Breast cancer is the most frequent
malignancy diagnosed in women and is a classical model of
hormone-dependent
malignancy. Over the past 15-20 years, epidemiological studies have pointed to an increased
breast cancer risk associated with prolonged exposure to female
hormones. On the other hand, environmental chemicals such as
malathion, an organophosphorous
pesticide used to control a wide range of sucking and chewing pests of field crops, may be involved in the etiology of breast
cancers. Results indicated that
estrogen alone increased average number of lobules per mm2 of rat mammary glands in comparison to control and
malathion alone at 30, 124, 240 and 400 days after 5-day treatments. On the other hand,
malathion alone significantly increased the number of ducts in stage of proliferation
at 10-240 days after 5-day treatments. Furthermore, markers for
cancer detection such as mutant p53, c-myc, c-fos and CYPs
proteins were overexpressed
after treatments.
Atropine, an
anticholinergic drug, counteracted these effects when it was combined with
malathion under similar conditions. The combination of
malathion and
estrogen synergistically increased number of lobules and ducts per mm2 of rat mammary glands
after treatments and inducing
mammary cancer. It can be concluded that combination of an environmental substance such as the
pesticide malathion and an endogenous substance such as
estrogen can enhance the deleterious effects in human mammary glands inducing
cancer and
atropine is able to diminish these effects.