Cancer is a disease that is caused when cells in the body divide in an uncontrollable manner. It occurs due to uncontrolled cell division. 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. It is generally the absence of some cell division checkpoints or absence of gene regulation. 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; some cancer caused by exposure to certain chemicals that induce the production of cancerous cells and are also called carcinogenic agents. Exposure to radiations can also cause cancer. 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 pars of the body. Malignant tumour cells have the potential to invade other cells or spread other parts of the body. This is called metastasis.