procarcinogen The precursor of an active carcinogen. The procarcinogen itself is not usually carcinogenic but is converted to the active carcinogen after it has been metabolized. For example, the drug diethylstilboestrol (a synthetic oestrogen no longer in clinical use) is metabolized to an epoxide intermediate, which can cause cervical cancer.

procarcinogen A compound that is not itself carcinogenic, but undergoes metabolic activation in the body to yield a carcinogen.