Women who have had breast cancer are often told they should think twice about having a child because pregnancy could worsen their disease. But a major study by a Danish team, to be published this Saturday in The Lancet should help allay those fears: It found the risk of death among more than 5000 breast cancer survivors was no greater for those women who became pregnant.
Estrogens stimulate the growth of breast tissue, so in theory, the high estrogen levels associated with pregnancy could raise the risk of tumor recurrence or death in women who have had breast cancer. Earlier studies haven't found this to be the case, but they were plagued by self-selection: Women with more advanced tumors tend to avoid having babies, so those who did become pregnant may have had a better average prognosis.
The Danish team, led by epidemiologist Mads Melbye of the Statens Serum Institut in Copenhagen, was able to overcome this problem because Denmark keeps registries of its citizens' cancer outcomes and their childbearing histories. Thus the researchers could account for the severity of a woman's cancer when they analyzed the data. They looked at records for 5725 women under 45 treated for breast cancer between 1978 and 1995, 173 of whom became pregnant one or more times. The risk of recurrence or death from breast cancer in women with full-term pregnancies was not significantly different from that of women who didn't become pregnant. Nor did abortions or miscarriages increase the risk.
Although one study can't answer the question definitively, says Melbye, this result should "offer much assurance" to women who are considering having a child after being treated for breast cancer. "I certainly think this has brought us a long way because we have been able to control for a lot of factors," he says. But breast cancer surgeon Jeanne Petrek of the Memorial Sloan-Kettering Cancer Center in New York City notes that there are inherent weaknesses in such a retrospective study, such as the fact that breast cancer treatments have changed over time. The Danish study is "good and it's reassuring, but it's not the final word," Petrek says.