Around 3000 Australians will be diagnosed with thyroid cancer in 2018. Overall it has a very good prognosis, with about 96% of people surviving past five years. However, not all thyroid cancers are the same. There are four main types of thyroid cancer and knowing exactly what sort of cancer a patient has is important in developing a treatment plan and giving a patient a good understanding of their unique situation. These four types get their names from the types of cells they develop from and what the cancer cells look like under a microscope.Papillary thyroid cancerThis is the most common type of thyroid cancer. Around 4 in 5 people diagnosed with thyroid cancer will ultimately be diagnosed with papillary thyroid cancer. It usually develops from the follicular cells, which are also known as thyrocytes. These cells produce and secrete thyroid hormones and are found in the lobes or wing-like part of the thyroid. In papillary cancer they start growing faster, forming finger-like projections within a tumour. Papillary thyroid cancer has an excellent prognosis as the tumours are usually very slow growing, though rarely they can spread to lymph nodes. They’re generally treated with surgery, radiation therapy and sometimes chemotherapy.Follicular thyroid cancerAbout 15% of patients have follicular thyroid cancer. This too develops from the follicular cells, however, it doesn’t create the finger-like projections found in papillary thyroid cancer. Follicular thyroid cancer is also very slow growing with an excellent prognosis. It will usually respond well to surgery and radiation therapy but rarely spreads to other parts of the body. In this case, chemotherapy will also be used in treatment.Medullary thyroid cancerThis cancer develops from cells called parafollicular or C-cells, which are large cells that produce a hormone to control calcium levels in your blood. Only about 4% of thyroid cancers are found to be medullary thyroid cancer, so it is much less common than the first two types. It does grow faster and can be more aggressive, spreading to lymph nodes and other organs in the body. It is treated with surgery and chemotherapy.Anaplastic thyroid cancerThis type of cancer is very uncommon, accounting for about 1% of tumours. Anaplastic tumours contain cells that have changed drastically so that they no longer resemble thyroid cells. It grows quickly and can spread early on. Treatment is aggressive to try and control it as quickly as possible, so usually involves surgery, radiation and chemotherapy.There are other types of thyroid cancer, but these are much rarer.