求翻译：癌症的产生原因是什么呢？国内外医学界已经证实，人类80%～90%以上的癌症与外部环境因素相关，也就是人类生活环境中的物理、化学和生物因素与癌症的发生密切相关。是什么意思？

What are the causes of cancer? Has been confirmed by the medical profession at home and abroad, more than human 80%~90% cancer associated with external environmental factors, that is, human life of physical, chemical, and biological factors in an environment closely associated with the occurrence of cancer.