Xenoestrogen
Xenoestrogens are a type of xenohormone that imitates estrogen. They can be either synthetic or natural chemical compounds. Synthetic xenoestrogens include some widely used industrial compounds, such as PCBs, BPA, and phthalates, which have estrogenic effects on a living organism even though they differ chemically from the estrogenic substances produced internally by the endocrine system of any organism. Natural xenoestrogens include phytoestrogens which are plant-derived xenoestrogens. Because the primary route of exposure to these compounds is by consumption of phytoestrogenic plants, they are sometimes called "dietary estrogens". Mycoestrogens, estrogenic substances from fungi, are another type of xenoestrogen that are also considered mycotoxins.
E-SCREEN
The gain of the number of human breast cancer cell is biologically identic to the rise, in tissues of the genital tract, of the mitotic activity such as the rodent endometrium. In the 1930s, a new screening test called the uterotrophic bioassay was created, but it was not until 1962 that was firstly normalized by an expert committee. This assay quantifies the addition of uterine wet weight or the intensification of uterotrophic response and, additionally, it measures vaginal cornification. The test estimates a chemical’s ability to evoke biological activities in accord with agonists or antagonists of endogenous estrogens (e.g. 17ß-estradiol); nevertheless, its use for agonists investigation is much more ordinary than for antagonist. 
The uterus responds to estrogens in two ways:
The uterus responses in rats and mice can be qualitatively compared.Exposure to estrogens (xenoestrogens) may be also easily assessed in fish, reptiles or birds by measuring their vitellogenin (VTG) plasma levels. An example is that expression of the egg yolk precursor protein vitellogenin can be measured by the E-SCREEN test in juvenile brown trout. Usually, vitellogenin is only produced by female fish, because it is estrogen-dependent. Nevertheless, the synthesis of this protein in males and young fish can also occur, as xenoestrogens can also affect the hepatic receptors and activate it. Hence, a frequently used biomarker of exposure to estrogen active substances in the environment is the measurement of vitellogenin levels in male and juvenile trout.