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.   

Storing embryos

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  

Summary

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. ”  

To summarize: 

• 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 

References

1. Lambe M, Hsieh C, Trichopoulos D, Ekbom A, Pavia M, Adami HO. Transient increase in the risk of breast cancer after giving birth. N Engl J Med. 331(1):5-9, 1994. 

2. Colditz GA, Rosner B. Cumulative risk of breast cancer to age 70 years according to risk factor status: data from the Nurses’ Health Study. Am J Epidemiol. 152(10):950-64, 2000. 

3. Willett WC, Tamimi RM, Hankinson SE, Hunter DJ, Colditz GA. Chapter 20: Nongenetic Factors in the Causation of Breast Cancer, in Harris JR, Lippman ME, Morrow M, Osborne CK. Diseases of the Breast, 4th edition, Lippincott Williams & Wilkins, 2010.  

4. Ewertz M, Duffy SW, Adami HO, et al. Age at first birth, parity and risk of breast cancer: a meta-analysis of 8 studies from the Nordic countries. Int J Cancer. 46(4):597-603, 1990.  

5. Shinde SS, Forman MR, Kuerer HM, et al. Higher parity and shorter breastfeeding duration: association with triple-negative phenotype of breast cancer. Cancer. 116(21):4933-43, 2010. 

6. Collaborative Group on Hormonal Factors in Breast Cancer. Breast cancer and breast feeding: collaborative reanalysis of individual data from 47 epidemiological studies in 30 countries, including 50,302 women with breast cancer and 96,973 women without the disease. Lancet 20:187-195, 2002. 

7. Ip S, Chung M, Raman G, et al. Breastfeeding and maternal and infant health outcomes in developed countries. Rockville, MD: US Department of Health and Human Services. http://www.ahrq.gov/downloads/pub/evidence/pdf/brfout/brfout.pdf, 2007. 

8. Mueller BA, Simon MS, Deapen D, et al. Childbearing and survival after breast carcinoma in young women. Cancer. 98(6): 1131-40, 2003.  

9. Kroman N, Jensen MB, Wohlfahrt J, Ejlertsen B. Pregnancy after treatment of breast cancer–a population-based study on behalf of Danish Breast Cancer Cooperative Group. Acta Oncol. 47(4):545-9, 2008. 

10. Azim HA Jr, Santoro L, Pavlidis N, et al. Safety of pregnancy following breast cancer diagnosis: a meta-analysis of 14 studies. Eur J Cancer. 47(1):74-83, 2011.   

11. Valachis A, Tsali L, Pesce LL, et al. Safety of pregnancy after primary breast carcinoma in young women: a meta-analysis to overcome bias of healthy mother effect studies. Obstet Gynecol Surv. 65(12):786-93, 2010. 

12. Lee S, Ozkavukcu S, Heytens E, Moy F, Oktay K. Value of early referral to fertility preservation in young women with breast cancer. J Clin Oncol. 28(31):4683-6, 2010. 

13. Partridge AH and Ginsburg ES. Chapter 96: Reproductive Issues in Breast Cancer Survivors, in Harris JR, Lippman ME, Morrow M, Osborne CK. Diseases of the Breast, 4th edition, Lippincott Williams & Wilkins, 2010.  

14. National Comprehensive Cancer Network. NCCN Clinical practices guidelines in oncology: Breast cancer. V.2.2011. http://www.nccn.org, 2011. 

15. Jeruss JS, Woodruff TK. Preservation of fertility in patients with cancer. N Engl J Med. 360(9):902-11, 2009. 

16. Hulvat MC, Jeruss JS. Fertility preservation options for young women with breast cancer. Curr Opin Obstet Gynecol. 23(3):174-82, 2011. 

17. Lucia Del Mastro, Luca Boni, Andrea Michelotti, et al. Effect of the gonadotropin-releasing hormone analogue triptorelin on the occurrence of chemotherapy-induced early menopause in premenopausal women with breast cancer: a randomized trial. JAMA. 306(3):269-276, 2011. 

18. Letourneau JM, Ebbel EE, Katz PP, et al. Pretreatment fertility counseling and fertility preservation improve quality of life in reproductive age women with cancer. Cancer. 2011 Sep 1 [Epub ahead of print].