Prophylactic cancer chemotherapy may have first trials soon The first clinical trials in cancer chemoprevention could begin within a year under the auspices of the National Cancer Institute (NCI), in Bethesda, Md. The idea of cancer chemoprevention is to use pharmacologic means to stop or reverse preneoplastic changes in tissue before the ultimate progression to tumor formation becomes irreversible. The principal chemical to be tested could be 13-cis-retinoic acid, a synthetic analog of vitamin A, that would be administered to persons at high risk of cancer. "I think there are people in the United States at sufficiently high risk of cancer that one could justifiably consider the possibility of putting them on a regimen of 13-cis-retinoic acid on a prophylactic basis," says Michael B. Sporn, MD, chief of the Lung Cancer Branch at NCI. Among the possible candidates for such treatment are asbestos workers and