Tobacco use is the cause of about 22% of cancer deaths.[1] Another 10% are due to obesity, poor diet, lack of physical activity or excessive drinking of alcohol.[2][2][3] Other factors include certain infections, exposure to ionizing radiation and environmental pollutants.[4] In the developing world, 15% of cancers are due to infections such as Helicobacter pylori, hepatitis B, hepatitis C, human papillomavirus infection, Epstein–Barr virus and human immunodeficiency virus (HIV).[2] These factors act, at least partly, by changing the genes of a cell.[5] Typically, many genetic changes are required before cancer develops.[11] Approximately 5–10% of cancers are due to inherited genetic defects from a person's parents.[6] Cancer can be detected by certain signs and symptoms or screening tests.[2] It is then typically further investigated by medical imaging and confirmed by biopsy.[7]