Does pregnancy affect the risk of other cancers?

Research has shown the following with regard to pregnancy and the risk of other cancers:

  • Women who have had a full-term pregnancy have reduced risks of ovarian27,28 and endometrial29 cancers. Furthermore, the risks of these cancers decline with each additional full-term pregnancy.
  • Pregnancy also plays a role in an extremely rare type of tumor called a gestational trophoblastic tumor. In this type of tumor, which starts in the uterus, cancer cells grow in the tissues that are formed following conception.
  • There is some evidence that pregnancy-related factors may affect the risk of other cancer types, but these relationships have not been as well studied as those for breast and gynecologic cancers. The associations require further study to clarify the exact relationships.

As in the development of breast cancer, exposures to hormones are thought to explain the role of pregnancy in the development of ovarian, endometrial, and other cancers. Changes in the levels of hormones during pregnancy may contribute to the variation in risk of these tumors after pregnancy.30

Does fertility treatment affect the risk of breast or other cancers?

Women who have difficulty becoming pregnant or carrying a pregnancy to term may receive fertility treatment. Such treatment can include surgery (to repair diseased, damaged, or blocked fallopian tubes or to remove uterine fibroids, patches of endometriosis, or adhesions); medications to stimulate ovulation; and assisted reproductive technology.
Ovarian stimulation and some assisted reproductive technologies involve treatments that temporarily change the levels of estrogen and progesterone in a woman’s body. For example, women undergoing in vitro fertilization (IVF) receive multiple rounds of hormone treatment to first suppress ovulation until the developing eggs are ready, then stimulate development of multiple eggs, and finally promote maturation of the eggs. The use of hormones in some fertility treatments has raised concerns about possible increased risks of cancer, particularly cancers that are linked to elevated levels of these hormones.

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Many studies have examined possible associations between use of fertility drugs or IVF and the risks of breast, ovarian, and endometrial cancers. The results of such studies can be hard to interpret because infertility itself is linked to increased risks of these cancers (that is, compared with fertile women, infertile women are at higher risk of these cancers even if they do not use fertility drugs). Also, these cancers are relatively rare and tend to develop years after treatment for infertility, which can make it difficult to link their occurrence to past use of fertility drugs.

Breast cancer: The bulk of the evidence is consistent with no increased risk of breast cancer associated with the use of fertility drugs or IVF.31–34

Ovarian cancer: There is some uncertainty about whether treatment for infertility is a risk factor for ovarian cancer. A 2013 systematic review of 25 studies that included more than 180,000 women found, overall, no strong evidence of an increased risk of invasive ovarian cancer for women treated with fertility drugs.35 In one study, women who underwent IVF had an increase in risk of ovarian borderline malignant tumors.36

Endometrial cancer: Overall, the use of fertility drugs or IVF does not appear to increase the risk of endometrial cancer.34

Selected References

1. Colditz GA, Baer HJ, Tamimi RM. Breast cancer. In: Schottenfeld D, Fraumeni JF, editors. Cancer Epidemiology and Prevention. 3rd ed. New York: Oxford University Press, 2006.

2. Russo J, Moral R, Balogh GA, Mailo D, Russo IH. The protective role of pregnancy in breast cancer. Breast Cancer Research 2005; 7(3):131–142.

3. Britt K, Ashworth A, Smalley M. Pregnancy and the risk of breast cancer. Endocrine-Related Cancer 2007; 14(4):907–933.

4. Bernstein L. Epidemiology of endocrine-related risk factors for breast cancer. Journal of Mammary Gland Biology and Neoplasia 2002; 7(1):3–15.

5. Lord SJ, Bernstein L, Johnson KA, et al. Breast cancer risk and hormone receptor status in older women by parity, age of first birth, and breastfeeding: a case-control study. Cancer Epidemiology, Biomarkers & Prevention 2008; 17(7):1723–1730.

6. Ma H, Bernstein L, Pike MC, Ursin G. Reproductive factors and breast cancer risk according to joint estrogen and progesterone receptor status: a meta-analysis of epidemiological studies. Breast Cancer Research 2006; 8(4):R43.

7. Lambe M, Hsieh CC, Chan HW, et al. Parity, age at first and last birth, and risk of breast cancer: a population-based study in Sweden. Breast Cancer Research and Treatment 1996; 38(3):305–311.

8. Vatten LJ, Romundstad PR, Ødegård RA, et al. Alpha-foetoprotein in umbilical cord in relation to severe pre-eclampsia, birth weight and future breast cancer risk. British Journal of Cancer 2002; 86(5):728–731.

9. Terry MB, Perrin M, Salafia CM, et al. Preeclampsia, pregnancy-related hypertension, and breast cancer risk. American Journal of Epidemiology 2007; 165(9):1007–1014.

10. Nechuta S, Paneth N, Velie EM. Pregnancy characteristics and maternal breast cancer risk: a review of the epidemiologic literature. Cancer Causes and Control2010; 21(7):967–989.

11. Opdahl S, Romundstad PR, Alsaker MD, Vatten LJ. Hypertensive diseases in pregnancy and breast cancer risk. British Journal of Cancer 2012; 107(1):176-182.

12. Tamimi R, Lagiou P, Vatten LJ, et al. Pregnancy hormones, pre-eclampsia, and implications for breast cancer risk in the offspring. Cancer Epidemiology, Biomarkers, and Prevention 2003; 12(7):647–650.

13. Vatten LJ, Romundstad PR, Trichopoulos D, Skjærven R. Pre-eclampsia in pregnancy and subsequent risk for breast cancer. British Journal of Cancer 2002; 87(9):971–973.

14. Collaborative Group on Hormonal Factors in Breast Cancer. Breast cancer and breastfeeding: 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. The Lancet 2002; 360(9328):187–195.

15. Kelsey JL, Gammon MD, John EM. Reproductive factors and breast cancer. Epidemiologic Reviews 1993; 15(1):36–47.

16. Dickson RB, Pestell RG, Lippman ME. Cancer of the breast. In: DeVita VT Jr., Hellman S, Rosenberg SA, editors. Cancer: Principles and Practice of Oncology. Vol. 1 and 2. 7th ed. Philadelphia: Lippincott Williams and Wilkins, 2004.

17. Titus-Ernstoff L, Hatch EE, Hoover RN, et al. Long-term cancer risk in women given diethylstilbestrol (DES) during pregnancy. British Journal of Cancer 2001; 84(1):126–133.

18. Hoover RN, Hyer M, Pfeiffer RM, et al. Adverse health outcomes in women exposed in utero to diethylstilbestrol. New England Journal of Medicine 2011; 365(14):1304-14.

19. Verloop J, van Leeuwen FE, Helmerhorst TJ, van Boven HH, Rookus MA. Cancer risk in DES daughters. Cancer Causes & Control 2010; 21(7):999-1007.

20. Reeves GK, Kan SW, Key T, et al. Breast cancer risk in relation to abortion: results from the EPIC study. International Journal of Cancer 2006; 119(7):1741–1745.

21. Michels KB, Xue F, Colditz GA, Willett WC. Induced and spontaneous abortion and incidence of breast cancer among young women: a prospective cohort study. Archives of Internal Medicine 2007; 167(8):814–820.

22. Beral V, Bull D, Doll R, Peto R, Reeves G. Collaborative Group on Hormonal Factors in Breast Cancer. Breast cancer and abortion: collaborative reanalysis of data from 53 epidemiological studies, including 83,000 women with breast cancer from 16 countries. Lancet 2004; 363(9414):1007–1016.

23. Henderson KD, Sullivan-Halley J, Reynolds P, et al. Incomplete pregnancy is not associated with breast cancer risk: the California Teachers Study. Contraception2008; 77(6):391–396.

24. Lash TL, Fink AK. Null association between pregnancy termination and breast cancer in a registry-based study of parous women. International Journal of Cancer2004; 110(3):443–448.

25. Rosenblatt KA, Gao DL, Ray RM, et al. Induced abortions and the risk of all cancers combined and site-specific cancers in Shanghai. Cancer Causes and Control 2006; 17(10):1275–1280.

26. Committee on Gynecologic Practice. ACOG Committee Opinion No. 434: induced abortion and breast cancer risk. Obstetrics and Gynecology 2009; 113(6):1417–1418.

27. Hankinson SE, Colditz GA, Hunter DJ, et al. A prospective study of reproductive factors and risk of epithelial ovarian cancer. Cancer 1995; 76(2):284–290.

28. La Vecchia C, Negri E, Franceschi S, Parazzini F. Long-term impact of reproductive factors on cancer risk. International Journal of Cancer 1993; 53(2):215–219.

29. Titus-Ernstoff L, Perez K, Cramer DW, et al. Menstrual and reproductive factors in relation to ovarian cancer risk. British Journal of Cancer 2001; 84(5):714–721.

30. Persson I. Estrogens in the causation of breast, endometrial and ovarian cancers―evidence and hypotheses from epidemiological findings. Journal of Steroid Biochemistry and Molecular Biology 2000; 74(5):357–364.

31. van den Belt-Dusebout AW, Spaan M, Lambalk CB, et al. Ovarian stimulation for in vitro fertilization and long-term risk of breast cancer. JAMA 2016; 316(3):300-312.

32. Gennari A, Costa M, Puntoni M, et al. Breast cancer incidence after hormonal treatments for infertility: systematic review and meta-analysis of population-based studies. Breast Cancer Research and Treatment 2015; 150(2):405-413.

33. Brinton LA, Scoccia B, Moghissi KS, et al. Long-term relationship of ovulation-stimulating drugs to breast cancer risk. Cancer Epidemiology, Biomarkers & Prevention 2014; 23(4):584-593.

34. Practice Committee of the American Society for Reproductive Medicine. Fertility drugs and cancer: a guideline. Fertility and Sterility 2016; First published online: August 26, 2016. doi: 10.1016/j.fertnstert.2016.08.035

35. Rizzuto I, Behrens RF, Smith LA. Risk of ovarian cancer in women treated with ovarian stimulating drugs for infertility. Cochrane Database of Systematic Reviews 2013; (8):CD008215.

36. Van Leeuwen FE, Klip H, Mooij TM, et al. Risk of borderline and invasive ovarian tumours after ovarian stimulation for in vitro fertilization in a large Dutch cohort. Human Reproduction 2011; 26(12):3456–3465.

Source: National Cancer Insititute.