Recently, ZON and its metabolites have become of great interest
because evidence suggests that they may play an important
role in increasing the risk of hormone-dependent tumors.
In vitro studies
show that these compounds enhance proliferation of estrogen
receptor-positive human breast tumor cells, through estrogenmediated
pathways and by activation of gene profiles similar to
those activated by natural estradiol (Khosrokhavar et al., 2009;
Parveen et al., 2009).
Regarding in vivo studies, exposure of
female rats to environmentally relevant doses of ZON resulted
in long-term changes in mammary gland development, associated
with increased risk of mammary tumors.
In
addition, serum collected from heifers following one month of
a-ZAL implantation stimulated MCF-7 breast cancer cell growth.