Chemical carcinogenesis

This chapter discusses cancer that may be defined as a "malignant neoplasm" which defined literally is a strong new type of cellular growth that usually invades and takes over normal cellular tissue. The term "cancer" is sometimes only used to describe neoplasms of epithelial cells, such as the skin, and other malignant neoplasms of mesodermal cells, for example those of the bone, are described as "sarcomas." Cancer is probably the most serious disease affecting man. It is not, however, confined to man because most mammals and many other lower animals are affected. The seriousness of the disease is mainly a consequence of the difficulties of early diagnosis and treatment; even though these have been greatly improved during the last few years, cancer still presents formidable and often intractable problems. The role of certain viruses in causing some animal cancers has been decisively proved, but their role in the initiation of human tumors is still much disputed.