I have looked into this matter and what I found was a 2001 letter in the Journal of the National Cancer Institute highlighting this as a concern:
http://jncicancerspectrum.oupjournals.org/...l/jnci;93/3/238
but also the U.S. FDA's arguments arguing that this was not a problem:
http://www.fda.gov/cvm/index/bst/RBRPTFNL.htm
The European Union has banned the use of milk-production producing hormones. Reports at the time indicate that this ban was initially put in place out of concerns that consumers would stop milk out of a concern over the hormones and because it would undermine agricultural policy. When a permanent ban was imposed, according to a press report the relevant committee "concluded that the risk to human health from drinking milk from rBST-treated cows was likely to be extremely small but could not
be ruled out entirely without further studies. The Committee also concluded that the treatment of dairy cows with rBST is associated with welfare problems, notably decreased body condition, an increased risk of mastitis, lameness and injection site lesions." It was primarily these animal welfare concerns that led to the product being banned. I suspect, too, that there is something to fears about consumer resistance to hormones in food, because I live in England and after the mad cow crisis people are very skittish about any unnatural food practices, no matter what the science says.
I just thought it was important to point out that there is some doubt over the matter.
Hybrid Mode
