A new study supported by the US National Cancer Research body is set to investigate recent concerns that a growth promoter widely used in the US cattle industry could be linked to an increase in the risk of breast cancer. In the first-ever study of its kind, scientists will compare beef consumption with elevated levels of zeranol in women's blood, urine and breast tissue.
"We want our patients to know that we have no evidence suggesting that eating beef in any amount is dangerous," said Dr William Farrar, a breast cancer specialist at the Arthur G. James Cancer Hospital and Richard J. Solove Research Institute and a co-leader of the study. "But we are very interested in discovering any relationship between residual zeranol and enhanced oestrogenic activity in the breast. There is a lot to sort out here; this is just the first step."
Zeranol, one of several growth hormones allowed in the US but in fact banned in Europe, is commonly used throughout the cattle, veal and lamb industry in the United States. It is produced from the mould of a fungus often found in cereal and animal feed, and manufactured as a pellet that can be implanted under the skin of an animal's ear. Cattle growers use zeranol to help fatten the animals more quickly, create a higher lean-to-fat ratio and to develop meat with more flavour.
There is a body of scientific thought that maintains zeranol could be biologically active in stimulating breast cancer cell growth, however the US Food and Drug Administration maintains that it is safe to use in tiny amounts in young cattle and lambs.
In a statement this week Dr Young C. Lin, a veterinarian at the Ohio State University Comprehensive Cancer Center and a co-leader of the study, voiced his concerns. He pointed out that zeranol, although a synthetic non-steroidal agent, acts like oestrogen in the body. He claims that early laboratory studies suggest that zeranol, like oestrogen, stimulate oestrogen-modulated genes that can affect the growth of human breast cancer cells.
"We think this may be important, because some studies suggest that the more unopposed oestrogen a woman is exposed to over her lifetime, the greater her chances of developing breast cancer," said Lin.
Lin maintains that the key question is, does long-term, low-level exposure to zeranol add to that risk, or not?
"We have examined the impact of zeranol on the breast tissue of rats - and on human breast cancer cells, as well," he said. "Our research shows that even in very small amounts - levels 30 times lower than FDA approved limits, zeranol seems to enhance the effects of oestrogen." Although he cautioned that it is still far too soon to call beef products containing zeranol a potential environmental risk.
Lin and Farrar will examine both normal and cancerous breast tissue taken from patients at The James who undergo biopsy or surgical breast reduction. Volunteers will be asked to complete a questionnaire on beef consumption, and the patients will be classified according to the amount of beef they consume.
Researchers will take blood and urine samples to measure any residual zeranol against the activity of several biomarkers believed to be active in the development of breast cancer ( PTP, KGF, PR, pS2 and cyclin D1). The biological activity of the zeranol will also be measured by the degree of cell proliferation and alteration of oestrogen-responsive gene mRNA levels.
Lin and colleagues in veterinary colleges in four other universities across the country will simultaneously be collecting and testing random samples of supermarket-bought beef to gauge the presence and amount of zeranol residue in commercially available products. Partner institutions include the University of Minnesota, Texas A & M, Cornell University and the University of California at Davis.
Lin claims that the purpose of the study is not to challenge the legality of current regulations on the usage of zeranol in food animals, but rather to offer information that could be useful to regulatory agencies in decisions about the use of growth promoters used in beef destined for human consumption.
"We hope this study will permit an evaluation of the validity of the hypothesised link between long-term, low-level dietary exposure to zeranol in beef and adverse health effects, specifically with respect to breast cancer and other oestrogen-sensitive disorders," said Lin. "It is an issue that we are finally ready to address," he concluded.