Utilization and fertility preservation outcomes in women undergoing embryo cryopreservation before breast cancer treatment: a meta-analysis

Abstract

Purpose:

To assess fertility preservation (the proportion of women who had at least one live birth) and utilization rates (the proportion of women who utilized their cryopreserved embryos) rates among women who cryopreserved their embryos before breast cancer treatments.

Methods:

PubMed and Cochrane library database were searched until December 2024. We included all studies that reported pregnancy outcomes, the number of women who returned for frozen embryo transfer, and the number of women who preserved their fertility. The primary outcome measures were the utilization and fertility preservation rates. Secondary outcome measures were implantation, clinical pregnancy, and live birth rates.

Results:

Of the 12 studies, 9 met the criteria, encompassing >2126 women with breast cancer who cryopreserved their embryos for fertility preservation. In 9 studies that reported the total number of attempts, 424 women underwent 863 embryo transfers. Based on those studies, the clinical pregnancy and live birth rates were 50% (95% CI: 35–65, I²: 80%) and 33% (95% CI: 22–46, I²: 76%), respectively. The utilization and fertility preservation rates were 18% (95% CI: 9–32, I²: 95%) and 39% (95% CI: 29–51, I²: 48%), respectively, all from random-effects models.

Conclusion:

Fertility preservation success with embryos cryopreserved before breast cancer treatments seems to be promising. However, the utilization rate of cryopreserved embryos is low. Additional studies with larger sample size and longer follow up are required to evaluate the long-term utility rates.

Introduction

Breast cancer is the most common malignancy in women, with about 10–15% cases being diagnosed in women of reproductive age [1]. Early detection of breast cancer with routine use of mammography screening and advanced treatment strategies have significantly reduced mortality rates [2]. However, as women with breast cancer become long-term survivors, adverse effects of chemotherapy on ovarian function and fertility become increasingly more impactful on their quality of life. For women with estrogen receptor (ER)-positive tumors, up to 10 years of adjuvant endocrine treatment is recommended [3]. During this period, conception is inadvisable due to the teratogenic potential of these medications [4]. This delay also leads to age-related decline in ovarian reserve and compound chemotherapy-induced follicle losses. Therefore, it is crucial to discuss fertility preservation (FP) options prior to starting chemotherapy and help guide women in methods of FP.

Embryo cryopreservation is an established FP method that requires ovarian stimulation for about two weeks. The safety and feasibility of this technique have been well-studied in infertility patients, enhancing its acceptance and utility [5]. Since breast cancer is a hormone dependent cancer, higher estrogen levels during ovarian stimulation may cause tumor proliferation and metastasis. To protect these patients from the potential deleterious effects of increased estrogen levels, we developed an ovarian stimulation protocol that uses letrozole in combination with follicle-stimulating hormone for the purpose of FP by embryo cryopreservation and reported similar numbers of embryos obtained when compared with conventional ovarian stimulation protocols [6]. Furthermore, there was no significant increase in short-term and long-term recurrence risk [7,8]. In a 2015 prospective report, we showed that embryo cryopreservation after ovarian stimulation preserves fertility in 51% of women with breast cancer and results in pregnancy rates comparable to those in a non-cancer population undergoing in vitro fertilization [9]. Since then, several smaller studies from various countries have explored pregnancy outcomes in women with breast cancer using cryopreserved embryos [10–17]. However, the knowledge on clinical utility and long-term clinical effectiveness of FP by embryo cryopreservation remains limited in women with breast cancer.

We therefore conducted a meta-analysis assessing utilization fertility preservation rates, and pregnancy outcome among women who underwent embryo cryopreservation for FP before breast cancer.

Materials and Methods

The meta-analysis was conducted following the Preferred Reporting Item for Systematic Reviews and Meta-analysis (PRISMA) statement (Figure 1), using a registered protocol (PROSPERO CRD42025641003). The study protocol was approved by the institutional review board of Koc University, Istanbul, Turkey.

Figure 1.

Study selection and inclusion process for the meta-analysis

Search Strategy

We searched the published articles in PubMed and Cochrane library database. The following MESH search headings were used in three different concepts: 1. “Breast cancer*” OR “cancer*” AND “carcinoma*” AND “malignant tumour*” AND; 2. “Embryo*” OR “Embryo cryopreservation*”, “embryo transfer*” OR “frozen embryo transfer*” AND “pregnancy*” OR “live birth*”AND; 3. Fertility preservation*” OR “ovarian stimulation*” AND “controlled ovarian stimulation*” AND “controlled ovarian hyperstimulation*. We did not include abstracts or conference proceedings because the data are usually difficult to assess. The search was limited to full-length manuscripts published in English in peer-reviewed journals up to December 2024. Data were extracted by two reviewers independently (V.T. and O.O.) These authors tried to reach consensus. When there is a disagreement, the third reviewer’s judgement would be sought for (K.O.). But we did not have any disagreement.

Study Selection and Data Extraction

Study quality was evaluated through Joanna Briggs Institute appraisal tools for prevalence studies where possible (Supplemental Table 1). We included all studies that reported pregnancy outcomes, the number of women who returned for frozen embryo transfer, and the number of women who preserved their fertility.

All articles were reviewed and the following data recorded: year of publication, study design, age at embryo cryopreservation, stage of breast cancer, aromatase inhibitor use during ovarian stimulation, mean time from embryo cryopreservation to embryo transfer, the number of women who underwent FP, the number of women who returned for embryo implantation, implantation rate, pregnancy rate, live birth rare, and fetal outcomes. Studies were excluded if they lacked information on pregnancy outcomes and if the pregnancy was achieved after oocyte cryopreservation. We only included studies about embryo cryopreservation, not oocyte cryopreservation.

Outcome Measures

The main question of interest was the utilization (return) and fertility preservation rates (the proportion of women who preserved their fertility). Our secondary aim was to assess implantation, clinical pregnancy and live birth rates. The implantation rate was defined as the percentage of embryos that successfully implanted among those transferred. Clinical pregnancy was defined as the presence of at least one gestational sac during the first ultrasound examination by the eighth week of gestation. Ongoing pregnancies were included in the clinical pregnancy data regardless of the gestational pregnancy age [15]. We previously defined the FP rate as the percentage of women who were able to have at least one live birth among all who attempted a frozen embryo transfer after FP by embryo cryopreservation [9]. The utilization rate (return rate) was defined as the percentage of women who returned and had at least one frozen embryo transferred.

Statistical Analysis

We used descriptive statistics (as reported from original publications or we summarize) in study overview. For meta-analyses, we used the method for a single proportion. For confidence intervals (CIs), we used Clopper-Pearson (‘exact’ binomial) interval, while logit transformation was used for summary measure. For pooling, inverse-variance-weighting was employed, where restricted maximum likelihood estimator was used for estimating τ², which is the variance of the effect sizes across studies, and I² is the fraction of variance that is due to heterogeneity. We report fixed-effect and random-effect estimates together in forest plots to inform readers properly about contribution of each study and potential attenuation in the contributions of large studies. Statistical analyses were carried out using R 4.1.0 (R Core Team, 2021) using meta-analysis package for a single proportion.

Results

Literature Search

Of the 112 articles identified initially, 37 were found to be relevant and were evaluated for eligibility. Twenty-eight studies were excluded because they did not have pregnancy outcomes in women with breast cancer or had pregnancy outcomes only for other cancer types. In the end, nine studies that included a total of 424 women with breast cancer who underwent 863 embryo transfer were analyzed (Figure 1). Of note, we could not account for clustering in our analyses due to unavailability of individual participant data.

Study Characteristics

Other than two prospective and one cross-sectional study [9,13,15], all included studies were retrospective in design. In three of the nine studies, breast cancer stage was reported and the majority of patients who cryopreserved embryos for fertility preservation had a stage ≤3 tumor [9,11,17]. Four studies used aromatase inhibitors along with gonadotropins during ovarian stimulation regardless of estrogen receptor status while two studies used aromatase inhibitors only in women with estrogen receptor positive [15,16]. Two studies did not specify ovarian stimulation protocols [11,14]. Characteristics of the included studies are summarized in Table 1. The time period from embryo cryopreservation to embryo transfer varied from two years to nine years among studies and it was not specified in three studies.

Table 1.

Characteristics of studies on women with breast cancer who underwent embryo transfer after embryo cryopreservation for fertility preservation included in meta-analysis

Author, year of publication, country	Study design	Age at EC (years)	Tumor Stage	Mean time from EC to ET	# of women who underwent EC (n)	# of women who underwent ET (n)	Fertility preservation rate % (n)	Fetal outcome
Oktay, 2015, USA (9)	Prospective cohort	35.8 ± 4.a	Stage≤3	5.25 years (range, 2 to 8.2 years) after oocyte retrieval.	131	33	51.5 (17/33)	No fetal anomalies or malformations (n=25)
Dolmans, 2015, Belgium (10)	Retrospective cohort	34, 34, 41 b	NS	NS	12	3	66.6 (2/3)	NS
Chien, 2017, USA (11)	Retrospective cohort	(25–42) c	Stage 2 and 3	74 months	20	6	33.3 (2/6)	NS
Alvarez, 2018, UK (12)	Retrospective cohort	(30–37) c	NS	10–53 months	145	5	40.0 (2/5)	Term healthy babies (n=3)
Vriens, 2020, Netherlands (13)	Prospective cohort	(23–40) c	NS	at least 2 years after the diagnosis	25	3	66.6 (2/3)	Eleven babies were healthy, one had a congenital anomaly (M. Hirschsprung)
Duraes, 2022, France (14)	Retrospective cohort	(18–40) c,	NS	2–9 years	1650	70	18.5 (13/70)	NS
Okutsu-Horage, 2022, Japan (16)	Retrospective cohort	(30–44) c	NS	3.0 years (range, 0.8–4.6 years)	126	17	47.0 (8/17)	No fetal abnormalities or malformations (n=8)
Takae, 2024, Japan (15)	Cross sectional study	36.7 ± 3.6 a	NS	NS	NS	278	37.9 (123/278)	NS
Chen, 2024, Taiwan (17)	Retrospective cohort	34.3 ± 3.1 a	Stage≤3	NS	17	9	44.4 (4/9)	NS

^aMean and standard deviation

^bAge of three women

^cRange

Abbreviations: EC, Embryo cryopreservation; ET, embryo transfer; NS, not specified

Pregnancy Outcome

In nine pooled studies, >2126 women (in one study the total number of women who cryopreserved embryos was not reported) [15] with breast cancer cryopreserved their embryos for FP. Among women who underwent embryo cryopreservation, 424 later returned for 863 embryo transfers. Although not specified in all studies, some women used a gestational carrier [9]. The clinical pregnancy rate and live birth rate per embryo transfer were 50% (95% CI: 35–65, I²: 80%, random-effect) and 33% (95% CI: 22–46, I²: 76%, random-effect), respectively (Figure 2). The study by Takae et al. [15] had the largest sample size and there were 47 ongoing pregnancies at the time of survey; the contribution of their study is substantially attenuated in the pooled random-effect estimate, compared to the fixed-effect counterpart.

Figure 2.

Implantation rate (A), clinical pregnancy rate (B) and live birth rate (C) in women with breast cancer who cryopreserved their embryos for fertility preservation before treatment and underwent embryo transfer.

Utilization rate (Return rate)

Since one study did not report the total number of women who cryopreserved embryos before breast cancer treatments [15], we pooled 8 studies from 2126 women and the return rate was estimated to be 18% (95% CI: 9–32, I²: 95%, random-effect). This indicates a high heterogeneity among studies (Figure 3).

Figure 3.

Fertility preservation (A) and utilization rates (B) in women with breast cancer

Fertility preservation rate

All ten studies included in the meta-analysis were qualified for this analysis. Based on that pool, the fertility preservation rate was 39% (95% CI: 29–51, I²: 48%, random-effect). Heterogeneity, measured by I², was greatly reduced, making random-effect and fixed-effect estimates (39 vs. 37%) similar (Figure 3).

Fetal outcome

Fetal outcomes were reported in four studies [9,12,13,16]. All babies (n = 47) were healthy without any fetal abnormalities or malformations other than one who had Hirschsprung disease [13]. One study used aromatase inhibitors only in women who had with estrogen receptor-positive tumors, while other studies used aromatase inhibitors in conjunction with gonadotropins regardless of the receptor status. Three women whose embryos were frozen after an ovarian stimulation protocol without an aromatase inhibitor gave birth to one baby each [16].

Discussion

Limited data exist on the success and utility of cryopreserved embryos for FP in women with breast cancer, and most studies had small sample sizes. To address this gap, we conducted a meta-analysis on this topic. We found clinical pregnancy and live birth rates of 50% and 33%, respectively, while only 18% of women returned to utilize their cryopreserved embryos after a follow up of at least 2 years to 9 years. The pregnancy outcomes were comparable to those reported elsewhere in infertility patients undergoing standard in vitro fertilization protocols [18,19] These findings support the efficiency of FP by embryo freezing in women with breast cancer, though nearly 80% of those who cryopreserved embryos have not returned according to these reports.

Embryo cryopreservation was the first technique developed for preserving female fertility and requires an approximately two-week-long ovarian stimulation [20]. However, since most breast malignancies are estrogen-sensitive, elevated estrogen levels during ovarian stimulation may promote tumor proliferation and metastasis. To mitigate this concern, we developed an ovarian stimulation protocol combining letrozole (an aromatase inhibitor) with recombinant follicle-stimulating hormone injections for FP through embryo or oocyte cryopreservation [6]. This protocol yielded similar numbers of oocytes and embryos compared to conventional ovarian stimulation protocols, with no change in short-term or long-term breast cancer recurrence risks [7,8].

While preserving fertility by embryo cryopreservation, one concern is whether pregnancy after breast cancer survival increases recurrence risk. A systematic review of 2,669 women with breast cancer found no significant impact of pregnancy on disease-free survival in ER-positive patients over a 5–10-year follow-up period [21]. Similarly, a study on BRCA carriers, including 4,732 participants, reported no significant difference in disease-free survival between women who became pregnant (n = 659) and those who did not (n = 4,073) after a median follow-up of 7.8 years [22].

Data on the timing of ovarian stimulation in breast cancer patients are limited. However, early reports indicate that random-start ovarian stimulation produces outcomes comparable to standard-start stimulation, including age-appropriate euploidy rates [23–25]. Although pregnancy data from cancer patients undergoing random-start stimulation are sparse, studies in infertile populations show similar clinical and ongoing pregnancy rates between random-start and standard-start protocols [26]. Additionally, some studies suggest that frozen embryo transfer may not be as efficient as the fresh transfer, and current evidence indicates similar success rates between frozen and fresh embryo transfers [27,28].

Though a growing number of women preserve their fertility by embryo cryopreservation, the utilization rate of cryopreserved embryos appears to be low. In our meta-analysis, only 18% of women who underwent ovarian stimulation returned for embryo transfer. The most important factors affecting the return rate are the duration of endocrine therapy and the recurrence of breast cancer. In addition, short follow-up periods, relationship breakdowns, mortality, or concerns about cancer recurrence are the other factors affecting the return rate. Some women may also conceive spontaneously, reducing the need for frozen embryos [29,30]. Future longer-term studies will be needed to determine the long-term utility rates and the reasons for non-utilization.

The strength of our meta-analysis is that, to our knowledge, it is the first meta-analysis to focus exclusively on breast cancer patients, reporting pregnancy outcomes, embryo utilization rates, and the proportion of women who preserved their fertility. Previous meta-analyses included all cancer types, resulting in high heterogeneity due to variations in treatment protocols and patient characteristics [31,32]. Our study also had some limitations. First, endometrial preparation protocols for frozen embryo transfer and the stage of embryos transferred were not reported in most studies. Second, many included studies had small sample sizes and short follow-up periods, which is significant given that ER-positive patients delay pregnancy attempts for up to 10 years due to adjuvant endocrine therapy [3]. Third, data on pregnancy outcomes in women with pathogenic BRCA variants after embryo cryopreservation for FP remain limited, necessitating further research. The FP success and utility rates among women with pathogenic BRCA variants can be different than those without these variants, given that they may already have lower ovarian reserve [33–35], be more liable to chemotherapy induced ovarian reserve loss [36], intervening risk-reducing salpingo-oophorectomy, and the concerns about transmitting the pathogenic variant to their offspring [37,38]. Finally, we believe heterogeneity is due to differences in the design of included studies, variability in patient populations, differences in follow up durations and small sample sizes. We could not retrieve reliable data on important covariates or confounders in a standardized format (e.g., age, comorbidity or practice pattern) or conduct meaningful subgroup analyses as the total number of studies is small. We hope future meta-analysis will allow meta-regression, subgroup analyses, comparisons or use of individual participant data, which could provide more insights into causes of heterogeneity. This study is a meta-analysis of observational studies, not randomized controlled trials. Also, a single study contributes the largest weight to the pooled estimate due to the largest sample size. Yet, our reporting of random-effect estimates as a primary approach may mitigate these issues in some degrees.

In conclusion, the success of fertility preservation through embryo cryopreservation in women with breast cancer is reassuring. Establishing an international registry could help evaluate long-term utilization, pregnancy and offspring outcomes.

Highlights.

• Breast cancer is the most common malignancy in women, with about 10–15% cases being diagnosed in women of reproductive age.

• The knowledge on clinical utility and long-term clinical effectiveness of fertility preservation by embryo cryopreservation remains limited in women with breast cancer.

• The success of fertility preservation through embryo cryopreservation in women with breast cancer is reassuring.

• Though a growing number of women with breast cancer preserve their fertility by embryo cryopreservation, the utilization rate of cryopreserved embryos appears to be low.