#抗击癌症#癌症是由什么引起的？癌症源自一个单细胞。从一个正常细胞转变为一个肿瘤细胞要经过一个多阶段的过程，通常从癌前病变发展为恶性肿瘤。这些变化是一个人的基因因素与三种外部因素之间相互作用的结果，这些外部因素包括：1. 物理致癌物质，例如紫外线和电离辐射；2. 化学致癌物质，例如石棉、烟草烟雾成分、黄曲霉毒素（一种食品污染物）和砷（一种饮用水污染物）；3. 生物致癌物质，例如由某些病毒、细菌或寄生虫引起的感染。年龄的增长是癌症形成的另一个基本因素。癌症发病率随年龄增长而显著升高，极可能是由于生命历程中特定癌症危险因素的积累，再加上随着年龄的逐渐增长，细胞修复机能越来越差。知道癌症的起因能如何帮助你选择更健康的生活方式吗？了解更多，请点击（中文）：http://www.who.int/mediacentre/factsheets/fs297/zh/

#JointheFightAgainstCancer – What causes cancer? 

Cancer arises from one single cell. The transformation from a normal cell into a tumor cell is a multistage process, typically a progression from a pre-cancerous lesion to malignant tumors. These changes are the result of the interaction between a person's genetic factors and 3 categories of external agents, including: 1.) Physical carcinogens, such as ultraviolet and ionizing radiation; 2.) Chemical carcinogens, such as asbestos, components of tobacco smoke, aflatoxin (a food contaminant) and arsenic (a drinking water contaminant); 3.) Biological carcinogens, such as infections from certain viruses, bacteria or parasites. Ageing is another fundamental factor for the development of cancer. The incidence of cancer rises dramatically with age, most likely due to a build-up of risks for specific cancers that increase with age. The overall risk accumulation is combined with the tendency for cellular repair mechanisms to be less effective as a person grows older. How does knowing what causes cancer help you make better health choices?  To learn more, see (cn): http://www.who.int/mediacentre/factsheets/fs297/zh/