大多数的癌症是由环境和遗传因素相互作用而发生的，其中遗传因素本身只负责大约5％的癌症，而其余归咎于外界的环境因素，它们与遗传的和获得的易感性一齐起作用。环境中存在各种致癌剂，如烟草、某些食物成份、污染（空气。水、食品供应的污染）、某些药物、放射和感染因子等 Most cancers occur through the interaction of the environment and genetic factors, where genetic factors alone are responsible for about 5% of cancers, while the rest are due to external environmental factors that work together with genetic and acquired susceptibility. Various carcinogens exist in the environment, such as tobacco, certain food ingredients, pollution (air, water, contamination of food supplies), certain medications, radiation and infectious agents, etc.