Understanding Lung Cancer – What it is, how it happens, types

What is lung cancer?
It is the cancer that develops in the tissues of lung, mostly in the cells that line the airways. More often than not, a lung tumour originates in the walls of the large, branching airways of the lung, the bronchi. More than 20 different tumours can develop in the lung itself.

Cancer that forms in the lungs is broadly divided into two types – small cell and non-small cell lung cancers, based on the way the cancerous cells appear under a microscope. A cancer can be a mixed one too, with cells of both types present at one time.

Non-small cell cancer of the lung – This is the most common type of cancer afflicting the lung, originating in the cells inside lung airways, commonly in the centre of lungs. Smoking increases the risk of this cancer type. It can be of the following types:

• Squamous cell carcinoma – It is usually found in the centre of bronchi and easiest to detect because it shows up in mucous samples. It spreads slowly and can be treated if detected early.
• Adenocarcinoma – This is generally found in the outer part of the lung, common among smokers and even non-smokers.
• Large-cell carcinoma – These are large, abnormal cells that develop on the lung’s outer edges. This tumour has a high tendency to spread.

Small-cell cancer of the lung – This cancer usually develops in the central bronchi and is the most aggressive form of cancer found in lung. It has usually spread (metastasized) to lymph nodes and distant organs by the time the person gets diagnosed.

What causes cancer in the lung?
A lung tumour or cancer may result from the following:
• Smoking – Tobacco contains over 4000 different chemicals, of which many are known to have carcinogenic properties. Smoking is the biggest cause for cancer in the lung, along with family genetics. A person who smokes one pack of cigarettes daily is about 20 times more likely to develop cancer than a non-smoker. The risk triples in a person who smokes two packs a day.
• Passive smoking – Inhaling tobacco smoke from others or spending a lot of time in smoky areas increases the risk of a person towards this form of cancer. According to WebMD.com, people who share a home with a smoker are at a 30 per cent higher risk of developing this cancer than those who stay in a smoke-free home.
• Exposure to chemicals – People working in certain jobs and industries get exposed to chemicals that harm the lungs. Some common chemicals include asbestos, radon, cadmium, polycyclic aromatic hydrocarbons (PAHs), etc.
• Air pollution – Breathing in polluted air from industrial plants and vehicles over a long period of time expose a person to cancer. The risk is quite similar to that of passive smoking.
• Lung diseases – A lung tumour can grow easily in a lung that has been scarred from a previous infection or disease like tuberculosis, chronic obstructive pulmonary disease (COPD) or scleroderma.
• Genes – Science has discovered a gene on chromosome 6 that can increase the risk of cancerous growth in the lungs. Further, some families seem to be more prone to the cancer than others.

What happens once cancer originates?
The cancer is said to originate once cells begin to grow uncontrollably in one or both lungs. These cells stop carrying out their usual functions and divide to create more abnormal cells, rather than healthy lung tissue. The resulting tumour begins to interfere with the lung’s functioning, i.e. transfer oxygen to the blood to reach every cell in the body. The person begins to experience respiratory discomfort of varying degree, following which s/he must be diagnosed to commence lung cancer treatment at the earliest.