Although doctors previously worried that the body may produce enough extra estrogen during a pregnancy to trigger estrogen receptor positive breast cancer to return, a new study has calmed those concerns.
Breast cancers are designated estrogen receptor positive (ER+) or negative (ER-). When positive it means that the cancer grows and responds to the presence of estrogen.
"Pregnancy following breast cancer remission is safe."
Dr. Hatem Azim, Jr, a medical oncologist at the Jules Bordet Institute in Brussels, Belgium, led a study across several countries involving 333 women who became pregnant while in remission after having received a breast cancer diagnosis.
Azim and colleagues then compared this group's health data with 874 breast cancer patients of similar demographics who did not become pregnant and had not relapsed at the time that the women in the test group became pregnant.
The latter fact was intended to cancel out any confounding effect where the pregnant women may skew the results if they were healthier than the control group. The women ranged in age from 21 to 48 years old, with an average age of 34.
Approximately the same percentage of women in both groups had been treated with post-operative chemotherapy and hormonal therapy. The researchers also knew whether each of the women's estrogen receptor status was positive or negative.
The researchers tracked the women for an average of 4.7 years after the mother group's pregnancies, during which just under a third of all the women saw their cancer return.
Although a little over half the women - 57 percent - had estrogen receptor positive breast cancer, the researchers found no difference between the two groups of women in terms of how much time passed before the cancer returned. This was true regardless of whether the women had ER+ or ER- breast cancer.
The researchers also found slightly better outcomes among the women who became pregnant, though they caution that the findings may not accurately reflect any clear association between pregnancy itself and survival after remission.
"We found that patients who became pregnant within two years of breast cancer diagnosis appeared to have a better disease-free survival compared to those who did not become pregnant," Azim said. "However, a clear trend over time was not demonstrated."
Azim said it could be that the women who became pregnant may have been already more likely to live longer.
"This finding should be interpreted with caution, and hence pregnancy within two years of diagnosis should be regarded as safe, and not as protective," Azim said.
Choosing to breastfeed or not did not affect the women's likelihood of surviving longer for both ER+ and ER- disease, though the small number of women who breastfed - about 30 percent - was not sufficient for a strong conclusion. Neither did a pregnancy termination affect women's outcomes, so the doctors concluded that such a recommendation to women for the sake of beating the cancer is unwarranted.
"This is the first study to investigate the safety of pregnancy in breast cancer patients with ER+ disease, and which also adjusted for the 'healthy mother effect'," said Azim.
"It shows convincingly that pregnancy any time following breast cancer diagnosis is safe, irrespective of ER status," he continued.
"This study provides strong evidence to help proper counseling of women seeking to become pregnant following completion of breast cancer therapy. However, this study does not address the optimal duration of adjuvant hormonal therapy in these women."
The findings were presented March 20 at the eighth European Breast Cancer Conference in Vienna, Austria. The research was funded by grants from the European School of Oncology and the Les Amis de l'Institut Bordet.