Debating BST 'til the cows come home.

Milk from cows receiving a drug that boosts their milk production puts people who drink it at greater risk of developing breast and colon cancer, contends a new report by a long-time opponent of the drug.

The Food and Drug Administration continues to consider the milk safe, an agency spokesperson said this week in response to the allegations.

In November 1993, the FDA approved the sale of milk from cows treated with recombinant bovine somatotropin (rBST), a genetically engineered version of a naturally occurring growth hormone. Most dairy products sold in the United States now include at least some milk from rBST-treated cows.

Samuel S. Epstein, a physician at the University of Illinois at Chicago School of Public Health, has reviewed 66 studies relating to rBST milk and concludes that they "raise very significant questions about the carcinogenic risks" of the liquid. He spoke this week in Washington, D.C., at a press conference organized by the Cancer Prevention Coalition, which he chairs, and Food & Water, a consumer group in Walden, Vt.

Officials from FDA and Monsanto Co., which produces the drug, accuse Epstein of rehashing concerns he raised in 1994, which they reviewed and disputed at the time. Epstein's report includes no original data and cites no references published after 1994.

Studies show that milk from cows treated with rBST has a high concentration of insulinlike growth factor-1 (IGF-1), Epstein asserts. Furthermore, he argues, IGF-1 can increase humans' risk of developing breast and colon cancer. The protein occurs naturally in human blood and milk.

Among the studies Epstein reviewed are summaries released by FDA of six unpublished industry reports. They show that the concentration of IGF-1 in rBST milk ranges from 25 to 70 percent above the amount in milk from untreated cows, Epstein reports in the January International Journal of Health Services. Moreover, many studies used "flawed analytic techniques that underestimate IGF-1 levels . . . resulting in a potential 40-fold underestimate."

Pasteurizing milk increases the IGF-1 content by 70 percent, he says. Epstein cites studies suggesting that IGF-1 stimulates the growth of both normal and cancer cells. Evidence of its involvement in breast cancer comes from reports that blood and malignant tissue of breast cancer patients have high concentrations of IGF-1.

Epstein links IGF-1 to gastrointestinal cancer, citing laboratory studies that the protein, in amounts equivalent to those occurring in milk from untreated cows, stimulates the proliferation of intestinal cells. Adding IGF-1 therefore increases the possibility that milk will cause normal and cancer cells to divide in the human gastrointestinal tract, Epstein argues. Unlike most proteins, IGF-1 reaches the gut intact, without being broken down into amino acids, he claims.

"This is deja vu all over again . . . it's amazing how many ways [Epstein] can try to say the same thing," asserts FDA spokesman Don McLearn. "To raise unsubstantiated fears in people's minds is irresponsible," says Gary F. Barton, director of biotechnology communications for Monsanto in St. Louis. IGF-1 "in human breast milk is at about the same concentration as that found in bovine milk" from treated and untreated cows, FDA's Richard H. Teske wrote Epstein in March 1994. Newer studies also show that milk from cows treated with IGF-1 does not have a high concentration of the protein, argues Stephen F. Sundlof, director of the FDA office that approved the drug.

Even if the milk had extra IGF-1, it wouldn't pose a risk, contends Sundlof. He disputes Epstein's claim that IGF-1 survives in the intestine. Moreover, other proteins in human blood would bind to and inactivate most IGF-1 that entered the bloodstream, he holds.

"There is no evidence that IGF-1 induces the malignant transformation of normal breast cells," Teske's letter argued. No such evidence has surfaced since 1994, Sundlof adds.