Pregnancy Does Not Lead to Breast Cancer Recurrence, Study Finds

While doctors and patients alike often worry that a pregnancy could cause a breast cancer recurrence, a recent study found that is not the case.

A retrospective, multicenter study of 1,207 women treated for non-metastatic breast cancer who then became pregnant showed that these survivors faced no greater risk of recurrence or death than their counterparts who underwent treatment but did not become pregnant.

This was true even for women treated for estrogen receptor (ER)-positive disease, news that may assuage a common concern that pregnancy hormones could stimulate the growth of any estrogen-fueled cancer cells left in the body after treatment. Pregnancy after ER-positive breast cancer is also sometimes discouraged because it requires survivors to temporarily stop taking postsurgical hormonal therapy that is meant to prevent recurrence. That therapy typically continues for 5 to 10 years.

To date, its authors say, the study was the largest investigation of the effects of post—breast cancer pregnancy on recurrence risk and the first to consider the issue in women treated for the most common subtype, ER-positive disease. The findings were presented in a June 3 press briefing during the 2017 ASCO Annual Meeting.

“Our findings confirm that pregnancy after breast cancer should not be discouraged, even for women with ER-positive cancer,” said lead study author Matteo Lambertini, M.D., a medical oncologist and ESMO fellow at the Institut Jules Bordet in Brussels, Belgium. “However, when deciding how long to wait before becoming pregnant, patients and doctors should consider each woman’s personal risk for recurrence, particularly for women who need adjuvant hormone therapy.”

The news, which Lambertini said “should serve as a strong basis for counseling women inquiring into the safety of future conception,” could be life-changing for those who have undergone treatment for breast cancer and are in their reproductive years. Breast cancer is the most common oncologic disease in women of this age group, and while 40 percent to 50 percent of young women diagnosed with the disease report that they want to have children, less than 10 percent become pregnant after treatment, in part because of recurrence concerns, Lambertini said. Of all survivors of cancer, those treated for breast cancer are the least likely to have children after diagnosis, ASCO added.

“These data provide reassurance to breast cancer survivors that having a baby after a breast cancer diagnosis may not increase the chance of their cancer coming back. For many young women around the world who want to grow and expand their families, it’s very comforting news,” said ASCO Expert Erica L. Mayer, M.D., M.P.H.

Previously, the investigators conducted a study that showed no detrimental effect of pregnancy on breast cancer recurrence risk within the first five years following conception; this latest study provides follow-up data out to a median 12.5 years past conception, important because survivors of ER-positive disease face a risk of recurrence that exceeds five years, Lambertini said.

The study at centers across Europe enrolled women who were under the age of 50 when they were diagnosed with non-metastatic breast cancer prior to 2007. Among them, 57 percent had ER-positive disease, and more than 40 percent faced risks that could negatively affect prognosis, such as larger tumors or cancer that had spread to the axillary lymph nodes.

Of participants, 333 became pregnant and 874 did not; according to the study design, each pregnant participant was matched with three women who had similar tumor and treatment characteristics but did not become pregnant. Women who became pregnant conceived a median 2.4 years from diagnosis, although investigators found that those with ER-positive cancer tended to achieve pregnancy later than survivors with ER-negative disease.

Researchers found no meaningful difference in disease-free survival based on whether pregnancy had occurred, regardless of ER status. They further determined that disease-free survival was not affected by whether women had completed a pregnancy or had an abortion, became pregnant more or less than 2 years after diagnosis, or breastfed.

Looking strictly at survivors of ER-positive cancer, the researchers found no statistically significant difference in overall survival in those who became pregnant versus those who did not. Survivors with ER-negative breast cancer who became pregnant, however, gained an advantage: Researchers found that they had a 43 percent lower chance of dying than women treated for the same cancer who did not conceive. They also demonstrated about a 25 percent disease-free survival advantage over women with ER-negative breast cancer who did not become pregnant, although that trend was not considered statistically significant.

“It’s possible that pregnancy could be a protective factor for patients with ER-negative breast cancer, through either immune system mechanisms or hormonal mechanisms, but we need more research into this,” Lambertini said.

Further research will also be needed to learn the effects of pregnancy on the health outcomes of women with BRCA mutations, who when affected by the disease, generally develop it at a younger age.

The effects of interrupting postsurgical hormone therapy to allow for pregnancy in survivors of ER-positive breast cancer are being considered in a large clinical trial known as the POSITIVE study, the authors pointed out; they said that their own analysis provides further rationale for that study. POSITIVE will also shed light on the impact of reproductive technologies and breastfeeding.

Lambertini and colleagues identified some gaps in the information they used for their analysis. They noted that the study did not include much information on the use of assisted reproductive technologies, such as in vitro fertilization, in breast cancer survivors, and that, in the cases of 80 percent of participants, researchers did not know whether cancers fit into the HER2-positive disease subtype.

The study was partly supported by grants from Les Amis de l’Institut Bordet and the European School of Oncology. The International Breast Cancer Study Group study, which provided patient information for this study, was partially funded by the National Institutes of Health.