Carcinogenesis: Mechanism and Criteria of Carcinogenic Activity.

The pattern of carcinogenic action is described for locally acting as well as for remotely acting carcinogens. Whether applied locally, injected subcutaneously or given by mouth, aromatic polycyclic hydrocarbons are potentially carcinogenic for all tissues, whereas other known locally acting carcinogens have no such wide action. Solubility and diffusibility of the compound should be considered, but the question of localization of induced tumours is a problem of dose-response relationship.The method for evaluating carcinogenic action of a compound is based on the readiness with which the tumour is induced, and not in terms of the intensity of the response. The average latent period and the percentage of tumour yield are the two measures used. Since, at the present time, no chemical tests are available to determine whether a substance is carcinogenic, one must resort to biological methods of testing carcinogenic activity.The value of a long-term test for carcinogenesis, under a given set of rigidly controlled conditions, is emphasized, since there are so many variables which singly or in combination may alter the final effect of a given substance.