CANCER CAN STRIKE almost any living thing. Not only mammals but birds, fish, and insects get cancer. Tumors have been found in dinosaur bones, and cancerlike growths appear in plants as well. It could be said that where there is life, there is cancer.

Human beings can get over two hundred kinds of cancer, and each kind is really a different disease. Some progress more rapidly than others and present a greater threat to life. Some are difficult to treat, while others can almost always be cured completely. "We haven't reached where we would like to be in [treating and understanding] cancer . . . because cancer is extraordinarily complex," says Richard Klausner, the director of the National Cancer Institute, one of the government-sponsored National Institutes of Health in Bethesda, Maryland. Despite their differences, however, all cancers have certain features in common.

Wildly dividing cells