Copenhagen Rats Display Dominantly Inherited Yet Non-uniform Resistance to Spontaneous, Radiation-induced, and Chemically-induced Mammary Carcinogenesis

Abstract

Background/Aim: Genetic and environmental factors interact to dictate the risk of cancer, and animal models are expected to provide avenues for identifying such interactions. The aim of the study was to clarify the genetic susceptibility of Copenhagen rats to spontaneous, radiation-induced, and chemically-induced mammary carcinogenesis. Materials and Methods: Female Copenhagen and Sprague– Dawley rats and their F₁ hybrids were subjected at age 7 weeks to γ-irradiation or intraperitoneal injection with 1-methyl-1-nitrosourea or were not treated, and palpable mammary tumours were diagnosed histologically. Data were pooled with previous data acquired for both nontreated and irradiated Sprague–Dawley rats. Results: Radiation and 1-methyl-1-nitrosourea both significantly increased the incidence of mammary cancer in all strains. Copenhagen and F₁ rats displayed a significantly lower incidence than Sprague–Dawley rats in all groups, with relatively higher incidence after irradiation. F₁ rats exhibited significantly higher mammary cancer incidence than Copenhagen rats in the nontreated, but not the treated, groups. The interaction of the strain and exposure effects was suggested to be quasi-multiplicative. Conclusion: Copenhagen rats display non-uniform resistance to spontaneous, radiation-induced, and chemically-induced mammary carcinogenesis with dominant inheritance over Sprague–Dawley rats.