This is the first part of our series about the condition based on our patient booklet “Fast Facts for Patients: Non-small Cell Lung Cancer with KRAS Mutation”. This article explains what non-small cell lung cancer (NSCLC) is and how lung cancer can develop.

First, the Facts

  1. Non-small cell lung cancer (NSCLC) is one of two main types of lung cancer.
  2. Some lung cancers spread to other parts of the body before they are diagnosed. A cancer that has spread is called ‘metastatic’.
  3. New lung cancer treatments are being developed that directly target the gene mutations that control how cancers grow and spread.
  4. The most important gene mutations in cancer are called ‘driver mutations’. In NSCLC, this includes KRAS mutations, which can be used as targets for treatment.
  5. There are new treatments designed for lung cancers with a KRAS mutation that are already available. And more are being developed.
  6. Treatments in development are tested in clinical trials. There are several different phases of clinical trials that people with cancer can take part in.

What Is Non-Small Cell Lung Cancer?

Non-small cell lung cancer – abbreviated to NSCLC – is one of the two main types of lung cancer; 85% of lung cancers are NSCLC, the other 15% are called small cell lung cancers.

There are three main types of NSCLC that develop from different types of lung cells.

Three main types of NSCLC: adenocarcinoma, squamous cell carcinoma, large cell carcinoma

Adenocarcinoma develops from gland cells in the lungs, which produce mucus. The mucus helps to trap any irritants that get into your airways so you can get rid of them by coughing. Around 4 in 10 lung cancers (40%) are this type.

Squamous cell carcinoma develops from flat cells that line the inside of the airways of the lungs. Around 3 in 10 lung cancers (30%) are this type.

Large cell carcinoma usually develops in the outer area of the lungs. It’s called that because the cancer cells look particularly large under a microscope. These cancers are sometimes called ‘undifferentiated’. That means the cells are not specialized as normal lung cells are. About 1 in 10 lung cancers (10%) are this type.

There are other subtypes of NSCLC that are much rarer. Together, they make up about 1 in 20 cases (5%).

Subtypes of non-small cell lung cancer

How Can Lung Cancer Develop?

We can’t tell exactly what causes each case of lung cancer. But there are risk factors we do know about.

Tobacco smoke is the main risk factor for lung cancer, causing about 8 out of 10 cases (80%).

Some people get lung cancer because of substances they’ve been exposed to. Asbestos – a fibre used for insulation – is a severe lung irritant that can cause cancer many years later. It’s now banned in many countries, but people working in the building industry may come into contact with it. Silica and diesel exhaust fumes are other workplace risk factors.

Air pollution can cause lung cancer. The risk varies, depending on the levels of pollution where you live and work.

There is radiation that occurs naturally in rocks, water, and air, as well as cosmic radiation that comes from space. Radon gas is produced by the natural decay of uranium. Levels are higher in some areas than others and can increase the risk of lung cancer, particularly for people with a history of smoking.

Risk factors for lung cancer: tobacco smoke, exposure to substances, air pollution, radiation

Why Do Some People Get Cancer and Not Others?

Everyone is at risk of developing lung cancer, irrespective of their smoking history. However, smoking can interact with other factors and increase your risk. Some people are more prone to cancer than others, particularly if there are other cases in their close family.

Some cancers occur randomly, and we never know the cause. And some may be due to risk factors we don’t know about yet.


Information based on Fast Facts for Patients: Non-small Cell Lung Cancer with KRAS Mutation (Karger, 2023).

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