Effect of Thymectomy on the Induction of Skin Tumours by 3,4-Benzopyrene

Abstract

MANY tumours induced by chemical carcinogens¹ or viruses^2–4 have been shown to be antigenic in the syngeneic and even autochthonous host. The fact that antigenically ‘foreign’ tumours can grow progressively to kill their hosts suggests the existence of factors which compensate for the antigenic disadvantage of the tumour cells. Thus, perhaps, only tumours of weak antigenicity can progress whereas more strongly antigenic clones may fail to develop. Furthermore, tumour progression might be possible only when the host's mechanism for homograft immunity is either poorly developed, as in the new-born³, or depressed as a result of irradiation⁵ or of the chemical carcinogen itself. It is known that a wide variety of carcinogenic agents themselves depress various types of immune response, including the homograft reaction⁶. It has in fact been suggested that the biological raison d'être of homograft immunity may be to allow the body to eliminate antigenically foreign neoplastic clones as they arise and before they can spread⁷.