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Pregnancy does not increase the risk of dying from breast cancer, study published in JAMA Oncology finds


Pregnancy does not increase a woman’s risk of dying from breast cancer, Women’s College Hospital (WCH) and Institute for Clinical Evaluative Sciences (ICES) scientists have found in a new study published today in JAMA Oncology. This study is the largest study to date on the subject.

More women are having babies in their late 30s and early 40s, and in rare cases, they are diagnosed with breast cancer around the time of pregnancy. Some studies have suggested that pregnancy around the time of breast cancer diagnosis may increase the risk of death. The current study found that the five-year survival rates for women who were not pregnant and women who were pregnant around the time of breast cancer diagnosis were similar.

The study was led by Steven Narod, MD, FRCPC, PhD (hon), FRSC, Women’s College Hospital senior scientist, director of the familial breast cancer research unit and a Tier One Canada Research Chair in Breast Cancer.

Some doctors now recommend that women wait two years before becoming pregnant after they finish treatment for breast cancer. The new study suggests those women need not delay their pregnancy.

“We think that a pregnancy at the time of breast cancer does not pose a risk to the mother,” Dr. Narod said.

The study used administrative databases from ICES, incorporating data on age, cancer stage, treatment and survival of more than 7,500 breast cancer patients between the ages of 20 and 44 in Ontario between 2003 and 2014.

The study found the five-year overall survival was 87.5 per cent for women with no pregnancy, 82.1 per cent for women with pregnancy-associated breast cancer and 96.7 per cent for women who had pregnancy six months or more after diagnosis of breast cancer. The difference between pregnancy groups was not significant.

The researchers found the early age at diagnosis was associated with more aggressive breast cancers, but it was not the pregnancy that was the risk factor.

“We know that breast cancers in young women are more aggressive and have a higher risk of recurring,” Dr. Narod says. “Our work shows that we need more studies to understand why younger women fare worse, and how to help them recover from breast cancer.”

Women’s College Hospital
For more than 100 years Women’s College Hospital (WCH) has been developing revolutionary advances in healthcare. Today, WCH is a world leader in the health of women and Canada’s leading, academic ambulatory hospital. A champion of health equity, WCH advocates for the health of all women from diverse cultures and backgrounds and ensures their needs are reflected in the care they receive. It focuses on delivering innovative solutions that address Canada’s most pressing issues related to population health, patient experience and system costs. The WCH Institute for Health System Solutions and Virtual Care (WIHV) is developing new, scalable models of care that deliver improved outcomes for patients and sustainable solutions for the health system as a whole.

Women’s College Research Institute (WCRI) is tackling some of the greatest health challenges of our time. Its scientists are conducting global research that advances the health of women and improves healthcare options for all, and are then translating those discoveries to provide much-needed improvements in healthcare worldwide.
For more information about how WCH and WCRI are transforming patient care, visit www.womenscollegehospital.ca and www.womensresearch.ca

The Institute for Clinical Evaluative Sciences (ICES) is an independent, non-profit organization that uses population-based health information to produce knowledge on a broad range of healthcare issues. Our unbiased evidence provides measures of health system performance, a clearer understanding of the shifting healthcare needs of Ontarians, and a stimulus for discussion of practical solutions to optimize scarce resources. ICES knowledge is highly regarded in Canada and abroad, and is widely used by government, hospitals, planners, and practitioners to make decisions about care delivery and to develop policy. For the latest ICES news, follow us on Twitter: @ICESOntario


Magdalena Stec
Communications Lead, Strategic Communications
Women’s College Hospital
[email protected]
(416) 323-6400 ext. 3210

Deborah Creatura
Media Advisor, ICES
[email protected]
(o) 416-480-4780 or (c) 647-406-5996

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