Xenoestrogen
Xenoestrogens are clinically significant because they can mimic the effects of endogenous estrogen and thus have been implicated in precocious puberty and other disorders of the reproductive system.
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.