Possible enhancing effects of atrazine on growth of 7,12‐dimethylbenz(a) anthracene‐induced mammary tumors in ovariectomized Sprague–Dawley rats

Atrazine, one of the most commonly used herbicides in the world, has been reported to have endocrine disrupting effects in vivo. In the present experiment, influence of dietary atrazine on the late promotion/progression stage of mammary carcinogenesis in ovariectomized female Sprague–Dawley rats was examined after a single intragastric administration of 7,12‐dimethylbenz(a)anthracene (DMBA). When the incidence of palpable mammary tumors reached about 50%, the animals were subjected to ovariectomy and divided into tumor bearing [DMBA‐Tumor(+)] and non‐tumor bearing [DMBA‐Tumor(–)] groups, with subgroups of each fed a soybean‐free diet containing 0, 5, 50, or 500 p.p.m. atrazine for 34 weeks. At the completion of the study, the tumor volume in the 50 and 500 p.p.m. treatment Tumor(+) subgroups was greater than in the 0 p.p.m. control case. In the DMBA‐Tumor(–) group, higher incidences and volumes of the mammary tumors, with or without statistical significance (P