Reflections on Second Annual NCTR Hormone Research Symposium.

Hormones have widely different effects depending on species, dosage use, timing of dosage, route of administration, status of animals (re: pregnancy, stage of estrous cycle, age), and end point being measured. Hormones are essential to both maintenance and quality of life, and they occur in our environment with regularity. Hormones are seen by some persons as a regulatory dilemma because, when characterized under conditions of marked overdosage, the biological consequences are often undesirable. Because many of the naturally occurring hormones were identified long ago and have been studied for many decades, the reality is that much more knowledge is available on hormones than on more recently discovered substances, either naturally occurring or synthetic. The effects of hormones on tumors, either increases or decreases in incidence, appear to be indirect through alterations of normal physiological processes. The mechanism of action of hormones at the cellular level suggests that hormones are not involved in cancer by causing DNA changes, but in the degree of expression of changes in DNA that have occurred by other means. Key studies, especially at the molecular level, to further define the involvement of hormones in carcinogenesis should help us to define tolerance levels and aid with the regulatory dilemma.