History of Identification of Human carcinogens .The carcinogenic effects were first described in humans .In the 20th century experimental animals has preceded evidence from epidemiologic or case studies in humans The majority of human cancers probably result from the interaction of carcinogen along with intrinsic factors•The carcinogenic effects were first described in humans. •In the 20th century, experimental animals has preceded evidence from epidemiologic or case studies in humans. •The majority of human cancers probably result from the interaction of carcinogen along with intrinsic factors. History of Identification of Human Carcinogens