Pregnancy Does Not Lead to Breast Cancer Recurrence, Study Finds

Becoming pregnant does not increase a woman's chance of having her breast cancer recur, according to a recent study presented at ASCO.
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.

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