 Some scientists doubt that xenoestrogens have any significant biological effect, in the concentrations found in the environment.However, there is substantial evidence in a variety of recent studies to indicate that xenoestrogens can increase breast cancer growth in tissue culture.It has been suggested that very low levels of a xenoestrogen, Bisphenol A, could affect fetal neural signalling more than higher levels, indicating that classical models where dose equals response may not be applicable in susceptible tissue.