The link between exposure to dioxin and endometriosis: a critical reappraisal of primate data

Endometriosis is a common and enigmatic disease affecting women of reproductive age. In 1993, Dr. Sherry Rier and her colleagues reported a serendipitous finding that quickly sent a shock wave through the endometriosis research community. They found that rhesus monkeys exposed daily for 4 years to dioxin developed endometriosis, with incidence and severity related to dose. The study prompted more animal and epidemiologic studies regarding the link between dioxin exposure and endometriosis. Yet, 10 years after the first piece of evidence was reported, the primate data are still equivocal, and the human data supporting the dioxin-endometriosis association are scanty and conflicting. While many reviewers of the subject recognize the need for more data, other reviewers tend to discount negative studies when reviewing positive studies. In this paper, a critical reappraisal of all evidence from human and primate data is presented. While there is evidence suggesting that exposure to dioxin may facilitate the short-term survival of endometrial implants in non-human primates, this evidence is not supported by both human and non-human primate studies evaluating the relationship between dioxin exposure and the development of spontaneous endometriosis. Weighing all converging evidence, it seems that there are no solid, credible data available at this moment to support the hypothesis that dioxin exposure may lead to the development of endometriosis.