Overview

In lung cancer, atypical cells grow in an unmanageable way in the lungs. The cancer cells very likely form a mass-like structure called a tumour. The tumour can grow, spread, and destroy healthy body tissues. When cancerous cells spread from one part to another, it's called the metastatic stage. It is a major health condition that may result in extreme damage to the body.

It is important to understand its causes early to avoid serious health effects. Treatment of lung cancer depends on the person’s medical history and the stage of the disease. It is often diagnosed at advanced stages when treatment options are limited hence it is important to know the causes of it at the earliest.

Primary causes of lung cancer

• Smoking tobacco - Cigarette smoking is the main cause of lung cancer. When anyone inhales cigarette smoke, cancer-causing agents present in the cigarette cause changes in the lung tissue. Tobacco smoke causes exposure to carcinogens (chemicals that cause cancer) such as benzopyrene, chloroethylene, N-nitrosamine, polycyclic aromatic hydrocarbons, aldehydes, and nickel
• Herbal cigarettes, hookah, pipes, cigars, and low-nicotine cigarettes also cause lung cancer
• Smoking can be the main reason for lung cancer in both people who smoke and who are exposed to secondhand smoke also called passive smokers
• Frequent exposure to other people’s tobacco smoke which is called passive smoking can also increase the risk of developing lung cancer

Environmental and occupational factors

• Air pollution - Pollutants from vehicle emissions, industrial processes, household combustion
• Chronic exposure to cooking fumes from burning wood or frying can lead to an increased risk of lung cancer
• Exposure to radon - Radon gas forms from the radioactive decay of uranium, found at differing concentrations in soil and rock. General people are exposed primarily to radon gas entering homes from the soil. Elevated levels of radon are mostly captured in the underground mines where its exposure is at highest
• Asbestos exposure - Asbestos is the name of a group of minerals that occur naturally and are widely used in building materials and industries. Workers in asbestos mines, automotive industry workers, construction workers, painters, and cement plant workers have the highest risk of developing lung cancer. Asbestosis is a lung disease caused by inhaling asbestos fibers
• People who work in industries like rubber manufacturing, coal gasification, coke production, roofing, and paving have the highest risk for lung cancer
• Occupational exposure to cadmium, arsenic, beryllium, mustard gas, silica dust, diesel engine exhaust, etc increases the risk of lung cancer. Silicosis is a lung disease caused by inhaling tiny bits of silica and mainly affects construction and mining workers

Genetic and biological factors

• KRAS (Kirsten rat sarcoma viral oncogene) - These types of gene mutations are mostly found in smokers and can lead to lung cancer progression
• EGFR (Epidermal growth factor receptor) - Commonly found in non-smokers and can cause uncontrolled cell growth and cell division
• A family history of lung cancer can indicate inherited genetic variants which increase susceptibility
• People with compromised immunity, and weakened immune systems may contribute to lung cancer
• People with metabolic disorders like diabetes or obese people have been linked to an increased risk of lung cancer

Pre-existing health conditions

• Asthma - It is a condition in which the airway becomes narrow and swell and it may produce extra mucus which may result in difficulty in breathing occasionally. People with severe or chronic asthma may have a slightly increased risk of lung cancer
• Chronic obstructive pulmonary disease (COPD) - It is a group of lung conditions that may cause difficulty in breathing. The main symptoms of COPD are chronic inflammation of the airways called Bronchitis and damage to the air sacs in the lungs called Emphysema. This damage to the lung tissues may create a favorable environment for the development of cancerous cells
• Pulmonary fibrosis - Scarring of the lung tissue is called pulmonary fibrosis. Scarred or damaged tissues might be at higher risk for lung cancer
• History of pneumonia and tuberculosis - Scarring of lung tissues, and chronic inflammation might increase the risk of lung cancer
• Interstitial lung diseases, asbestosis, and bronchiectasis might elevate the risk of lung cancer
• Smoking with any of these diseases doubles the risk of lung cancer

Infectious agents

• Human papillomavirus (HPV) - It is a viral infection that commonly causes warts on the skin. Some types of HPV infection can cause upper respiratory tract cancer and it is primarily due to habits such as tobacco, poor diet, and more likely to be exposed to toxic substances at work
• Cytomegalovirus - Cytomegalovirus pneumonia can be a life-threatening disease in immunocompromised patients. It may cause sore throat, swollen glands, and chronic inflammation and might play a role in the development of lung cancer cells
• Epstein-Barr virus (EBV) - It has been linked to the development of nasopharyngeal cancer and lymphoma
• Influenza virus - Exposure to influenza increases the risk of lung cancer at a double rate in patients with repeated episodes
• Measles virus - Measles can commonly cause an infection in the lungs like pneumonia, measles may lead to swelling and irritation of the airways, bronchitis, and may lead to cancer forming cells
• Severe acute respiratory syndrome coronavirus 2 - It may cause permanent damage to the lung tissues
• These viruses might contribute to immunity suppression, and genetic alterations and therefore be involved in the development of cancer cells

Emerging and controversial causes

• Vaping or E-cigarette - Vape pens or vaporizers are battery-operated devices that heat a liquid solution usually containing nicotine but not always that turns it into a vapour that can be inhaled. E-cigarettes still are considered an option to help someone who wants to quit smoking and become a nonsmoker but the flavours and stabilisers in this may cause unknown inflammation to the lung tissues. It may cause dry cough or wheezing too
• Antioxidant and vitamin intake -If retinol levels in the diet exceed a certain limit it may contribute to the development of lung cancer, Absorption, transport, distribution, and metabolism of carotenoids and micronutrients might be interfered with by excessive amounts of dietary retinol, which multiplies the possibility of lung cancer
• Excessive consumption of red and processed meat may be associated with the risk of lung cancer but it is completely avoided if consumed in a balanced proportion

Risk factors

• The risk of lung cancer for people who smoke is always higher than for people who don't smoke. The longer anyone smokes and the quantity per day anyone takes increases the risk of lung cancer
• Breathing in the smoke of others also called Passive smoking or secondhand smoke may increase the chance of getting lung cancer
• Constant exposure to radon, especially people staying in the basement, is always a high risk for getting lung cancer
• People who work in mines, textile plants, mills, and places where insulation is used, shipyards are several times more likely to get lung cancer because they come in contact with asbestos. These people might get cancer of the pleura which is the surrounding lining of the lungs called Mesothelioma
• Exposure to uranium, arsenic, beryllium, silica, nickel and chromium compounds, coal products, mustard gas, diesel exhaust
• Based on multiple studies concluded that people who smoked and also took carotene supplements certainly had a higher risk of getting lung cancer
• People who had previous radiation therapy to the lungs particularly if they smoke are at higher risk for getting lung cancer
• Personal or family history of lung cancer may have a higher risk of developing lung cancer

Prevention strategies

• Smoking cigarettes is the main cause of lung cancer that's why smoking avoidance results in decreased chances of lung cancer
• Preventing exposure to secondhand smoke
• Long-term sustained smoking cessation
• Eliminating or reducing exposure to radon, especially in houses, taking steps to prevent radon from entering houses by sealing the basement would result in decreased incidence of lung cancer 
• Eating a lowfat, high-fiber diet, consuming fresh fruits, vegetables, and lots of wholegrains is a balanced diet may lower the chances of lung cancer
• The possibility of getting lung cancer might be reduced by doing consistent exercise and breathing yoga techniques. Symptoms like fatigue, anxiety, and shortness of breath ( dyspnea) might be lowered by doing regular exercise

FAQs

How does smoking cause lung cancer?

Smoking causes lung cancer by damaging the cells that line the lungs. Cigarette smoke is full of cancer-causing substances called carcinogens and these carcinogens cause changes in the lung tissues, firstly body may be able to repair this damage but with constant exposure to carcinogens lungs become more damaged and eventually damaged cells may develop cancer.

What causes lung cancer in non-smokers?

Secondhand smoke, old age, cooking fumes, radon, genetic mutations, family history of cancer, underlying lung disease, oncogenic viruses, occupational exposures, environmental exposures, and air pollutants are the causes of lung cancer in non-smokers.

Does diet and nutrition affect lung cancer risk?

Consuming a healthy and balanced diet may lower the risk of lung cancer.

How can people protect themselves from lung cancer?

People can protect themselves from lung cancer by quitting smoking, lower exposure to environmental pollutants, lower exposure to radon, regular exercise, balanced diet, and lower exposure to occupational hazards.

Summary

Lung cancer also called bronchogenic carcinoma indicates tumours arising in the lung parenchyma or within the bronchi. Smoking is the main cause of lung cancer. Exposure to silica, arsenic, chromium, asbestos, radon, nickel, etc, air pollutants, genetic mutations, family history of cancer, viral and bacterial diseases, weak immune system, previous history of cancer, workers who are closely in contact with carcinogenic substances increases the risk of lung cancer. By taking appropriate precautions, by quitting smoking and acquiring a balanced diet, anyone can stop the spread of lung cancer at a much earlier stage.