BARCELONA — If women who have been successfully treated for breast cancer become pregnant, they are not putting their lives at risk, according to a large meta-analysis. Indeed, investigators found evidence that pregnancy in breast cancer survivors may confer a protective effect on overall survival.
“There is a wide perception in the oncology community that women with a history of breast cancer should not get pregnant,” Dr. Hatem A. Azim Jr. said at the European Breast Cancer Conference. “This meta-analysis strongly argues against this notion.”
The meta-analysis included 14 trials, published between 1970 and 2009, that involved more than 19,000 women with a history of breast cancer; 1,417 were pregnant and 18,059 were not pregnant at the time of study. Women who became pregnant after breast cancer treatment had a 42% decreased risk of dying compared with those who did not get pregnant. Tests for publication bias and heterogeneity did not reach statistical significance.
“Our findings clearly show that pregnancy is safe in women with a history of successfully treated breast cancer,” said Dr. Azim of Institut Jules Bordet in Brussels. He described three hypotheses as to why pregnancy might have a protective effect in breast cancer survivors:
▸ Women with breast cancer who later became pregnant were more likely to be healthy and less likely to experience recurrences. Dr. Azim noted that data from at least three studies controlled for women who relapsed at the time of pregnancy, and a protective effect of pregnancy was still observed.
▸ Hormonal effects could be involved, with some evidence that beyond a certain threshold, estrogen has an inhibitory effect on hormone receptor–positive tumor cells. High prolactin levels have been linked to a lower risk of breast cancer recurrence.
▸ There is the concept of alloimmunization, with the possibility that fetal antigens shared by tumor cells stimulate an immune response in the mother.
Further analyses are planned. “The take-home message is that women who want to get pregnant following breast cancer can do so—it's safe,” Dr. Azim said.
“There are many guidelines but not much guidance,” said Dr. Mike Dixon, clinical director of the Breakthrough Breast Cancer Research Unit in Edinburgh. “The meta-analysis … does show better survival in women who become pregnant,” he said, but he expressed concern that there was a selection bias in the trials and that further information was necessary.
Dr. Azim and Dr. Dixon reported no relevant conflicts of interest.