MANY WOMEN WHO FINISH initial treatments for hormone receptor-positive breast cancer undergo around five to 10 years of endocrine therapy. This treatment blocks or reduces hormones that fuel cancer growth, such as estrogen. This limits the chances that breast cancer will return. However, for premenopausal women, endocrine therapy also can compromise the ability to conceive, greatly affecting their options for starting or expanding their families.
“This is a small but very vulnerable [patient] population that … wants to thrive in their survivorship, and having a baby after breast cancer is a really important thing for many [of these] young women,” says Ann Partridge, vice chair of medical oncology at Dana-Farber Cancer Institute in Boston.
Partridge recently led a study that found hormone receptor-positive breast cancer patients who paused their endocrine therapy in order to get pregnant are at no greater risk of cancer recurrence than women who don’t take a break from the therapy. The study, which Partridge presented at the San Antonio Breast Cancer Symposium in December 2022 and was published May 4, 2023, in the New England Journal of Medicine, followed women ages 27 to 43 who wanted to become pregnant. After being on endocrine therapy for between 18 and 30 months, they paused treatment for up to two years to try to conceive.
Of about 500 women, 74% had at least one pregnancy, and nearly 64% had at least one live birth. The pregnancy rates were high for people at the study’s median age of 37, Partridge says, noting about 43% of participants used fertility treatments. Additionally, Partridge says, babies born to these women had a low rate of birth defects, similar to babies born to women in the general population.
Three years after participants initially suspended their endocrine therapy, the rate of cancer recurrence was 8.9%—on par with recurrence rates for similar women who do not pause endocrine therapy.
“Previous studies had demonstrated safety in pregnancy post-treatment completion. This is the first prospective study to evaluate the pause on treatment and pregnancy,” says Alexandra Zimmer, director of the Breast Cancer Program at Oregon Health & Science University’s Knight Cancer Institute in Portland, who was not involved in the study.
However, hormone receptor-positive breast cancer can recur decades after diagnosis, according to Partridge. “This is relatively short-term follow-up [right now],” she says. “So while [the initial findings are] very reassuring, we need to watch this data set long term.”
For at least six more years, the researchers will continue tracking which participants get pregnant and experience cancer recurrences, as well as how they feel emotionally during pregnancy, after giving birth and while resuming endocrine therapy.
Young women diagnosed with hormone receptor-positive breast cancer are also at a higher risk for developing other breast cancers, according to Julie Gralow, chief medical officer and executive vice president of the American Society of Clinical Oncology, who was not a study author. So as the research continues, Gralow says, it’s important to investigate any local or distant recurrences of the same hormone receptor-positive breast cancer or any other subsequent breast cancers.
Partridge says initial safety data from this study can help reassure women with hormone receptor-positive breast cancer who worry pausing endocrine therapy for pregnancy could increase their risk of cancer recurrence. “Of course, there were women who did have their cancer come back, but it didn’t appear to be a higher risk of cancer coming back than in women who don’t interrupt [with] pregnancy,” she says.
“[These findings will] help lead [patients] back to the life they were planning on,” Gralow says.
“We want our patients to be treated and enjoy their life,” Zimmer says. “These findings, for now, mean that we are getting closer to that.”
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