The present workshop had its orlglns in discussions among Alexander Hollaender, Oddvar Nygaard, Donald Borg, Richard Setlow and Victor Bond on the need for a symposium that would deal with a broad spectrum of pressing subjects related to the physics, chemistry, and biological actions of ionizing radiations, and the theoretical and practical problems of risk assessment. It soon became apparent that the spectrum of subjects considered was too broad for the desired depth of coverage; in fact, it seemed un likely that the conference participants would have the background knowledge to span the gamut. Therefore, two separate meetings were decided upon, the first of which, Comparison of Mechanisms of Carcinogenesis by Radiation and Chemical Agents, was held at the National Bureau of Standards, Gaithersburg on December 6-7, 1983. The meeting was sponsored by the NCI. The second meeting has emerged as the present workshop at Brookhaven National Laboratory. An interface between the two conferences has been provided by Michael Fry and Donald Borg, who have summarized the salient points emanating from the NCI Symposium. We intended that the first conference should focus on the basic mechanisms of radiation and chemical carcinogenesis, while the second, the present meeting, would emphasize exposure-response relationships, particularly the theoretical and practical similar ities and differences between exposure to chemical carcinogens compared to exposure to ionizing radiation.

Inhalt
Dedication.- Keynote Address.- Epidemiological Reservations about Risk Assessment.- Report of National Cancer Institute Symposium: Comparison of Mechanisms of Carcinogenesis by Radiation and Chemical Agents.- I. Common Molecular Mechanisms.- II. Cellular and Animal Models.- Theoretical Aspects.- What Are We Doing When We Think We Are Doing Risk Analysis?.- The Control of Mutagenesis and Cell Differentiation in Cultured Human and Rodent Cells by Chemicals That Initiate or Promote Tumor Formation.- The Role of Mechanistic Data in Dose-Response Modeling.- Statistical Aspects of the Estimation of Human Risks.- Biological Mechanisms: Single Cells.- The Isolation and Characterization of the Blym-1 Transforming Gene.- Retroviral Oncogenes and Human Neoplasia.- Mutation in Single-Cell Systems Induced by Low-Level Mutagen Exposure.- Quantitative Neoplastic Transformation in C3H/10T1/2 Cells.- Modification of the Response.- Risk Estimate for Genetic Effects.- Saturation of Repair.- Role of Tumor Promotion in Affecting the Multi-Hit Nature of Carcinogenesis.- Genetic and Epigenetic Aspects of Tumor Progression and Tumor Heterogeneity.- Biological Mechanisms: Cells to Animals.- Interaction of Ionizing Radiation and 8-Methoxypsoralen Photosensitization: Some Implications for Risk Assessment.- Low-Level Exposures to Chemical Carcinogens: Mutational End Points.- Radiogenic Neoplasia in the Thyroid and Mammary Clonogens: Progress, Problems and Possibilities.- Induction and Manifestation of Hereditary Cataracts.- The Human Experience: Models to Humans.- Extrapolation from Large-Scale Radiation Exposures: Cancer.- The Feasibility and Urgency of Monitoring Human Populations for the Genetic Effects of Radiation: The Hiroshima-Nagasaki Experience.- Prospects for Cellular Mutational Assays in Human Populations.- Cytogenetic and Allied Studies in Populations Exposed to Radiations and Chemical Agents.- Round Table Discussion.- Where the Future? Part I.- Where the Future? Part II.- Fons et Origo.- The Agent Carrier and Transfer Approach to Radiobiological Responses.- Participants 507.