CARcinogen definition
Definition. 1  A carcinogen is a substance that causes cancer (or is believed to cause cancer). 2  A carcinogenic material is one that is known to cause cancer. 3  The process of forming cancer cells from normal cells or carcinomas is called carcinogenesis. A carcinogenic material is one that is known to cause cancer. 2  The process of forming cancer cells from normal cells or carcinomas is called carcinogenesis.