Cancer is a disease occurs due to abnormal cell division in the body. The abnormal cell proliferation occurs as a result of absence of cell division signal regulators. In other terms, cancerous cells lack the molecular components that instruct them to stop dividing uncontrollably and to die. The various chemical, cellular and environmental factors induce the tumour growth in the body. Exposure to certain substances have been linked to development of cancer such as smoking, excessive alcohol consumption, irregular lifestyle, obesity, exposure to radiation and infection with oncoviruses. Some cancers are also caused by herited genetic defects. Some hormones play an important role by promoting abnormal cell proliferation. Also, few autoimmune diseases are linked with cancer.
Factors causing cancer can be controlled and therefore, cancer is generally preventable. Greater than 30% of deaths from cancer can be prevented by avoiding risk factors such as tobacco, excess weight or obesity, poor diet and physical inactivity, unsafe sexual mating, and air pollution. Not all environmental causes are preventable, such as exposure to radiation and cancer caused through hereditary genetic defects.