在70年代,由于认识到生产和使用石绵和氯化乙烯的一些工人可患恶性肿瘤,因而职业在诱发癌中的作用更显得越来越重要。这些发现标志着职业性环境致癌物的探讨和予防问题已进入了新时代。环境因素致癌的诱发率可高达70％(Higginson,1968)和90％(Boyland,1969)。其后癌症的发病率有所降低,主要取决于对环境因素的控制。美国国家职业保键 In the 1970s, the role of occupations in the induction of cancers became even more and more important given the recognition that some workers who produce and use asbestos and vinyl chloride can develop malignancies. These findings indicate that the probe into occupational environmental carcinogens and the prevention issue have entered a new era. Induction of environmental causes of cancer can be as high as 70% (Higginson, 1968) and 90% (Boyland, 1969). Subsequent decline in the incidence of cancer, mainly depends on the control of environmental factors. U.S. National Occupation Key