Lung cancer develops from the abnormal and uncontrolled growth of cells found in the respiratory tract and in lung tissue. This process of abnormal cell development results in a mass of cells known as a tumour. Malignant tumours are characterised by their ability to grow out of control, invading other tissues in the body.
Lung cancer is classified into two major groups, depending on the size and appearance of the malignant cells: non-small cell lung cancer (NSCLC) (accounting for 85% of the cases) or small cell lung cancer. Its tumours are completely different in terms of how they act and their treatment and prognosis.