Previous workers comparing exposure to metallic air pollutants to breast tumour estrogen and progesterone receptor status have reported either that arsenic and cadmium exposure increase ER/PR-negative cancer risk [12], that mercury, antimony and cobalt increase ER-positive cancer risk [24], and that cadmium, antimony and cobalt increase ER/PR-negative cancer risk [22]. The gene discussed is PGR; the disease is breast neoplasm.