Lung cancer refers to the uncontrolled growth of abnormal cells in the tissue of one or both lungs, which takes the form of a malignant tumour.¹¹  The cancer can be found in the airway tubes (bronchus) or in the spongy lung tissue (alveoli). Lung tumours may also be caused by cancer which has spread from another part of the body but these are not considered as lung cancer per se.

There are two main sub-classifications of primary lung cancer:

• Non-small cell lung cancer (NSCLC) – this is the most common form of lung cancer, making up approximately 85% of all lung cancer cases. NSCLC can be classified into a number of types, including:¹
  • Adenocarcinoma – typically found on the outer area of the lungs, in cells that produce mucus
  • Squamous cell carcinoma – typically found in the airways of the lungs
  • Large cell undifferentiated carcinoma – this type of cancer can not be classified as either adenocarcinoma or squamous cell carcinoma.
• Small cell lung cancer (SCLC) – this type of lung cancer tends to spread faster than NSCLC, however it is less common than NSCLC, accounting for approximately 15% of all lung cancers.¹

For most lung cancer cases, genetic mutations are somatic (meaning they happen in cells only specific to that individual and are not inherited).⁴

In rare cases, genetics may play a role in the development of lung cancer, particularly for people who have inherited gene mutations on chromosome 6 (which accounts for approximately 6% of all DNA in cells).^2,3

However the most common cause of lung cancer is cigarette smoking. ¹

The stages of lung cancer are classified by the TNM system which stands for: ⁷

• Tumour (T) – describes the size of the tumour and the extent the cancer has spread into the tissue of the lung. The tumour can be graded from T1a (which describes a tumour under 1cm) to T4 (which describes a tumour larger than 7cm).
• Nodes (N) – describes whether the tumour has spread to nearby lymph nodes. Nodes can be graded from N0, where there has been no spread, through to N3, where the cancer has spread to other areas of the body, such as the other side of the chest or collarbone.
• Metastasis (M) – describes whether the cancer has spread to other areas of the body outside of the lung. Metastasis can be graded from M0, where there has been no spread through to M1c, where the cancer has spread to other organs of the body and produced additional tumours.