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Researchers say it’s safe to pause long-term breast cancer treatment for pregnancy. Jon Vallejo/Getty Images
  • Researchers say it’s safe for women to pause long-term breast cancer treatment for up to 2 years for pregnancy and childbirth.
  • Experts say the new research provides valuable information for women who are concerned about delaying pregnancy to finish post-chemotherapy breast cancer treatments.
  • They note that a longer follow-up period of study participants is necessary.

Women in their childbearing years diagnosed with breast cancer typically take long-term medications that can prevent or delay getting pregnant.

Now, new research shows they might be able to pause their treatment for up to two years to get pregnant, have the baby, and breastfeed without raising their risk of having the cancer return.

The results of the study, led by Dr. Ann Partridge, MPH, a medical oncologist at the Dana-Farber Cancer Institute in Boston, were presented at the San Antonio Breast Cancer Symposium. They have yet to be published in a peer-reviewed journal.

The study followed 516 women who had surgery for breast cancer and then took hormone-blocking drugs for at least 18 months before stopping to get pregnant.

The women stopped for up to two years to have time to get pregnant, deliver, and breastfeed, then restarted their cancer therapy.

There were more than 300 babies born to women in the study.

For the study, women who opted to pause treatment completed between 18 and 30 months of hormonal therapy before the pause.

The scientists indicated that if 46 women had cancer recurrence within an average follow-up time of three years, they would suspend the trial. They did not reach that threshold. At the time that the study results were presented, 76% of the women had resumed treatment.

Three years after restarting cancer treatment, about 8% of the study participants experienced a recurrence of their cancer. Researchers said this is a similar level to what women who stay on cancer drugs experienced.

Nine deaths were reported during the study period. Researchers said this number was lower than expected.

“This confirms previous studies with the recurrence rate similar to women who did not stop treatment,” said Dr. Kecia Gaither, MPH, an OB/GYN in maternal fetal medicine and the director of Perinatal Service/Maternal Fetal Medicine at NYC Health + Hospitals/Lincoln in the Bronx.

“The results are consistent with previous retrospective and smaller clinical studies,” added Dr. Yung Lyou, a hematology-oncology specialist at the Hematology-Oncology Crosson Cancer Institute at Providence St. Jude Medical Center in California.

“This study helps change practice by providing a concrete method on how endocrine treatment interruption can be done safely and also provides strong evidence to support this statement,” Lyou told Healthline. “Overall. I would feel comfortable recommending taking a break from endocrine treatment for a patient who wants to become pregnant. The evidence I would cite would be from this study.”

The researchers plan to follow participants as they restart treatment to look at the long-term safety of pausing cancer therapy.

“This research is encouraging for young women who have had hormone-positive breast cancer and are committed to starting a biological family,” said Dr. Constance M. Chen, a plastic surgeon and breast reconstruction specialist in New York City.

“There is a relatively high frequency of congenital disabilities during tamoxifen treatment, so a washout period of 2 months is advised based on the known half-life of tamoxifen,” she told Healthline. “I would counsel her about risks and options if a woman got pregnant within 2 to 3 months after stopping the medication.”

Current treatments for endocrine-positive breast cancer include surgery plus long-term hormone-blocking medications and a monthly shot to stop the ovaries from making eggs.

However, the exact type of treatment that’s recommended can depend on the type of breast cancer and if and where it has spread.

The Centers for Disease Control and Prevention lists five significant types of treatment:

  • Surgery, which removes cancerous tissue
  • Chemotherapy that uses medications to kill or shrink cancer cells. Depending on the drugs, chemotherapy can be given via pills, intravenously, or both.
  • Radiation therapy, which uses high-energy rays to kill cancer cells
  • Hormonal therapy that uses medications that block cancer cells from getting the hormones needed for them to grow
  • Targeted therapy, which uses drugs that target specific aspects of cancer cells
  • Immunotherapy that works with your immune system to fight cancer cells

Many people receive a combination of two or more treatments. Your oncology team should provide you with information on the pros and cons of each type of treatment and work with you so you can make informed decisions about your care.

Treatment with hormone therapy for breast cancer can last anywhere from 5 to 10 years. Women put their desire to start a biological family on hold during treatment.

Younger women might find this an acceptable option. However, for women in their mid-30s or older, delaying getting pregnant for 5 or 10 years could mean losing the opportunity to have a biological family.

“It is very heartwarming to see a study that addresses this often unmet need of patients going through cancer—fertility and the process of recreating life after battling cancer,” said Dr. Bhavana Pathak, a hematologist and medical oncologist at MemorialCare Cancer Institute at Orange Coast Medical Center in California.

“It’s good to see the short-term recurrence rates of women who paused endocrine therapy be on par with those who continued therapy,” Pathak told Healthline.

The researchers noted that around 5% of new breast cancer diagnoses occur in women younger than 40. About 6,000 want to get pregnant in the United States and delay pregnancy while taking the drugs.

Whether or not to pause treatment and try to get pregnant is an individual decision.

“Every woman needs to base her decision about breaking from cancer treatment to have a baby on balancing her desire to have a biological child with her risk tolerance for breast cancer recurrence,” Chen said. “While the results of this study are encouraging when comparing breast cancer recurrence in women who stopped treatment for approximately two years to have a child with women who did not become pregnant, at the end of the day, every woman needs to make her own decision based on her personal goals and her risk tolerance level.”

Overall, the study found that the rate of congenital disabilities in women in the study was approximately 2%, which was about the same as for the public.

Generally, women who have been treated for endocrine-positive breast cancer do not have a higher risk of having a child with birth defects. However, waiting for the medicine to clear your body might be necessary.

“I have traditionally ensured that my patients use barrier protection as a means of birth control until their menses resume regularly for at least several months after stopping the hormone blocker therapy to reduce the risk of congenital disabilities,” said Dr. Lauren Carcas, a medical oncologist with Miami Cancer Institute, part of Baptist Health South Florida.

“However, the prior use of hormone-blocking agents and the risk of congenital disabilities has never kept me from discussing family planning with my patients with early-stage hormone receptor-positive disease who desire pregnancy,” Carcas told Healthline.

The study’s main limitation is the short follow-up period of 41 months. Breast cancer can recur many years after the original cancer diagnosis, so less than four years doesn’t provide sufficient data for doctors.

“The follow-up is relatively short for cancers that can recur years down the line, but it’s an excellent start,” said Dr. Parvin Peddi, a medical oncologist and director of Breast Medical Oncology for the Margie Petersen Breast Center at Providence Saint John’s Health Center and Associate Professor of Medical Oncology at Saint John’s Cancer Institute in California. “Patients should still be cautious and advised that we do not have long-term data. Therefore, the preference in a patient who can wait is to do so until they complete five years of endocrine therapy.”

“It’s reasonable to discuss interrupting endocrine therapy for carrying a pregnancy based on this study,” Peddi told Healthline. “I would also consider a given patient’s risk for cancer recurrence based on their breast cancer stage at diagnosis and other molecular characteristics of their cancer. For example, the scientists did not include stage III breast cancer patients due to their higher risk for recurrence.”