Research shows that in 70 to 90 % of cancer cases, the cause is external. Causal factors include bacteria, viruses, radiation, chemicals, pollution, diet, cigarettes, and betelnut.
根據研究，七成到九成癌症成因來自外來因素，例如：細菌、病毒的感染，放射線、化學物質的危害，空氣、水的汙染，食物及抽菸、嚼檳榔… … 等等。