Frequently Asked Questions About Fertility and Breast Cancer

Women's Health

by Dr. C.H. Weaver M.D. updated 8/2020

Breast cancer is the number one cause of cancer in women of reproductive age. At the time of their diagnosis, many women have not yet started or completed their families. Questions about how cancer and treatment affect the ability to get pregnant in the future often arise as these women face their diagnosis and begin cancer treatment. Some of the common questions and answers are discussed here.

Q: How does breast cancer therapy affect fertility?

Though the diagnosis of breast cancer itself is not believed to have an impact on a woman’s fertility, certain treatments for breast cancer do. Two common components of breast cancer treatment—chemotherapy and tamoxifen—are very effective in decreasing recurrences and improving survival, but these treatments may also negatively affect a woman’s future ability to conceive.

It is known that chemotherapy, especially medications called alkylating agents (such as Cytoxan® [cyclophosphamide]), can immediately and dramatically reduce a woman’s supply of eggs. Because all women are born with a limited quantity of eggs, which naturally declines over the years until menopause (when the egg supply is essentially depleted), a reduction due to chemotherapy can result in premature menopause in 15 to 89 percent of patients. Premature menopause can happen right away or may come a few years after a woman finishes treatment. Even in women who resume regular menstrual periods after treatment, there may be a shortened window of time to achieve pregnancy. If the remaining pool of eggs is already below a critical threshold immediately following cancer therapy, pregnancy using one’s own eggs may no longer be possible regardless of whether menstrual cycles are occurring.

Unlike chemotherapy, tamoxifen is not known to directly damage the ovaries or affect the egg supply. Because the duration of treatment is typically five years, however, many women will experience age-related infertility by the time they complete their tamoxifen. Throughout a woman’s reproductive years, there is a gradual and natural reduction in the number of eggs and a corresponding decrease in the quality of eggs. Women generally experience an accelerated decline in fertility at an average age of 37. Within a matter of years, a critical threshold is reached at which the number and the quality of eggs are too low to result in a successful pregnancy. Thus cessation of fertility naturally occurs at an average age of 41 to 45, though menstrual cycles continue to be regular until about age 46 to 50. For women who start tamoxifen after the age of 35, there is a substantial risk of age-related infertility by the time they complete a five-year course.

Because it is difficult to predict whether a woman will be fertile after cancer treatment, it is a good idea to consider fertility preservation options before starting treatment for those who would like to have children in the future.

Q: What are the options for fertility preservation before treatment?

In vitro fertilization and freezing embryos (fertilized eggs) is the most proven method of fertility preservation; it is the ideal option for women who are married, have a male partner, or are interested in using donor sperm. Women who are single and are not interested in using donor sperm can consider freezing eggs. Whether freezing eggs or embryos, the process starts with the beginning of a menstrual period and takes about two weeks to complete. For that reason these methods are most suitable for women who can safely delay cancer treatment for two to six weeks. For women who need to start chemotherapy immediately, ovarian tissue can be removed surgically and frozen for future use.

Q: How do I know whether I am fertile after cancer treatment?

Many women will resume regular menstrual periods after treatment, but this does not necessarily mean that they are fertile. The most reliable way to assess fertility after cancer therapy is by measuring hormone levels in the blood (follicle-stimulating hormone, estradiol and progesterone levels timed to specific phases of the menstrual cycle, and anti-Müllerian hormone levels). An ultrasound of the ovaries can also be useful to approximate fertility potential. These tests are best performed and interpreted by reproductive endocrinologists.

Q: What are the options if I am not fertile after cancer treatment?

For women who are having trouble conceiving or are determined to have reduced fertility after cancer treatment, standard methods of infertility treatment such as in vitro fertilization can often help. For women who are menopausal after cancer treatment, donor eggs can be used and are very successful in achieving pregnancy.

Q: What are the options if carrying a pregnancy is not felt to be safe after cancer treatment?

So far research does not suggest that pregnancy after breast cancer triggers recurrence or decreases survival. Because of the known association between breast cancer and hormones like estrogen, which are elevated throughout pregnancy, however, some breast cancer survivors may be advised to avoid becoming pregnant. In those women for whom carrying a pregnancy is not felt to be safe, “gestational surrogacy” is an option. This refers to a treatment process in which embryos from the survivor are placed into the uterus of another woman—the gestational surrogate—who then carries the pregnancy to term. Adoption is also an excellent option.

If you are considering having children after completing cancer treatment, be sure to speak with your oncologist about your fertility questions. Because the impact of breast cancer treatment on a woman’s fertility varies from individual to individual, it is important to understand the risks that are specific to you. For many women, consulting a fertility specialist and/or undergoing a fertility preservation procedure prior to the initiation of cancer treatment is worthwhile.


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