The safety and efficacy of controlled ovarian hyperstimulation for fertility preservation in women with early breast cancer: a systematic review

Study question: Can controlled ovarian hyperstimulation (COH) for fertility preservation be effectively conducted in women with breast cancer without worsening their prognosis?

Summary answer: COH with co-administration of letrozole suppresses oestradiol levels without significantly impacting oocyte yield or decreasing disease-free survival rates.

What is known already: Oestradiol has the capacity to stimulate the proliferation of breast cancer cells. COH can cause oestradiol levels to rise by an order of magnitude above physiological levels. Concern exists regarding the effect of supra-physiological oestradiol levels in women with a recent diagnosis of breast cancer.

Study design, size, duration: A systematic review of the literature was performed using MEDLINE (PubMed database), EMBASE and the Cochrane Library. The search was restricted to articles written in English. No restrictions regarding the date of publication were applied. Safety was assessed in terms of relapse rates and cancer-related mortality rates. Peak oestradiol concentrations were recorded for different stimulation protocols. Efficacy was measured in terms of the total number of oocytes collected and proportion of mature oocytes. The primary outcome was mortality/recurrence in premenopausal women with Stage I-IIIB breast cancer who underwent COH in the immediate post-operative period, prior to chemotherapy.

Participants/materials, setting, methods: This is a systematic review of randomized control trials (RCTs), case control and cohort studies reporting on the primary outcome of mortality/recurrence after COH in women with early breast cancer, or secondary outcomes of oocyte yield and peak oestrogen concentration. Owing to the small number of RCTs available, other study types were included. The last electronic search was run in April 2016. Two prospective non-randomized studies reported relapse and breast cancer-related mortality rates in 397 women with breast cancer, of whom 149 underwent COH. Twelve studies reported the peak oestradiol concentrations of 882 women undergoing COH with letrozole co-administration. Four studies compared the oocyte yield of 248 women who underwent COH plus letrozole with 254 women who underwent standard COH. Two studies compared peak oestradiol concentrations and oocyte yield in 61 women who underwent COH with tamoxifen co-administration and 49 women who underwent COH without tamoxifen. One study compared letrozole and tamoxifen co-administration, and another study compared the co-administration of letrozole and anastrozole.

Main results and the role of chance: The search identified 1002 records of which 15 were included in the final analysis. There was no evidence of a decline in relapse-free survival rates in the two studies of women with breast cancer who received COH with letrozole co-administration compared with women who did not undergo fertility preservation procedures. The largest of these studies reported recurrences in 6/120 (5.0%) women who received COH plus letrozole compared with 12/217 (5.5%) women who did not undergo COH (mean follow-up 5.0 versus 6.9 years; hazard ratio for recurrence 0.77, 95%CI 0.28-2.13). Conclusions regarding women with breast cancer who received tamoxifen during COH could not be made due to insufficient data. Peak oestradiol concentrations (338-829 pg/ml) were suppressed by letrozole when commenced on Days 2-3, with no decrease in oocyte yield. Tamoxifen does not suppress oestradiol concentrations, but may convey protection via its inhibitory action on the oestrogen receptor.

Limitations, reasons for caution: Any statements regarding the safety of COH in women with breast cancer are based on a limited number of observational studies. High quality evidence is unlikely to become available for ethical and practical reasons. Whilst available data do not indicate a decline in disease-free survival, a small effect cannot be excluded. Breast cancers are heterogeneous in their genetic profile and receptor status, making the results of studies difficult to generalize to individual cases. The implication of alterations in other hormone levels such as androgens, progestins or vascular endothelial growth factor secondary to COH in women with breast cancer has not been quantified.

Wider implications of the findings: The co-administration of 5 mg of letrozole daily commencing on Day 2 and continuing throughout COH is recommended as it reduces peak oestradiol concentrations without significantly decreasing oocyte yield. The use of a GnRH agonist trigger is beneficial as oestradiol concentrations rapidly decrease post-administration and rates of ovarian hyperstimulation are lower than with an hCG trigger, without a corresponding reduction in clinical pregnancy or live birth rates in cryopreservation cycles. The protective effect of tamoxifen has not been evaluated although theoretically may be of benefit due to its action on the oestrogen receptor.

Study funding/competing interest(s): None.

Registration number: None.