Lung Cancer and Smoking

Introduction

The lungs are vital organs we need to breathe and survive. They allow oxygen to be transferred from the atmosphere into our blood, which is then transported to muscles and other organs. If the lungs become damaged, cancerous growths or tumours may begin to grow. Lung cancer is the third most common cancer and the leading cause of cancer-related death worldwide.¹

The most common causes of lung cancer are environmental factors such as smoking, exposure to ionising radiation, air pollution, and exposure to carcinogens in the workplace. In fact, 3 out of 4 cases of lung cancer in the UK are preventable - so it is extremely important to understand how to reduce your risk of developing this aggressive cancer.² 

Smoking tobacco is the most significant and well-known risk factor for developing lung cancer. Smoking cigarettes, pipes or cigars all significantly increase your cancer risk. Since the 19th century, when the mass production of tobacco products significantly increased, lung cancer has become one of the most common cancers across the world.³

Significantly, over 70% of lung cancers are caused by smoking and its effects on the lungs and body. Whilst it is still possible for non-smokers to develop lung cancer, their risk is substantially reduced.⁴ As such, the medical community is now working to educate the world’s population about the risks of smoking and, where possible, convince smokers to quit.

Lung cancer

Types of lung cancer

There are many types of lung cancer, which are split into 2 main groups:

• Non-Small Cell Lung Cancer (NSCLC)
• Small Cell Lung Cancer (SCLC)

NSCLCs are more common than SCLCs. This group is further divided into 4 types of NSCLC: adenocarcinomas, squamous cell carcinomas, large cell carcinomas, and NSCLC not otherwise specified (NOS) (reserved for when a pathologist cannot determine the exact type of cancer). 

• Adenocarcinoma is often seen in non-smokers. It originates from the lung cells that produce mucus, which are found in the outermost parts of the lungs
• Squamous cell carcinoma develops from cells that line the airways. Both squamous cell carcinoma and large cell carcinoma are found in the centre of the lung(s)⁵ 

SCLC is less common than NSCLC, but still makes up around 15% of lung cancer cases. It is often fast-growing and aggressive and has been frequently associated with smoking.⁶ 

Symptoms and early detection

All lung cancers (regardless of their type and origins) are associated with similar symptoms. Some of these symptoms include:⁷

• A persistent cough 
• Recurrent chest infections (or persistent infection)
• Breathlessness or feeling wheezy for no apparent reason
• Coughing up blood 
• Pain in the shoulder or chest regions
• A hoarse voice that does not improve 
• Fatigue and loss of appetite
• Unexplained weight loss

Experiencing these symptoms does not definitively mean that you have lung cancer, but you should consult a healthcare professional. 

If a GP is concerned about lung cancer, they will perform further tests to investigate. This often starts with a general physical examination during which your doctor will listen to your lungs with a stethoscope, measure your lung capacity using a spirometer, and take a blood sample for analysis. 

This examination will be followed by imaging, often starting with a simple chest X-ray to look for masses within the chest. X-rays are good at looking for larger masses, but they are not very good at spotting small masses or distinguishing between cancerous and non-cancerous masses. Consequently, a CT scan is usually performed as well to generate a 3D image of the lungs, which is far more detailed than the pictures from an X-ray. If your doctor is still concerned, a sample of the lung cells or tissue (biopsy) may be taken and sent to a laboratory to identify what the mass is. The technique used to take the biopsy will vary based on the location and size of the mass.⁸

Prognosis

Prognosis and survival depend on many factors, including the stage of cancer at diagnosis, the type of lung cancer, and other comorbidities (multiple illnesses or conditions at once) the patient has. The chances of surviving 5 years or more with stage 1 lung cancer are much greater than with stage 4. Regardless, approximately 20% of patients will survive 5 years or more and only 10% will survive 10 years or more.⁹ This is why it is important to reduce the risk factors associated with lung cancer, such as smoking, as much as possible.

The link between smoking and lung cancer

What is in cigarette smoke?

There are over 5000 harmful chemicals in tobacco cigarettes that can be inhaled while smoking. At least 70 of these are carcinogenic compounds, which dramatically increase your chances of developing cancer. Some of these chemicals can be encountered in other everyday ways, including rubber manufacturing, in batteries, in nuclear reactors and in oil and coal. 

Cigarettes also contain tar, a black substance which accumulates in the lungs, increasing the risk of developing other serious lung conditions such as emphysema and chronic obstructive pulmonary disease (COPD). Although it does not directly cause cancer, nicotine is one of the major factors that result in individuals becoming addicted to smoking. Hence, many smokers struggle to quit smoking due to nicotine dependence, despite the known risks of smoking associated with lung cancer. 

How does smoking cause lung cancer?

DNA damage

DNA carries the genetic material that codes for essential proteins required for an organism’s development and function. In other words, DNA is the instruction manual for our body’s cells. DNA damage occurs all the time, and the body constantly repairs damaged DNA via tightly regulated processes to maintain the fidelity of the DNA code and eliminate cancerous cells before they divide. 

Smoking increases the rate of DNA damage and increases the likelihood that the proteins controlling DNA repair and cancer prevention become damaged themselves. The chemicals within tobacco smoke can also prevent cells from repairing their damaged DNA, further increasing the chances of cancer developing.

Furthermore, tobacco smoke coats the airways of the lungs, preventing oxygen from entering the blood, and preventing the cells lining the airway from working properly. With the hair-like cilia unable to remove the smoke and clear the airway, toxins and bacteria can accumulate in the lungs, causing further lung and cell damage. As such, smoking increases the rate of developing lung infections and persistent coughs.¹⁰ 

Immune system suppression

Research has found that inhaling tobacco smoke has a suppressive effect on the immune system and influences the cells that surround tumours (tumour microenvironment).¹¹ Normally, the immune system is constantly surveying the body and killing cancerous cells. However, when the immune system is suppressed by the toxins inhaled whilst smoking, lung cancer (and 15 other types of cancer) becomes much more likely to develop.¹²

What are the health risks associated with smoking?

In addition to being the primary cause of lung and many other cancers, smoking can also increase your risk of heart disease and other primary lung diseases. Many other bodily functions can be negatively affected by smoking, including your sight, dental health, fertility, and bone health. Smoking also increases the risks of mental health issues such as anxiety and depression. Additionally, individuals who smoke while undergoing cancer treatment do not respond well to treatment and have a higher relapse rate.¹³

Even ‘low level’ smoking increases your risk of lung cancer - but smoking more and for a longer time increases your risk. Small cell and squamous cell lung cancer are linked most closely with smoking. Approximately 86% of lung cancer deaths in the UK are attributed to tobacco smoking, and the chance of dying from lung cancer is 15 times greater in smokers compared to people who have never smoked.¹⁴ 

Quitting smoking 

The most effective way to prevent lung cancer is to never take up smoking. If you do smoke, quitting as soon as possible is your best option. However, quitting smoking is often challenging due to the addictive nicotine found in cigarettes. Many quitting aids are available, and most healthcare providers can provide support. Some of these methods include:¹⁵

• Going cold turkey 
• Nicotine replacement therapy
• Medication to help with withdrawal symptoms
• Lifestyle changes - for example, using cognitive behavioural therapy (CBT) 

Quitting smoking as early as possible offers several health benefits. 1 year after quitting, your risk of heart attack is reduced by half, and 10 years after quitting, your risk of dying from lung cancer will also have reduced by half, compared to an individual who smokes regularly.¹⁴

Summary

There is a clear association between inhaling carcinogenic toxins via tobacco smoking and the development of lung cancer. Smoking causes damage at a cellular level, resulting in the accumulation of DNA damage. Whilst the body would normally be able to repair this damage, the extent and frequency of the damage caused by smoking overloads this system.

Furthermore, smoking exposes the lungs and body to many harmful toxins that further hinder the DNA repair process. Together, this explains smokers’ substantially higher risk of developing lung cancer. The best way to mitigate the impact of smoking on your lung cancer risk is to quit smoking as soon as possible and, ideally, never taking up smoking in the first place. If you would like support to quit smoking, you should seek advice from your healthcare professional. 

The following websites also offer support for those looking to quit smoking:

• NHS - Quit smoking - better health
• Cancer Research UK - How do I stop smoking?
• Asthma and Lung UK - How to quit smoking - the best ways to quit