is practiced worldwide, especially in China and studies have found a positive correlation between lung cancer in non-smokers and cooking fumes.

#5 Occupational Agents

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2. Asbestos- Studies have proven an increased risk of lung cancer among non-smokers who were exposed to asbestos especially in shipyard and dock workers. The risk of cancer is determined by the level of exposure to asbestos and also the exposure to the type of fibers.

3. Arsenic- Copper smelter workers from Sweden and Chinese tin mines emitting arsenic have shown an increased risk of lung cancer among the workers.

4. Silica- Several industry-based studies of workers exposed to silica have reported an increased risk of lung cancer among non-smokers.

#6 Other risk factors

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2. Arsenic in drinking water especially seen in the case study in Chile has shown a positive correlation with lung cancer

3. Human Papilloma Virus(HPV)- HPV 6, 16, and 18 causing infections have been associated with lung cancer.

4. Human immunodeficiency virus(HIV)- HIV has been associated with an increased risk of lung cancer.

5. Ionizing radiations- Many studies have shown an increased risk of lung cancer due to radiation treatment of Hodgkin’s disease or breast cancer.

#7 Apart from the above-mentioned causative factors for lung cancer some factors are protective for lung cancer and include-

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2. Fish consumption- High fish consumption was found to decrease the risk of lung cancer among non-smokers.

3. Micronutrients-  Consumption of carotenoids, alpha and beta carotene, vitamin A and vitamin C have shown a negative correlation with lung cancer.

4. Hormone replacement therapy- Generally an obsolete form of therapy but when was given earlier showed protective factors from lung cancer.