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How Breast Cancer Affects Your Fertility

by Karine Chung, MD, MSCE

At the time of their diagno­sis, many women with breast cancer have not yet started or completed their families. Though the potential for infertility can be a great source of stress, it can get lost in the whirlwind of emotions as a young woman faces her diagnosis.

How does breast cancer therapy affect fertility?
Though the diagnosis of breast cancer itself does not affect 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. However, these treatments may also negatively affect a woman’s ability to conceive.

Chemotherapy, particularly alkylating agents, can quickly and dramatically reduce a woman’s supply of eggs. Since all women are born with a limited quan­tity of eggs, which naturally declines over time until menopause (when the egg supply is essentially depleted), a reduc­tion due to chemotherapy can result in immediate or eventual premature meno­pause in many women. 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 after cancer therapy, pregnancy using one’s own eggs may no longer be possible regardless of whether menstrual cycles are occurring.

In vitro fertilization (IVF) and freezing embryos is the most proven method of fertility preservation.

In contrast, tamoxifen is not known to directly damage the ovaries or affect the egg supply. However, because the duration of treatment is typically five years, many women will experience age-related infertility upon the comple­tion of tamoxifen.

Women generally experience an accelerated decline in fertility around age 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. For women who start tamoxifen after age 35, there is a substantial risk of age-related infertility by the time the five-year course is completed.

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

What are the options for fertility preservation before treatment?
In vitro fertilization (IVF) and freezing embryos is the most proven method of fertility preservation, and 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. Therefore, these methods are most suitable for women who can safely delay cancer treatment for two to six weeks. For women who need to start their chemotherapy imme­diately, ovarian tissue can be removed surgically and frozen for future use.

How do I know whether I am fer­tile after cancer treatment?
Many women will resume regular menstrual periods after treatment. However, 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. An ultrasound of the ovaries can also be useful to approximate fer­tility potential. These tests are best performed and interpreted by a repro­ductive endocrinologist.

What options do I have if I am not fertile after cancer treatment?
For women who are having trouble con­ceiving or who have diminished 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.

What options do I have if preg­nancy is not deemed safe after cancer treatment?
So far, research does not suggest that pregnancy after breast cancer triggers recurrence or decreases survival. However, because of the known association between breast can­cer and hormones like estrogen, which are elevated throughout pregnancy, some breast cancer survivors may be advised to avoid becoming pregnant. For these women, gestational surrogacy is an op­tion. Embryos from the survi­vor are placed into the uterus of another woman who then carries the pregnancy to term in this treatment pro­cess. Adoption is also an option.

If you are considering having chil­dren after cancer, be sure to speak with your oncologist about your fertility questions before beginning treatment. Because the impact of cancer treatment on a woman’s fertility varies from indi­vidual to individual, it is important to understand your specific risks.

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