Ovarian stimulation, followed by intracytoplasmic sperm injection and cryopreservation of embryos, is currently the most successful procedure for fertility preservation in newly diagnosed cancer patients. Depending on the patient’s age, a survival rate of the embryos following thawing of 35–90%, an implantation rate of up to 30%, and a cumulative pregnancy rate of 30–40% can be achieved [12, 13].
Freezing unfertilized oocytes is also a promising option for preserving fertility today. Oocyte banking does not require any partner or sperm donor and it may also accord better with various religious or ethical considerations than embryo freezing. With recent improvements in freeze–thaw protocols such as vitrification, promising results with more than 60% of mature oocytes surviving after thawing and subsequent fertilization have been reported — rates comparable with fresh oocytes [14, 15].
For either of these methods to be successful, however, appropriate quantities of oocytes have to be obtained. In addition, because the time frame up to the initiation of chemotherapy and/or radiotherapy is limited, usually only one IVF cycle can be carried out, and the numbers of oocytes or embryos cryopreserved are consequently often not sufficient for several transfer attempts. For maximum effectiveness, combinations with other fertility preservation techniques therefore need to be considered.
Cryopreservation of ovarian tissue offers an effective combination. Cryopreservation of ovarian tissue before oncologic treatment has recently become one of the most promising techniques for preserving fertility. It allows storage of a large number of primordial and primary follicles. It can be carried out rapidly at any time in the menstrual cycle without delaying the oncological treatment and provides a unique option for preserving fertility in prepubertal or premenarchal female patients . However, the method is surgically invasive and there is a potential risk that malignant cells in the frozen tissue may lead to recurrence of the primary disease after transplantation. For most conditions, however, the risk is low and is presumably related to the stage of disease at the time of ovarian tissue cryopreservation, although considerable caution is advisable with cryoconserved tissue from patients with leukemia, borderline ovarian tumor, or with a high risk of ovarian metastases (e.g., in adenocarcinoma of the cervix or stage III–IV breast cancer) . A total of 20 live births have been reported to date after orthotopic transplantation of cryopreserved ovarian tissue [18–21]. Although cryopreservation of ovarian tissue is still considered experimental, the technique is now gaining worldwide acceptance.
In the cancer patients included in the present study, ovarian stimulation was carried out first, followed by laparoscopic collection of the ovarian tissue. Although it has been reported that ovarian tissue is of poor quality after ovarian stimulation , no data on this topic have so far been published. Histological examination of the ovarian tissue showed a normal age-related follicle distribution. No histological differences were found from ovarian tissue from patients who underwent ovarian tissue cryopreservation in our department without prior ovarian stimulation. Nor was any correlation noted between the numbers of oocytes retrieved and the follicle distribution in the ovarian tissue. In patients with fewer retrieved oocytes, the numbers of follicles were similar to those in patients with a high response to ovarian stimulation.
The ovarian response to stimulation is crucial for successful fertility preservation, and there has been concern regarding the ovarian response to ovarian stimulation in cancer patients. In the present study, different stimulation protocols were used due to the different starting days for stimulation. Adequate numbers of oocytes were retrieved within 2 weeks. The average number of oocytes retrieved per patient was 10, and 67% of the oocytes were successfully fertilized. This is in accordance with recent studies that have reported no significant changes in the ovarian reserve or response to gonadotropins in patients with various types of cancer [19, 20]. However, other studies have reported a poorer ovarian response in cancer patients undergoing IVF treatment protocols [17, 18]. The published data on this topic are still inconsistent.
The present group of patients included five women with breast cancer, one of whom had estrogen receptor–positive breast cancer. Concerns have been raised regarding the use of controlled ovarian stimulation in patients with hormone-dependent tumors, due to inadequate data on short-term increases in hormonal effects on the tumor. Moreover, as animal models suggest, estrogen may also play a role in stimulating the growth of estrogen receptor–negative breast cancers . Conventional stimulation protocols with gonadotropins are therefore modified to include administration of the aromatase inhibitor letrozole [9, 24] or the selective estrogen modulator tamoxifen . These protocols have been used with success in reducing the estradiol excesses that are normally seen with conventional protocols, and short-term follow-up data for these protocols have not shown any detrimental effects on survival .
The risk of ovarian hyperstimulation syndrome (OHSS) is a known complication of controlled ovarian stimulation. One patient in the present study developed a mild OHSS, but the start of cancer treatment did not have to be postponed in any of the patients. The overall risk of severe OHSS is low, and in cancer patients it is also reduced, given that pregnancy will not occur; however, the risk should not be underestimated. Careful selection of the gonadotropin starting dosage, close monitoring, and step-down dosing are critical for avoiding complications. Triggering using a GnRH agonist alone or together with low-dose hCG might potentially further reduce the risk of hyperstimulation [26, 27].
A potential side effect of the subsequent use of oocyte retrieval and ovarian tissue extraction may be bleeding in the residual ovarian tissue. Stimulated ovaries are more fragile than unstimulated ovarian tissue, which has a more compact structure. Stimulated ovaries have to be handled with greater care in comparison with unstimulated ovaries, to avoid injuries to the surface and to minimize possible tissue damage and bleeding. However, no side effects of this type were observed in any of the patients.
Several attempts have been made to improve the effectiveness of fertility preservation programs by combining different techniques. Removing ovarian tissue first and starting ovarian stimulation approximately 1–2 days later is an effective alternative approach. The partial removal of ovarian tissue does not substantially affect the average number or quality of oocytes retrieved after ovarian stimulation .
The combination of cryopreservation of ovarian tissue before chemotherapy and ovarian stimulation after the start of chemotherapy should no longer be carried out, as the efficacy of IVF is dramatically reduced even after one round of chemotherapy and high rates of malformation of offspring after treatment with alkylating agents have been demonstrated experimentally [28, 29].
If there is no time for ovarian stimulation, cryopreservation of oocytes retrieved during dissection of resected ovarian tissue has also been reported as a potential strategy for preserving fertility in patients with cancer. The combination of in vitro maturation (IVM) with oocyte cryopreservation prevents any delay in cancer treatment and avoids the risks associated with high estradiol levels in hormone-sensitive tumors . Although healthy infants have been born following IVM, implantation and pregnancy rates are generally lower than for IVF with mature oocytes [31, 32].
Administration of GnRH-agonist analogs, in an attempt to reduce the gonadotoxic effects of chemotherapy by simulating a prepubertal hormonal milieu, is another fertility preservation method and should be combined with other fertility-protecting measures as well if possible. Although conclusive proof is still awaited, there is increasing evidence that GnRH agonists are effective in protecting the ovaries . Administration of these agents may be considered on an individual basis, as the method is safe, noninvasive, and easy to administer.