Women can safely interrupt hormone therapy to have a baby, study finds

Long-awaited findings from a study looking at pregnancy and breast cancer medication is bringing reassurance to patients and specialists alike.

Women with hormone-receptor positive tumours take a daily pill for up to 10 years following their diagnosis to reduce their risk of the cancer returning.

As this treatment, called endocrine therapy, supresses oestrogen production, it can impact fertility. For many young women diagnosed with breast cancer who have not completed their families, deciding whether to start endocrine therapy is frequently reported as one of the biggest challenges they face.

However, this new study has found that it is safe to stop long-term treatment, like tamoxifen, temporarily in order to have a baby. These results were presented at the San Antonio Breast Cancer Symposium, the world’s most prestigious breast cancer conference, in Texas, United States earlier in December.

It is the first study to look at interrupting endocrine therapy to attempt pregnancy.

It included 518 women aged 42 or younger, diagnosed with stage one to three breast cancer, who had been on endocrine therapy for at least a year and a half before stopping treatment to try and get pregnant. They were encouraged to wait no more than two years before resuming their therapy.

Of the study participants, 63% were able to get pregnant and have a baby, and more than 75% have now returned to their endocrine treatment.

Study lead and professor of medicine at Harvard Medical School Ann Partridge says that within three years of stopping hormone-suppressing drugs, the rate of breast cancer recurrence was 8.9% - which is similar to the rate expected for patients who stuck with the medication consistently.

Other breast cancer specialists told NBC News the study results will be practice-changing for them and their patients.