An unfair reality is that breast cancer is the most common type of cancer to afflict young women, meaning women of childbearing potential. Until recently a diagnosis of breast cancer, particularly estrogen receptor (ER)-positive disease, often meant the patient would decide against having children and her doctor would agree with her. Patients with ER-positive breast cancer and their physicians worried about interrupting adjuvant hormone therapy before attempting to conceive. Adjuvant therapy, which can prevent cancer recurrence, is recommended for 5 to 10 years after completion of acute treatment. An often crucial period of time for women who wish to have a child.

The breast cancer-pregnancy conundrum is particularly significant. Although approximately half of young patients with newly diagnosed breast cancer look forward to raising a family, only 10% or fewer actually choose to have a child after receiving their diagnosis. The specter of pregnancy increasing their chance of the cancer returning was enough to prompt most of these young survivors to change their plans.

However, findings from a new study has shed some hope on this plight. Although pregnancy does cause a surge in estrogen levels, these findings show that the process does not stimulate the growth of occult cancer cells following treatment. Matteo Lambertini, MD, an oncologist at the Institut Jules Bordet in Brussels, Belgium, presented the findings from this study in a poster presentation at the 2017 American Society of Clinical Oncology Annual Meeting. 

The retrospective analysis, comprised of data from 1207 women in the United States and across Europe, is the largest study to evaluate the extent of risk posed by pregnancy after breast cancer. Importantly, it was the only study to investigate the safety of pregnancy after ER-positive breast cancer. Eligible participants had to have received a diagnosis of nonmetastatic breast cancer before age 50 years. ER-positive tumors were diagnosed in 57% of the women, and more than 40% had poor prognostic factors such as axillary lymph node involvement and large tumor size.

Impact on Pregnancy

Of the participants in the trial, 333 women became pregnant an average of 2.4 years after their cancer diagnosis. The women who had ER-positive cancer were more likely to conceive later than the women with ER-negative disease. Once a participant became pregnant, the case-control study design specified that she be matched with 3 participants who were not pregnant but whose cancer characteristics were similar.