Experimental identification of genitourinary carcinogens.

Classic principles of pharmacology and toxicology are not entirely applicable to carcinogenesis. The existence of thresholds for carcinogens has yet to be proved. The use of high dosages in laboratory animals is an acceptable and necessary practice in identifying carcinogens. Generally, carcinogenicity is a result of the intrinsic property of a chemical and is independent of dosage and duration of exposure; however, the detection of carcinogenicity is dose-related. Not all chemicals are carcinogens. A properly designed and conducted study in laboratory animals is a scientifically valid way of identifying carcinogens that may pose a risk to humans. The route by which a chemical is administered to laboratory animals need not be identical to the way in which humans are exposed. The target organs in laboratory animals may or may not be the same as in humans. The inherent limitations of epidemiologic studies severely restrict their usefulness for detecting cancer-causing agents in human beings. Therefore, carcinogens identified in laboratory animals should be treated as if they cause cancer in human beings as well.