Cancer is a disease that is caused when cells in the body divide in an uncontrollable manner. This result in production/growth of accumulated mass of cells or lump which are called tumours. The branch of biology dealing with prevention, diagnosis and treatment of cancer or tumours is called cancer biology. Till now, more than 200 types of cancer have been discovered. Cancer is classified based on the origin of tumour cells. There are various biochemical, genetic and environmental factors that contribute in development of cancer. It can be caused by genetic defects that are passed on generation to generation. Most cancer cases occur due to genetic mutations resulting from irregular lifestyle, obesity and other environmental factors. Some viruses are also causative agents of cancer such as Herpes virus and Human Papillomavirus. Some autoimmune diseases are also linked with cancer such as Crohn disease and celiac disease. Cancerous cells are of two types-benign and malignant. Benign tumour cells do not spread to other parts of the body. Malignant tumour cells have the potential to invade other cells or spread other parts of the body and this is called metastasis.