Under healthy conditions, our cells grow and multiply in a controlled manner. Sometimes a mutation (a change to the DNA that provides instructions on how our cells should behave) or other harmful damage to the DNA can randomly occur when cells divide.  These changes can cause cells to grow and multiply out of control, eventually forming a cluster of abnormal cancer cells known as a tumour.  When this process starts in the lung, it may lead to the development of lung cancer.
Although, in the past, lung cancer has been a disease with typically poor prognosis, newer medicines are being studied to improve the chances of lung cancer patients living longer. Early testing of tumours for particular DNA changes also improves outcomes, as this sometimes allows doctors to select medications that specifically target the tumour.
There is more than one type of lung cancer. The type you have can be identified by looking at a sample of cells from the tumour under a microscope. The type of cancer will determine which treatment options are available to you.  The different types of lung cancer can be divided into 2 main groups.
Small-cell lung cancer (or SCLC) is a very fast-growing type of lung cancer and is typically caused by smoking. Around 1 out of every 10 lung cancers diagnosed are SCLC. 
Non-small cell lung cancer (or NSCLC) is the most common type of lung cancer. Around 9 out of every 10 lung cancers are diagnosed as NSCLC.  There are three main types of NSCLC, with differences seen by looking at a sample of cells under a microscope: 
Your doctor may test a sample of cancer cells taken from the tumour (a biopsy). The type of treatment you receive for your lung cancer will depend on the type, stage and whether the cancer cells produce high amounts of certain proteins.  Different types of lung cancer can be treated using different types of drugs and approaches, so the more your healthcare team know about your type of lung cancer, the easier it is for them to select the right treatment for you. The main treatments for lung cancer are listed below, the choice of which depends on how advanced your lung cancer is. [3, 4]
Surgery – removal of cancer tissue, this may be followed by chemotherapy to destroy any remaining cancer cells.
Neo/adjuvant therapy – neoadjuvant therapy is given before surgery to shrink a tumour. Adjuvant treatment is often given after surgery to kill any remaining cancer cells and lower the risk that the cancer will come back. Neo/adjuvant treatment may include chemotherapy, radiotherapy or biological therapy.
Chemotherapy – these are drugs that stop cancer growing, either by killing the cancer cells or by stopping them from dividing. In some cases, chemotherapy is combined with radiotherapy (known as chemoradiotherapy).
Radiotherapy – the body is exposed to radiation to damage cancer cells and ultimately kill them. This may be used as the only treatment for your tumour, or before/after surgery or chemotherapy to remove any remaining cancer cells.
Anti-angiogenesis therapy – angiogenesis means the growth of blood vessels. Tumour angiogenesis is the growth of new blood vessels that a cancer needs in order to survive. Some cancer cells make a protein called vascular endothelial growth factor (or VEGF). The VEGF protein attaches to cells in blood vessels in the tumour. This triggers the blood vessels to grow so that the cancer can grow. Anti-angiogenesis therapy aims to stop tumours from growing new blood vessels. This might slow the growth of a cancer or sometimes shrink the tumour.
Targeted therapy – ‘targeted therapy’ is a type of treatment that uses drugs or other substances to identify and attack specific types of cancer cells with less harm to normal cells. Examples of types of lung cancer that can be treated with a targeted therapy are:
EGFR-positive NSCLC – during diagnosis, your doctor may order a test to find out whether your lung cancer is positive for an EGFR gene mutation (change); this is also known as EGFR+ NSCLC. Around 1 out of every 7 patients with NSCLC will have EGFR-positive NSCLC.  EGFR (or epidermal growth factor receptor) is a protein that is found on the surface of cells, including in the lungs. EGFR helps the cells grow and divide normally.  When the EGFR gene is mutated it is constantly activated and sends increased survival signals meaning that cells can grow too quickly. 
ALK-positive NSCLC – your doctor may also order a test to find out whether your lung cancer is ALK-positive or ALK+.  Around 1 out of every 20 patients with NSCLC will have ALK-positive NSCLC. [7, 8] ALK (or anaplastic lymphoma kinase) is a protein that is not normally present in healthy lung cells. In ALK+ NSCLC, the ALK gene is mutated (changed) and these changes result in the production of the ALK protein, which increases the growth of cancer cells. Knowing that a tumour is ALK-positive helps doctors plan cancer treatment by using medicines that specifically target ALK. [7, 8]
It is rare for tumours to be both EGFR and ALK positive. 
Cancer immunotherapy – this helps the body’s own immune system to fight cancer and can be used as an alternative to chemotherapy. It is also used in combination with, or after, chemotherapy. While immune cells are able to find and kill abnormal cells, cancer cells are able to protect themselves from immune attack. Cancer immunotherapy aims to beat this protection so that immune cells can find and destroy cancer cells.  Some types of cancer immunotherapy used in NSCLC work by targeting proteins called PD-L1 and PD-1. [11, 12] PD-L1 (programmed death ligand 1) is a protein that interferes with the body’s immune responses and can stop the immune system from fighting cancer. Cancer immunotherapies can be used to block PD-L1 activity, allowing the body’s immune system to destroy the cancer cells. [10, 12]
Your doctor will be able to advise what treatment options are available to you, based on your individual type of lung cancer. It is important to remember that some of these lung cancer drugs only work on tumours that have a particular genetic mutation (EGFR+ or ALK+ NSCLC), so some of the therapies that you hear about might not be suitable for you.
Many targeted therapies and cancer immunotherapies are at the cutting edge of research and may still be undergoing testing. This may mean that the drugs are currently only available in clinical trials. If your specific type of lung cancer does not match what a specific clinical trial is looking at, you will not be able to take part in the clinical trial. Your doctor will be able to advise about the best treatment approach for you, whether it be with a treatment that is already approved to treat your type of lung cancer or in a clinical trial of a new therapy.