The majority of cancers (90 to 95 percent) are due to genetic mutations from environmental factors. The remaining 5 to 10 percent are due to inherited genetics, environmental factors such as lifestyle, economic and behavioral factors and not merely pollution. Common environmental factors that contribute to cancer death include tobacco diet and obesity, infections, radiation, both ionizing and non-ionizing stress, lack of physical activity and pollution. It is generally not possible to prove what causes a particular cancer because various causes do not have specific fingerprints. For example, if a person who uses tobacco heavily develops lung cancer, then it was probably caused by the tobacco use, but since everyone has a small chance of developing lung cancer as a result of air pollution or radiation, the cancer may have developed for one of those reasons. People with suspected cancer are investigated with medical tests. These commonly include blood tests, X-rays, contrast CT scans and endoscopy. This session discusses more about cancer causes and diagnosis.