Pregnancy and breast cancer impact each other in many ways. Whether you are cancer-free, newly diagnosed or a long-term survivor, you may have questions about how having children and breast cancer may be related. Understanding how childbearing impacts your breast cancer risk, and for survivors, how it relates to the chances of survival after treatment is important. And, for newly diagnosed younger women, understanding how some therapies may affect your fertility may be helpful in exploring options for having a child after treatment ends.
Pregnancy and breast cancer risk
Pregnancy is a time of breast development and hormone changes, so it is not surprising that it affects your breast cancer risk. However, this relationship is complex. Both the age when you give birth to your first child and the number of children you give birth to affect your risk.
How does age at the birth of a first child affect your breast cancer risk?
Although a first pregnancy may increase the short-term risk of breast cancer, it lowers the long-term risk. Pregnancy’s effects depend on your age when you first give birth.1-3
Women who have their first child at age 35 or younger tend to get an overall protective benefit from pregnancy. Breast cancer risk is slightly increased for about 10 years after a first birth. After that, it drops below the risk of women who don’t have children. The younger you are when you have your first child, the sooner you get the risk reduction benefit.2-3
Women who have their first child at later ages are at an increased risk of breast cancer compared to women who have their first child at younger ages.2-3 For example, women who give birth for the first time after age 35 are 40 percent more likely to get breast cancer than women who have their first child before age 20.4 For women who give birth at older ages, the increase in risk from a first pregnancy never gets fully offset by its long-term protective benefits.2-3
Why does age at first birth matter?
The different effects of age at first childbirth on breast cancer risk may be related to breast cells. During pregnancy, breast cells grow rapidly. If there is any genetic damage in the breast cells, it gets copied as the cells grow. This increased genetic damage in the cells can lead to breast cancer. And, the chance of having such genetic damage goes up with age. This may explain why women who have their first child at a later age have a higher risk of breast cancer than women who have their first child at a younger age.1,3
How does childbearing affect your breast cancer risk?
The more children a woman has given birth to, the lower her risk of breast cancer tends to be. After a first child, each childbirth lowers risk.3 The exact reasons behind this link are unclear at this time.
Women who have never given birth (called nulliparous) have a slightly higher risk of breast cancer compared to women who have had more than one child.3 However, women who give birth only once at age 35 or older have a slightly higher risk compared to nulliparous women. This is because the excess risk of having only one child at an older age never quite goes away.2-3
Whether having children protects equally against estrogen receptor-positive and estrogen receptor-negative (including triple negative) breast cancers is under study.5 Learn more about triple negative breast cancers.
Breastfeeding and breast cancer risk
Breastfeeding lowers the risk of breast cancer and has other health benefits for mothers and infants.6-7 The longer a woman breastfeeds (the combined time of breastfeeding for all children), the greater the protective benefit for breast cancer risk tends to be (learn more).6
Breast cancer during pregnancy
A breast cancer diagnosis during pregnancy is rare. However, when it does happen, it can be safely and successfully treated (learn more).
If you have concerns about changes in your breasts while you are pregnant or breastfeeding, talk to your health care provider.
Pregnancy and breast cancer survival
Having a child after treatment for breast cancer appears to be safe for women.8-11 If you are a survivor and are considering becoming pregnant, talk to your health care provider about the best timing of a pregnancy based on your treatment and cancer.
Pregnancy does not appear to lower a woman’s chances for long-term survival after breast cancer.8-11 In fact, a meta-analysis that combined the results from 14 studies found women who had a child after breast cancer treatment had better overall survival than women who did not have a child after treatment.10
Although having a child after treatment does not have a negative impact on survival, not all women may get a survival benefit. Women who become pregnant after treatment ends may be healthier than those who do not. Thus, the survival benefit found in studies may be due to the fact that only healthier women pursued pregnancy.10 Learn more about findings from studies on pregnancy after breast cancer treatment and survival.
Breast cancer treatment and fertility
Some treatments for breast cancer can impact fertility. Both chemotherapy and tamoxifen can cause menopause or bring on natural menopause earlier than normal (some types of chemotherapy are more likely than others to cause early menopause). Tamoxifen (generally given for five years) can also shorten the window of time to have children.12-14 Taking tamoxifen during pregnancy can harm the fetus, so women should wait until tamoxifen treatment is completed before becoming pregnant.14
If you wish to have a child after breast cancer treatment, talk to your health care provider (and if possible, a fertility specialist) before you begin treatment to discuss your options. Meeting with a fertility specialist as early as possible (before surgery) offers the widest range of options.12
Preserving fertility during breast cancer treatment
There are a few steps you can take before and during treatment to increase your chances of having a child after your breast cancer treatment.
Before breast cancer treatment begins, you may store fertilized embryos. In this procedure, eggs are collected over a number of menstrual cycles, then fertilized and frozen. After treatment, the embryos can be thawed and implanted into the uterus. This procedure has a good rate of success, but it also has some down sides. Treatment may be delayed while eggs are collected, and a sperm donor is needed to fertilize the eggs before they are stored.15-16
Unfertilized eggs (which do not require a sperm donor) can also be frozen and stored. However, this method is much less successful than using fertilized eggs and is still considered experimental.16
Protecting the ovaries during chemotherapy
Chemotherapy attacks fast-growing cells (not only cancer cells but also cells in other parts of the body, like the ovaries). Drugs like goserelin (Zoladex), leuprolide (Lupron) and triptorelin can shut down the ovaries during chemotherapy, which may protect them from damage and lower the chances of early menopause.17 More studies are needed to know whether these drugs affect prognosis.15-16
According to Ann Partridge, MD, MPH, Clinical Director of the Breast Oncology Center at Dana-Farber Cancer Institute and Associate Professor of Medicine at Harvard Medical School “the relationships between breast cancer risks and reproductive health are quite complex and the subject of intensive prior and ongoing research. Continuing to improve our understanding of these relationships is critical to the health and well-being of breast cancer survivors and women at risk for breast cancer. ”
- Having children can lower breast cancer risk, especially for younger women. The more children a woman gives birth to, the lower her risk of breast cancer.
- However, having one child at a later age can slightly increase risk.2-4
- Having a child after breast cancer treatment does not worsen survival.
- Women diagnosed with breast cancer who want to have a child after treatment should talk to a fertility specialist as early as possible, ideally before treatment begins. Even if you choose not to take one of the steps available, exploring all of your options may help you feel more comfortable with your choices later in life.18
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