Chemical carcinogenesis is currently regarded as a complicated series of events requiring initiation and promotion in specific sequences. Carcinogens are thought to be be chemicals which can induce both initiation and promotion so that few if any additional host or environmental factors are required in the production of neoplasms. Most experimental studies to date have investigated bladder cancer using these highly active agents and the role of other substances in urothelial neoplasia has not been emphasized. We have examined the role of a variety of solutions, including water and saline, in pilot studies of urothelial carcinogenesis using the ALZA mini-pump for continuous infusion. Bladder tumors indistinguishable morphologically from papillary transitional cell carcinomas were induced. Although experimental induction of bladder cancer with powerful carcinogens may completely overwhelm host defenses and result in more and higher grade neoplasms, similar tumors may occur after exposure to substances not generally considered to be carcinogenic. This process, which probably requires cofactors and host-chemical interaction, may be more representative of environmental carcinogenesis than systems using powerful carcinogens and should be further investigated.
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