OVARIAN STIMULATION IN ONCOLOGICAL PATIENTS
Oocyte cryopreservation represents an important strategy for cancer patients, in countries such as Italy, where embryo cryopreservation is forbidden, but also for those patients who for ethical-religious reasons do not accept freezing of embryos. This technique also presents the advantage of not requiring the presence of a partner at the time of treatment.
The protocol for oocyte banking is similar to an in vitro fertilization: patients undergo to controlled ovarian stimulation (COS) using daily gonadotropin injection in order to promote multifollicular growth and to obtain a large cohort of oocytes to be freeze. The patients referred for fertility preservation due to a malignant disease do not represent the typical population of subfertile women treated in IVF centres. They undergo usually one single COS cycle before starting their oncological treatment. Nowadays, different ovarian stimulation protocols are available to adapt treatment to best suit the cancer patient.
The choice of the right therapy must be individualized in each case depending on patient’s age, type and stage of the cancer, therapeutic plan to be followed, foreseeable
long-term effects, possibility or impossibility of delaying the start of treatment, biology of the tumour and potential for metastasis in the ovary.
4.1 CANCER PATIENTS’ RESPONSE TO OVARIAN STIMULATION
The number of oocytes retrieved and their quality are imperative factors predicting the potential efficacy of the fertility preservation procedure. Consequently, information regarding the expected ovarian performance after controlled ovarian hyperstimulation (COH) is crucial when consulting with the patient.
The existence of a malignant disease may have a negative effect on reproductive system: the increased metabolic state, malnutrition and increased stress hormone levels associated with malignant disease, can affect the hypothalamic-pituitary-gonad axis and reduce fertility (52). Moreover, it has been suggested a possible negative association between the presence of neoplastic disease and ovarian reserve or oocytes quality (53).
A recent meta-analysis, conducted on seven retrospective studies, shows that the number of total oocytes and mature oocyte obtained in cancer patients, who perform ovarian stimulation protocol for fertility preservation, are lower compared to healthy patients (respectively 11.7 ± 7.5 vs. 13, 5 ± 8.4, and 9.0 ± 6.5 vs. 10.8 ± 6.8). In addition, a relative risk of poor response, resulting in cancellation of the cycle, is higher in those patients compared control group (HR 1.32, 95% CI 0.78 to 2.17), although the observed difference is statistical significant, probably due to small size of groups (54).
Recently, Oktay (55) affirms that all women with breast cancer carrier of BRCA1 mutation, have, more frequently a poor response to ovarian stimulation compared to patients without this kind of mutation (33.3% vs. 3.3%). This indicates a possible role of
BRCA1 as an important factor responsible for the impairment in double strand DNA break repair and women’s infertility. In particular, patients with BRCA mutations, who require higher doses of gonadotrophins to achieve multifollicular growth, exhibit BRCA-1 mutations, while this phenomenon is not present in those for a BRCA mutation type -2 (55).
Cancer patients show a diminished ovarian reserve, assessed by AMH serum levels and AFC ultrasound examination, even before any oncologic treatment (56). This phenomenon can be explained by an accelerated follicles loss or a defect in antral follicles recruitment.
4.2 OVARIAN STIMULATION PROTOCOLS
4.2.1 Conventional controlled ovarian stimulation
The choice of the specific stimulation protocol is generally influenced by the time available before starting radiotherapy or chemotherapy. Although multiple different COS protocols are used, the majority of patients are treated with a GnRH antagonist–based protocol, which likely allows the shortest deferral of the initiation of radio/chemotherapy.
Traditional ovarian preparation for IVF requires 9–14 days of ovarian stimulation with exogenous gonadotropins, preceded by ovarian suppression with GnRH agonists for 2 weeks to prevent premature ovulation. Because GnRH agonist is initiated in the luteal phase of the cycle, this may add up to 3 additional weeks to the process, depending on when the patient presents for treatment.
The development of GnRH antagonists has significantly decreased the interval from patient presentation to embryo/oocyte cryopreservation (57). In contrast to GnRH agonists, GnRH antagonists immediately suppress pituitary release of FSH and LH. Their
administration is started to prevent premature LH surge when the size of the lead follicle reaches 12–14 mm at approximately day 6 of gonadotropin stimulation which begins on day 2–3 of a menstrual cycle. This approach still requires awaiting menses before initiating gonadotrophins, but it decreases the interval until oocyte retrieval.
The use of GnRH antagonists during the preceding luteal phase is explored as a method to improve ovarian stimulation by inducing corpus luteum breakdown and synchronizing the development of the next wave of follicles (58). For cancer patients, the idea of administering GnRH antagonists in the luteal phase was driven more by minimizing potential delays for cancer treatment. If a GnRH antagonist (e.g., single dose of 3mg cetrorelix subcutaneously) is given during the midluteal phase, menses ensues a few days later. As a result, ovarian stimulation would be initiated more quickly and a GnRH antagonist would be restarted to prevent LH surge.
4.2.2 “Random-start” controlled ovarian stimulation
Ovarian stimulation for oocyte freezing is started in the early follicular phase with the idea that this optimizes clinical outcomes. Patients owing to the urgency of the cancer treatment and not desirable to wait for the next menstrual period to start stimulation, a random-start stimulation protocol is proposed.
In a small prospective multicenter study, a novel protocol for cancer patients that initiated ovarian stimulation during the luteal phase of the menstrual cycle is described (59). Cancer patients in the luteal phase start GnRH antagonists to down-regulate LH and initiate luteolysis. Simultaneously, follicular stimulation is initiated with recombinant FSH only. Compared with cancer patients stimulated during the follicular phase with either a short
‘‘flare-up’’ protocol or an antagonist protocol, the luteal-phase group had similar number of aspirated oocytes, number of MII oocytes, and fertilization rate.
4.2. 3 Controlled ovarian stimulation&breast cancer
Ovarian stimulation with gonadotropins may induce a potential risk of supraphysiologic estradiol (E2) levels (60). The rise in E2 is directly proportional to the number of follicles recruited to grow; alternative and potentially safer protocols have been introduced for fertility preservation for estrogen-sensitive cancer patients, such as breast cancer and endometrial cancer, including natural-cycle IVF (without ovarian stimulation), stimulation protocols with tamoxifen alone or combined with gonadotropins, and stimulation protocols with aromatase inhibitors to reduce the estrogen production (44).
Natural-cycle IVF gives only one or two oocytes or per cycle and has a high rate of cycle cancellation, so this technique is not recommended especially when the cancer therapy is imminent and the patient does not have the possibility of a second attempt.
Tamoxifen, besides its well-known antagonist effect in estrogen receptors (ER) in the breast, has also an antagonist action in the central nervous system similar to that of clomiphene when binding to ER. The selective antagonist action of clomiphene and tamoxifen in the brain has a direct action in the hypothalamic/pituitary axis by interfering with the negative feed-back of the estrogen-signaling pathway, leads to an increase in gonadotrophin releasing hormone (GnRH) secretion from the hypothalamus and a subsequent release of FSH from the pituitary promoting follicular development, followed by LH surge and ovulation. Studies show that tamoxifen is effective in inducing ovulation as clomiphene (61). Tamoxifen can be used for controlled ovarian stimulation alone,
starting in the 2nd-5th day of the ovarian cycle in doses of 20-60 mg / day, or in combination with gonadotropins (44). The use of tamoxifen for fertility preservation in cancer patients was shown to increase the mature oocyte and embryo yield compared with natural-cycle IVF (1.6 vs. 0.7 and 1.6 vs. 0.6, respectively) and reduce cycle cancellations (62).
Aromatase is a cytochrome P450 enzyme complex that catalyzes the conversion of androstenedione and testosterone to their respective estrogenic products estrone and E2. Aromatase inhibitors, such as letrozole, markedly suppress plasma estrogen levels by competitively inhibiting the activity of the aromatase enzyme (63). In patients with estrogen-sensitive cancers, the main advantage of adding daily letrozole to gonadotropins in ovarian stimulation protocols is to decrease serum E2 levels to be closer to that observed in natural cycles (i.e., E2 <500 pg/mL) without affecting oocyte or embryo yield (64). Stimulation protocols using letrozole alongside with gonadotropins are currently preferred over tamoxifen protocols as treatment with letrozole results in a higher number of oocytes obtained and fertilized when compared to tamoxifen protocols. In a study comparing the efficacy of the letrozole plus gonadotropin protocol in breast cancer patients and the standard IVF protocol in age-matched non-cancer patients with tubal-factor infertility, the breast cancer patients start to receive letrozole (5 mg/d) on menstrual cycle day 2 or 3. Recombinant FSH is added 2 days later and all medications are discontinued on the day of hCG trigger. Letrozole is reinitiated after oocyte retrieval and continued until E2 levels fell to <50 pg/mL (64). This results in similar number of total oocytes retrieved and length of ovarian stimulation compared with standard IVF protocol. Peak E2 levels are significantly lower in the breast cancer patients receiving letrozole compared with the standard standard
stimulation (483 +/- 278.9 pg/mL vs. 1464.6 +/- 644.9 pg/mL). Studies, evaluated the effect of letrozole on the maturity and competence of oocytes, have shown not alteration in the number of mature oocytes retrieved and fertilization rates. The short-term follow-up of patients with breast cancer who undergo ovarian stimulation with letrozole plus gonadotropins for fertility preservation, do not show an increased risk of recurrence of breast cancer (65).
4.3 MEDICAL CONSIDERATIONS IN CANCER PATIENTS UNDERGOING CONTROLLED OVARIAN STIMULATION.
Cancer itself can be responsible for a variety of consequences occurring during ovarian stimulation. It’s necessary to try to prevent any life-threatening complications, recognize them, and manage them.
Oncological patients undergoing ovarian stimulation are at an increased risk of thromboembolic events, due to a hypercoagulable state induced by their malignancy and estradiol serum levels (66). These patients may require anticoagulation during time of COS. Currently, there are no guidelines for anticoagulation during COS. In clinical practice, prophylactic low-molecular-weight heparin should be started with ovarian stimulation in high-risk patient and the last dose of medication should be administered to patients 24 hours before the oocyte retrieval and restarted 12 hours after the retrieval and can be continued until E2 returns to its baseline level (67). The other strategy of preventing thromboembolic events is to use letrozole during COS.
Malignancies with bone marrow or liver involvement may create bleeding during oocyte retrieval due to thrombocytopenia, platelet dysfunction, or defective coagulation
factor synthesis. Platelet count and coagulation panel should be tested before COS in patients with hematologic malignancies or with malignancies involving the liver. Platelet or fresh frozen plasma transfusion should be performed before oocyte retrieval to prevent excessive bleeding in these patients as needed (67).
Higher risk of pelvic infection after oocyte retrieval can be a problem especially in cancer patients with neutropenia. In this case, consultation for granulocyte colony stimulating factor use should be obtained, and prophylactic antibiotics should be given before oocyte retrieval (67).
