Cancer PYNK

Breast cancer and fertility

Woman in headscarf holding baby

My young female patients with breast cancer often ask me about their fertility. In this post, I’ll answer some of the most frequently asked questions.

A woman is born with 1 to 2 million immature eggs in her ovaries. At puberty, the brain begins to send a monthly signal to the ovary to produce a mature egg, which is ready to be fertilized by a sperm. Sperm entering the vagina travel up through the cervix, uterus and fallopian tubes to fertilize the mature egg producing an embryo, the beginning of a baby. The embryo travels through the fallopian tube back to the uterus and the pregnancy continues there. If a sperm does not meet the mature egg, the egg dies and the uterine lining, which has been getting thicker in order to nourish an embryo, sheds resulting in the bleeding of menstruation. The cycle continues monthly, normally interrupted only by pregnancy, until the woman reaches menopause at the average age of 51.

female reprodcutive or

A woman’s fertility (ability to get pregnant) decreases after age 30 and this decrease becomes more rapid after about age 37. The ability to get pregnant naturally generally ends many years before menopause, as early as the mid to late 30’s and generally by age 45.

How can breast cancer treatments affect fertility?

Certain chemotherapy drugs, especially the drug cyclophosphamide, which is part of almost all chemotherapy regimens used after surgery to prevent recurrence, damage the immature eggs in the ovary. The result is that permanent menopause either occurs immediately or occurs at an earlier age than it normally would. Most women will find that their period stops while on chemotherapy and takes several months to return, if it returns at all. Even if her period returns, however, she may no longer be fertile, as her ovaries may not be producing normal, mature eggs. A woman is more likely to go into permanent menopause or become infertile after chemotherapy with a higher total dose of cyclophosphamide and if she is older. It is very unlikely that a woman who receives breast cancer chemotherapy after age 40 will still be fertile. The risk of miscarriage is also higher for women who conceive naturally if they have received chemotherapy in the past.

Hormonal treatments like tamoxifen do not damage the ovaries. However, they indirectly affect fertility because while they are being taken and for at least 3 months after they are stopped, pregnancy is not allowed as tamoxifen can cause serious birth defects. Similarly, pregnancy is not possible while one is getting ovarian suppression injections like Lupron or Zoladex. There is early evidence that it may be safe to interrupt hormonal therapy for up to two years after being on it for a minimum of 18 months in order to have a baby and breast-feed. This is currently being studied in an international breast trial called POSITIVE. Learn more about POSITIVE here.

How can a woman maximize her chances of a future successful pregnancy before starting treatment? What can a woman do before starting chemotherapy or hormone therapy to preserve her fertility?

Embryo freezing after in vitro fertilization (IVF) is the best option for women who have a male partner who can provide sperm or who wish to use a sperm donor. Hormones are given to the woman to artificially stimulate her ovaries to produce many mature eggs. This process takes less than two weeks. The eggs are harvested by inserting an instrument through the vagina. The eggs are then fertilized in the laboratory (a process called in vitro fertilization or IVF) to create several embryos that are frozen in a special very cold freezer. Embryos can be frozen for many years without being damaged. When the woman is ready to become pregnant the embryos are thawed, checked for genetic abnormalities, and one or two are implanted through the vagina into her uterus. The pregnancy success rate is approximately 50% per embryo transferred if the eggs were harvested before age 35 but will be lower if she was older.

If the woman does not have a male partner and does not want to use a sperm donor she can have her unfertilized mature eggs frozen for future use. The eggs can later be thawed and fertilized with donor or male partner sperm (IVF). The success rate per egg is a little lower than for frozen embryos as eggs are more likely to be damaged by freezing and thawing than embryos. In some cases, if not enough eggs are harvested with one cycle of hormonal stimulation, there is time to perform a second cycle.

At the present time for women who are residents of Ontario and have Ontario Health Insurance Plan (OHIP) coverage, the government will cover the cost of one cycle of egg harvesting and embryo freezing. There is partial charitable funding available for women who live in other provinces or who do not qualify for government funding.

Several studies suggest that suppressing the ovaries during chemotherapy with an injection like Lupron or Zoladex partially protects the ovaries from chemotherapy damage. These drugs are expensive but are covered by most private and government drug plans. This is a good option for women who cannot afford egg or embryo freezing or who want to preserve their natural fertility if possible and use IVF only as a back-up, a particularly wise choice if only a few eggs or embryos could be frozen.

Are fertility treatments safe after a diagnosis of breast cancer?

Studies show that in general chemotherapy (and hormone therapy) can be started any time within 3 months of surgery so a two-week delay for harvesting eggs is usually not an issue. For most women who will be getting chemotherapy before surgery such a delay is also totally safe.

About 70% of breast cancers in young women are sensitive to hormones in the body. However, so far studies do not show that the hormones used for ovarian stimulation or ovarian suppression increase the risk of breast cancer recurrence. In fact, in some groups of women (eg. those with tumours insensitive to hormones) ovarian suppression may actually decrease the risk of breast cancer recurrence for reasons that are not understood.

Is it too late to do anything about fertility after breast cancer treatment if natural conception does not occur?

For women who do not choose one of the above options or for whom they are not successful, IVF with donor eggs and a male partner’s sperm can be used. This has a higher success rate than freezing and thawing your own embryos because fresh eggs from a young donor can be used and fertilized. Women without a male partner can use donor embryos.

Is it safe to get pregnant after a diagnosis of breast cancer?

Although for many years physicians believed that pregnancy after a breast cancer diagnosis would/could increase the risk of cancer recurrence, studies consistently show that this is not true. The risk of birth defects in babies of women who had breast cancer is the same or only slightly higher than the risk in the general population. Studies to date also show no increased risk of breast cancer recurrence for women who choose to breastfeed their babies. Whether breastfeeding can safely be continued for more than 6 months must be considered on a case-by-case basis.

Many women don’t know how long they should wait after their breast cancer diagnosis before trying to become pregnant. This decision depends on many factors including age, the likelihood of cancer recurrence, length of hormone treatment, social/partner pressures, family supports, etc. and this should be discussed carefully with one’s oncologist.

Resources for further information

PYNK patient Sonia shares her story about fertility after breast cancer.


About the author

Dr. Ellen Warner

Dr. Ellen Warner is a medical oncologist at Sunnybrook’s Odette Cancer Centre.