Endogenous Carcinogenesis: The Role of Tumor Promotion

Abstract

That environmental factors are predominant in the causation of human cancer is now regarded as a fact. It has been variously estimated (1) that up to 80–90% of neoplasms in humans result from such factors. Diet and smoking probably account for the greatest proportion of these neoplasms, but infectious agents, industrial and occupational exposures, and ultraviolet radiation also play significant roles (2). Yet, with the exception of tobacco abuse as a direct causative factor in the development of bronchogenic and bladder carcinoma, the exact mechanism and proportion of cancers attributable to other agents is not clear. Furthermore, although endogenous hormonal factors play a role in the relationship of parity to breast cancer incidence (3) and possibly to ovarian cancer (4), endogenous factors in the causation of human cancer have only been hinted at. Henderson and his associates (5) have suggested that endogenous estrogens may play a significant role in the development of a number of human cancers. A role...