Hypertension in pregnancy cuts cancer risk.

Hypertension in pregnancy cuts cancer risk

During pregnancy, high blood pressure can signal toxemia, a condition characterized by metabolic disturbances of unknown cause that can threaten the lives of mother and baby. But new research suggests that mothers who weather hypertension during pregnancy may reap an unanticipated benefit -- a significant reduction in breast cancer risk.

Recent studies by Herbert I. Jacobson and his colleagues at Albany (N.Y.) Medical College showed that alpha-feto protein (AFP), produced in substantial amounts by the fetal liver, promotes the regression by estrogen-dependent breast cancers in rats. Since significantly elevated AFP levels have been found in the blood of hypertensive pregnant women, Jacobson teamed up with researchers at the Yale University School of Medicine to examine the breast cancer risk of such women. They compared information on hypertension for 4,668 women who developed breast cancer with that for 4,635 others matched by age and geographic region. All data had been collected from women 20 to 54 years old by the Atlanta-based Centers for Disease Control (CDC) as part of its Cancer and Steroid Hormone Study.

Compared with women who never developed high blood pressure or who became hypertensive only after child-bearing, those developing hypertension during at least one pregnancy ultimately experienced 28 percent fewer breast cancers, the team reports in the Oct. 18 JOURNAL OF THE NATIONAL CANCER INSTITUTE. A related study using the same set of data and described in the May AMERICAN JOURNAL OF EPIDEMIOLOGY showed that women whose most recent pregnancy involved twins experienced an even greater reduction -- 40 percent -- in breast cancer risk compared with women who had single births only.

With two fetal livers releasing AFP, a woman carrying twins will have double the normal blood level of AFP seen during pregnancy, explains epidemiologist W. Douglas Thompson, who led the most recent study. Though AFP measurements were not available for the women in the CDC data, "both studies indirectly support the idea that highly elevated AFP levels during pregnancy protect against breast cancer," says Thompson, now at the University of Southern Maine in Portland.

The Yale/Albany team "puts too much emphasis on AFP," argues University of Miami oncologist Niramol Savaraj, noting that "they have no data to substantiate that AFP is reducing the cancer risk." Thompson acknowledges the possibility that other pregnancy-associated factors led to the lower risk.

Jacobson, however, points out that the AFP released during pregnancy isn't inert, as many scientists once believed. His recent data show that AFP reacts with the most potent natural estrogen. This reaction, he says, converts AFP "into a new substance with hormone-like properties" that targets estrogen-responsive cells -- including some breast cancer cells. Jacobson says he has found that cultured human-breast-cancer cells are very sensitive to AFP. The amount "needed to turn off these [cancer] cells and their replication is less than a nonogram per milliliter," he says.