Women diagnosed with breast cancer and desiring preservation of fertility via egg or embryo freezing require special consideration because a. its the most common cancer in women and b. its estrogen sensitive. Estrogen increases five to ten folds during conventional ovarian stimulation. Limiting estrogen exposure during stimulation appears to be an important safety consideration. Briefly, breast cancer is treated using surgery followed 4 weeks later by chemotherapy, radiation and other treatments (hormonal treatment e.g. tamoxifen, antibodies e.g. trestazumab..)
To mitigate the rise in estrogen during stimulation, I participated in designing a special method for ovarian stimulation and study its safety. A newer class of medication (aromatase inhobitors) became available (and approved by The US Food & Drug Adminstration). One member of this group (letrozole) is added to conventional medication used for ovarian stimulation. Letrozole decreases the activity of the enzyme that makes estrogen. Estrogen during stimulation remain within a low level, comparable to women’s natural cycles.
When this protocol was tested (by comparing two groups of women; one underwent ovarian stimulation and the other group declined and proceeded directly to cancer treatment), there was no difference in survival or recurrence between the group that underwent ovarian stimulation and those that declined fertility preservation.
Lets Take a Closer Look!
- Both embryo and egg freezing require ovarian stimulation and about 2–3 weeks to accomplish that
- An average woman in this study was followed for about two years. So long term outcomes are not known yet
- After surgery, a woman is given 4 weeks or so for the incision to heal. Studies have shown that a delay of up to 84 days (12 weeks) between surgery and chemotherapy does not affect the outcome
- In expert hands, that protocol yielded an average of 10 embryos or oocytes per patient
- Embryos never get exposed to letrozole as they are frozen and not transferred in the same cycle
- Some physicians use conventional protocols for stimulation with no modification arguing that estrogen exposure in brief (10 to 14 days). It seems prudent though to reduce estrogen exposure during stimulation.
Call to action: Since published work indicates that stimulation of the ovary to freeze eggs or embryos is unlikely to increase breast cancer recurrence, patients and physicians should engage in a candid discussions of risks and benefits of ovarian stimulation for fertility preservation rather than dismissing it altogether on safety grounds in the absence of a clear evidence.