Infant mice given genistein developed cancer of the uterus later in life, scientists at the National Institute of Environmental Health Sciences (http://www.niehs.nih.gov) reported today. In the study, published in the June issue of Cancer Research (http://cancerres.aacrjournals.org/) , the scientists treated female mice for five days after birth with genistein, a substance in soy that is similar to the female hormone, estrogen.

"The data suggest that genistein is carcinogenic if exposure occurs during critical periods in a young animal's development," lead author Retha Newbold of NIEHS said.

In the study, newborn mouse pups were injected with an amount of genistein within the range similar to what a newborn human infant might receive in a soy-based infant formula. However, infants receive soy formula by mouth. Christopher Portier, Ph.D., National Toxicology Program (NTP) associate director said, "These data clearly suggest that more research is needed. NTP, in collaboration with the Food and Drug Administration (http://www.fda.gov) , is conducting further studies to confirm these findings, to find out whether cancers occur when genistein is given to rodents by mouth, to consider other similar agents, and to examine other possible multigenerational effects." NTP is headquartered at NIEHS in Research Triangle Park (http://www.rtp.org) , N.C.

NTP said, that because babies are often given soy formula for medical reasons, and because these results need further confirmation and evaluation, parents who have concerns about the use of soy formula should consult their pediatrician.

Kenneth Olden, (http://www.niehs.nih.gov/about/od/pastdirectors/) Ph.D., NIEHS/NTP director, said "This is part of a broad research effort by the NIEHS, the NTP, and our academic research centers to address critical data gaps in identifying the important environmental factors affecting children's health."

Co-authors with Newbold on the genistein study were Wendy Jefferson and Elizabeth Padilla of NIEHS, and Bill C. Bullock of the Wake Forest University School of Medicine (http://www.wfubmc.edu/) , Winston-Salem, N.C. (http://www.ci.winston-salem.nc.us/) .

The finding is similar to work Newbold did with diethylstilbestrol (DES) exposure in unborn mice. DES is a powerful synthetic estrogen, while genistein is a much weaker estrogenic agent made by plants. DES was previously given to pregnant mothers to prevent miscarriage and was used as a food additive to fatten chickens and cattle. All uses of DES in the United States have been discontinued because some children of mothers who took the drug during pregnancy developed rare cancers.