Ovarian stimulation in cancer patients

Hakan Cakmak, M.D. and Mitchell P. Rosen, M.D.

Department of Obstetrics, Gynecology, and Reproductive Sciences, Division of Reproductive Endocrinology and Infertility,University of California, San Francisco, California

The patients referred for fertility preservation owing to a malignant disease do not represent the typical population of subfertile patientstreated in IVF units. Cancer may affect multiple tissues throughout the body and can result in a variety of complications during con-trolled ovarian stimulation. Determination of the controlled ovarian stimulation protocol and gonadotropin dose for oocyte/embryo

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cryopreservation requires an individualized assessment. This review highlights the newprotocols that are emerging to reduce time constraints and emphasizes managementconsiderations to decrease complications. (Fertil Steril� 2013;99:1476–84.�2013 by AmericanSociety for Reproductive Medicine.)Key Words: Cancer, fertility preservation, ovarian stimulation, random start

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C ancer is not uncommon andno longer considered to be anincurable disease among

reproductive-age women. More than790,000 new female cancer cases wereestimated to be diagnosed in 2012 inthe United States (1). Approximately10% of female cancer cases occur underthe age of 45 years (2). Over thepast three decades, there has beena remarkable improvement in thesurvival rates owing to progress indiagnosing certain cancers at an earlierstage and improvements in treatment(2). From 2002 to 2012, 83% of womenyounger than 45 years diagnosed withcancer survived (2). As a consequenceof the increase in the number ofpatients surviving cancer, greaterattention has been focused on thedelayed effects of cancer treatmentson the quality of future life of thesurvivor (3, 4).

The treatment for most of thecancer types in reproductive-agewomen involves either removal of thereproductive organs or cytotoxic

Received January 29, 2013; revised March 16, 2013; aH.C. has nothing to disclose. M.P.R. has nothing to dReprint requests: Mitchell P. Rosen, M.D., Departme

Sciences, 2356 Sutter St., 7th Floor, San Francucsf.edu).

Fertility and Sterility® Vol. 99, No. 6, May 2013 0015Copyright ©2013 American Society for Reproductivehttp://dx.doi.org/10.1016/j.fertnstert.2013.03.029

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treatment (chemotherapy and/or radio-therapy) that may partially or defini-tively affect reproductive function (5).The ovary is particularly sensitive tothe adverse effects of cancer treatmentsbecause of the set number of folliclespresent in the postnatal ovary (5).Reproductive lifespan is determined bythe follicle pool, and therefore, cancertreatments that cause folliculardepletion accelerate the onset ofmenopause (6). The irreversible gona-dotoxic effects of some of thechemotherapeutic agents arewell docu-mented, particularly for alkylatingagents (e.g., cyclophosphamide, busul-fan, and ifosfamide), which are com-mon components of chemotherapy forbreast cancer, lymphomas, leukemia,and sarcomas (7, 8). Pelvic radiationtherapy is also known to causefollicular destruction, and exposure to5–10 Gy pelvic radiation appears to betoxic to oocytes, resulting inpremature ovarian insufficiency inmany women (5). The risk of ovarianfailure following cancer therapy

ccepted March 18, 2013.isclose.nt of Obstetrics, Gynecology, and Reproductiveisco, California 94115 (E-mail: rosenm@obgyn.

-0282/$36.00Medicine, Published by Elsevier Inc.

appears to be dose related, and theeffect depends on age and ovarianreserve at the time of treatment (9).

Early loss of ovarian function notonly puts the patients at risk formenopause-related complications ata very young age, but is also associatedwith loss of fertility (8). In addition,women in the United States have beendelaying initiation of childbearing tolater in life for social and financialreasons. The birth rate for womenaged 30–34 years increased from80.8 births per 1,000 women in 1990to 96.5 births per 1,000 women in2011 (10). Similarly, the rate for womenaged 35–44 years rose 54% from 1990to 2011, increasing from 37.2 to57.5 births per 1,000 women (10). Inother words, more women in their30s to early 40s are attempting to getpregnant for the first time than everbefore. Because the incidence of mostcancers increases with age and manywomen wish to conceive using theirown oocytes, delayed childbearingresults in more female cancer survivorsinterested in fertility preservation.

Multiple strategies have emergedaiming to preserve fertility in womenwith different types of malignancies.These include embryo and oocyte cryo-preservation, cortical and whole ovarycryopreservation, ovarian transplanta-tion, ovarian transposition, and GnRH

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agonist protection (11). Currently, embryo and mature oocytecryopreservation following in vitro fertilization (IVF) are theonly techniques endorsed by the American Society of Repro-ductive Medicine, and the other methods are still consideredto be investigational (12, 13).

Controlled ovarian stimulation (COS) for embryo or matureoocyte cryopreservation is themost preferredmethod for fertilitypreservation in cancer patients, owing to its higher success ratescompared with other, more experimental, technologies (12, 13).Therefore, it should be recommended as long as the patient'smedical condition does not preclude safely performing COS oroocyte retrieval and the patient has adequate time to undergoCOS and oocyte retrieval (12, 13). To facilitate initiation ofovarian stimulation and avoid unnecessary delay, promptconsultation with a reproductive endocrinologist andcoordinationof care arenecessaryafter the cancer diagnosis (14).

The number of oocytes retrieved and their quality areimperative factors predicting the potential efficacy of thefertility preservation procedure. Consequently, informationregarding the expected ovarian performance after COS iscrucial when consulting with the patient. Therefore, theassessment of ovarian reserve with the use of antral folliclecount (AFC) and/or antim€ullerian hormone (AMH) beforeovarian stimulation is necessary to provide more accurateprediction of ovarian response to COS and to determine theCOS protocol and starting gonadotropin dose (15).

TABLE 1

Comparison of antral follicle count (AFC) between cancer patientsand healthy women in different age groups (26).

Age (y)

Cancer patients Healthy women

P valuen Median Range n Median Range

25–30 33 14 1–58 205 20 4–58 < .00131–35 47 11 0–54 216 15 5–48 .00436–40 49 7 0–40 227 12 0–52 < .00141–45 20 7 1–20 161 6 1–22 .789Cakmak. Ovarian stimulation in cancer patients. Fertil Steril 2013.

RESPONSE TO OVARIAN STIMULATION INCANCER PATIENTSIn cancer patients, both the specific malignancy and thepatient's multisystemic condition may have an impact onthe response to ovarian stimulation (16). The increasedcatabolic state, malnutrition, and increased stress hormonelevels associated with the malignancy may affect thehypothalamic-gonadal axis and decrease fertility (17).Possible adverse association between the presence ofa neoplastic process and ovarian reserve or oocyte quality isalso suggested (17–19). There are mixed reports about howcancer patients respond to the IVF stimulation protocols:some reporting no significant change (20–22) and othersdemonstrating worse ovarian response in cancer patientscompared with age-matched healthy women (19, 23). Ina recent meta-analysis conducted on seven retrospectivestudies, women with malignancies had lower numbers of totaloocytes (11.7 � 7.5 vs. 13.5 � 8.4) and mature oocytesretrieved (9.0� 6.5 vs. 10.8� 6.8) after COS for fertility pres-ervation compared with healthy age-matched patients (16).Moreover, the relative risk of poor response leading to cyclecancellation was higher in cancer patients than in the controlgroup (risk ratio 1.32, 95% confidence interval 0.78–2.17)although the observed difference did not reach statisticalsignificance, possibly due to the small size of the groups (16).

BRCA genes play an essential role in double-strand DNAbreak repair, and their mutations are associated with anincreased risk of breast and ovarian cancers (24). In patientswith BRCA mutations, oocytes may be more prone to DNAdamage, clinically manifesting as diminished ovarian reserveor earlier menopause (25). In BRCA mutation–positive breast

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cancer patients, a low response to ovarian stimulationoccurred more frequently than in patients without BRCAmutations (33.3% vs. 3.3%) or in breast cancer patients nottested for their BRCA status (2.9%) (18). Interestingly, allBRCA mutation–positive patients with a low response toovarian stimulation and requiring higher doses of gonadotro-pins for their stimulation had BRCA-1 mutations, and a lowresponse was not encountered in women who were positivefor only a BRCA-2 mutation (18).

None of the studies mentioned above compared the ovar-ian reserve of cancer patients with healthy age-matchedwomen. In a recent study, ovarian reserve assessed withAMH was found to be significantly lower in patients withlymphoma before chemotherapy compared with healthycontrol subjects (26). Moreover, we previously demonstratedthat women with cancer before gonadotoxic therapy mayhave significantly lower AFC compared with healthy womenaged 25–40 years (Table 1) (27). This lower AFC in cancerpatients may be explained by either accelerated follicle lossor a defect in recruitment of antral follicles owing to diseasestate. It is well established that AFC correlates directly withnumber of follicles, number of mature oocytes retrieved,and number of embryos obtained during an IVF cycle (28).In our clinical experience, although the number of matureoocytes retrieved and embryos obtained may be lower incancer patients compared with healthy individuals, they areappropriate for their given AFC. Moreover, their response tothe gonadotropins and mature oocyte yield (i.e., number ofmetaphase II [MII] oocytes/AFC) are similar to those of thehealthy women. Therefore, if lower oocyte and embryonumbers in patients with malignancy during an IVF cycleare true, this is not due to poor response to ovarian stimula-tion, but likely the result of decreased number of availableantral follicles to be stimulated.

In conclusion, candidates for fertility preservationbecause of malignancy, especially BRCA-1 mutation carriers,should be informed that the expected number of oocytesretrieved after COS may be lower compared with healthypatients of similar age. However, more studies are needed toconfirm these findings.

GONADOTROPIN DOSE DURING OVARIANSTIMULATIONMaximizing the number of embryos and oocytes cryopre-served during a fertility preservation cycle is extremelyimportant, not only because the patient usually has a single

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cycle opportunity owing to time constraints, but also toincrease the chance of future pregnancies. Using higher dosesof gonadotropins can be one of the strategies to increase theembryo and oocyte yield per cycle. In a study comparinga low-dose antagonist IVF protocol (150 IU FSH) anda higher-dose antagonist IVF protocol (>150 UI) in cancerpatients, although the number of follicles>17mmwas greaterin the higher-dose group, there was no difference in numbersof oocytes (13.3� 8.7 vs. 12.3� 8.0) or embryos (6.3� 4.7 vs.5.4 � 3.8) generated between the two groups (29). That studysuggests that the use of higher doses of gonadotropins maynot necessarily result in higher oocyte/embryo yield consis-tent with the theory that higher doses of gonadotropins maystimulate the recruitment of chromosomally abnormal or in-competent oocytes (30). However, in patients with decreasedovarian reserve as assessed with the use of AFC and/orAMH, higher doses of gonadotropins may be required.

Conventional and random-start antagonist IVF protocols for cancerpatients undergoing fertility preservation. COS can be started withspontaneous menses (A) or with menses following luteolysisinduced by GnRH antagonist (B). COS can also be initiated in thelate follicular (C) or luteal phase following spontaneous LH surge(D) or after ovulation induction with hCG or GnRH agonist (E).Cakmak. Ovarian stimulation in cancer patients. Fertil Steril 2013.

OVARIAN STIMULATION PROTOCOLSConventional Controlled Ovarian Stimulation

The choice of the specific COS protocol is generallydetermined based on the policy of preferences in each IVFcenter and influenced by the time available until the initiationof radio/chemotherapy. Although multiple different COSprotocols are used, the majority of patients are treated witha GnRH antagonist–based protocol, which likely allows theshortest deferral of the initiation of radio/chemotherapy. Todate, there are no studies comparing agonist and antagonistprotocols in women with cancer.

Traditional ovarian preparation for IVF requires 9–14days of ovarian stimulation with exogenous gonadotropins,preceded by ovarian suppression with GnRH agonists for�2 weeks to prevent premature ovulation. Because GnRHagonist is initiated in the luteal phase of the cycle, this mayadd up to 3 additional weeks to the process, depending onwhen the patient presents for treatment.

The development of GnRH antagonists has significantlydecreased the interval from patient presentation toembryo/oocyte cryopreservation (31). In contrast to GnRHagonists, GnRH antagonists immediately suppress pituitaryrelease of FSH and LH and do not require the 10–14 daysof administration before gonadotropin initiation. GnRHantagonists are initiated to prevent premature LH surgewhen the size of the lead follicle reaches 12–14 mm atapproximately day 6 of gonadotropin stimulation whichbegins on day 2–3 of a menstrual cycle (Fig. 1A). Thisapproach still requires awaiting menses before initiatinggonadotropins, but it decreases the interval to oocyte retrievalcompared to traditional IVF stimulation protocols.

The use of GnRH antagonists during the preceding lutealphase was explored originally for cancer patients and then forpoor IVF responders as a method to improve ovarianstimulation by inducing corpus luteum breakdown andsynchronizing the development of the next wave of follicles(32, 33). For cancer patients, the idea of administering GnRHantagonists in the luteal phase was driven more by minimizingpotential delays for cancer treatment (32). If a GnRH

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antagonist (e.g., single dose of 3mg cetrorelix subcutaneously) isgiven during themidluteal phase,menses ensues a few days later(32, 33) (Fig. 1B). As a result, ovarian stimulation would beinitiated more quickly and a GnRH antagonist would berestarted in a standard fashion, when the lead follicle is at 12–14 mm to prevent premature LH surge (33).

Random-Start Controlled OvarianHyperstimulation

Conventionally, ovarian stimulation for oocyte/embryocryopreservation is initiated at the beginning of the follicularphase with the idea that this optimizes clinical outcomes; itmay require 2–6 weeks depending on the woman's menstrualcycle phase at the time of planning the treatment. Adhering tothis convention may result in either significant delay ofcancer treatments or forgoing of fertility preservation owingto time constraints. For cases not desirable to wait for the nextmenstrual period to start a stimulation protocol owing to theurgency of the cancer treatment, random-start stimulationprotocols have been proposed (34–36).

In a small prospective multicenter study (n ¼ 40), a novelprotocol for cancer patients that initiated ovarian stimulationduring the luteal phase of the menstrual cycle was described(36). Cancer patients in the luteal phase were started on GnRHantagonists todown-regulateLHand initiate luteolysis. Simulta-neously, follicular stimulation was initiated with recombinantFSHonly, thus avoidingexogenousLHactivitywhichmight pre-vent luteolysis. Comparedwith cancer patients stimulatedduringthe follicular phase (n¼ 28) with either a short ‘‘flare-up’’ proto-coloranantagonist protocol, the luteal-phasegroup (n¼12)hadsimilar number of aspirated oocytes, number ofMII oocytes, andfertilization rate (36).

A report of three breast cancer patients evaluated theeffectiveness of initiating ovarian stimulation at the time ofpatient presentation (menstrual cycle days 11, 14, and 17)rather than waiting for spontaneous menses (35). GnRHantagonist was started to prevent premature LH surge whenthe lead follicle measured>13 mm. The random-start ovarianstimulation resulted in a reasonable ovarian response, with7–10 embryos cryopreserved per patient (35).

TABLE 2

Comparison of characteristics and outcomes of conventional and random

Conventional star(n [ 87; 101 cycl

Age (y) 33.9 � 5.2AFC 13 (9–19)Days of ovarian stimulation 9 (8–10)Total dose of gonadotropins (IU) 3,386 � 1,085Follicles R13 mm 12 (6–17)Oocytes retrieved 15 (9–23)Mature oocytes (MII) retrieved 11 (6–16)Oocyte/AFC ratio 1.1 (0.8–1.7)Mature oocyte/AFC ratio 0.8 (0.5–1.1)Fertilization rate after ICSI (2PN/MII) 0.77 � 0.22Note: Data are presented as mean� SD or median (interquartile range) (32). 2PN¼ two pronuclei; Asignificant.

Cakmak. Ovarian stimulation in cancer patients. Fertil Steril 2013.

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The recent report presenting our clinical experience withrandom-start ovarian stimulation demonstrated that latefollicular or luteal phase–start antagonist IVF cycles wereas effective as conventional (i.e., early follicular)–startantagonist IVF cycles in cancer patients (34). The latefollicular phase was defined as after menstrual cycle day 7with emergence of a dominant follicle (>13 mm) and/orprogesterone level <2 ng/mL. If the cancer patient presentedin the late follicular phase, we proceeded with one of thefollowing treatment plans. 1) Ovarian stimulation was startedwithout GnRH antagonist if the follicle cohort following thelead follicle was<12 mm and continued to be<12 mm beforespontaneous LH surge (Fig. 1C). After the LH surge, GnRHantagonist was started later in the cycle when the secondaryfollicle cohort reached 12 mm to prevent premature secondaryLH surge. Or 2) ovulation was induced with hCG or GnRHagonist and ovarian stimulation was started in 2–3 days inthe luteal phase (Fig. 1E) (34). If the cancer patient presentedin the luteal phase or the ovulation was induced, GnRHantagonist administration was initiated similarly toconventional ovarian stimulation later in the cycle when thesecondary follicle cohort reached 12 mm to preventpremature secondary LH surge (Fig. 1D and E) (34). Thenumbers of total and mature oocytes retrieved, oocyte yield(i.e., number of MII oocytes/AFC), and fertilization rates weresimilar between groups (34) (Table 2). However, the length ofovarian stimulation was �2 days longer, and therefore, thetotal dose of gonadotropin used was significantly higher inlate follicular and luteal phase–start groups compared withthe conventional-start group (34) (Table 2). In contrast to ear-lier belief, the presence of corpus luteum or luteal-phase pro-gesterone levels did not adversely affect the folliculardevelopment, oocyte yield, or possibility of having secondaryspontaneous LH surge in random-start patients (34).

Overall, this approach provides a significant advantageby decreasing total time for the IVF cycle, and in urgent set-tings, ovarian stimulation can be started at a random cycledate for the purpose of fertility preservation withoutcompromising oocyte yield and maturity. This is consistentwith a newer concept of ovarian physiology, which indicatesthat there are multiple waves of follicle recruitment during

start antagonist IVF cycles in cancer patients.

tes)

Random start(n [ 24; 24 cycles) P value

34.6 � 5.0 NS11.5 (6–16) NS11 (10–12) < .001

4,201 � 1,147 .00110 (8–15.5) NS

12.5 (9–20.5) NS9 (5–14.5) NS

1.2 (0.9–1.7) NS0.8 (0.6–1.2) NS0.87 � 0.15 NS

FC¼ antral follicle count; ICSI¼ intracytoplasmic sperm injection; MII¼metaphase II; NS¼ not

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each menstrual cycle (37). Additional clinical studies areneeded to assess the efficacy of this strategy, especiallyregarding the rates of clinical pregnancy and of live-borninfants originating from the use of cryopreserved embryosand of oocytes obtained by random start ovarian stimulation.

Controlled Ovarian Stimulation in Patients withEstrogen-Sensitive Cancers

During COS, there is a potential risk that the supraphysiologicE2 levels resulting from ovarian stimulation with gonadotro-pins may promote the growth of estrogen-sensitive tumors,such as endometrial and estrogen receptor–positive breastcancers (15). The rise in E2 is directly proportional to thenumber of follicles recruited to grow; therefore, alternativeand potentially safer protocols have been introduced forfertility preservation for estrogen-sensitive cancer patients,including natural-cycle IVF (without ovarian stimulation),stimulation protocols with tamoxifen alone or combinedwith gonadotropins, and stimulation protocols witharomatase inhibitors to reduce the estrogen production (38).

Natural-cycle IVF gives only one or two oocytes orembryos per cycle and has a high rate of cycle cancellation.Therefore, this technique would likely be ineffective andis not recommended, especially when a chemotherapytreatment is imminent and the patient does not have a chancefor a second cycle of IVF treatment.

Tamoxifen, a nonsteroidal triphenylethylene compoundrelated to clomiphene, has a well known antiestrogenic actionon breast tissue with the inhibition of growth of breast tumorsby competitive antagonismof estrogenat its receptor site, and itis accepted as the first-line drug in hormonal prevention andtreatment of estrogen receptor–positive breast cancer (39). Ta-moxifen, besides its effect in the breast, also has an antagonistaction in the estrogen receptors in the central nervous systemsimilar to that of clomiphene. The selective antagonist actionof tamoxifen interferes with the negative feedback of the estro-gen on the hypothalamic-pituitary axis, leading to an increaseinGnRHsecretion from the hypothalamus and a subsequent re-lease of FSH from the pituitary-stimulating follicular develop-ment. Tamoxifen can be used for COS alone starting onday 2–5of the menstrual cycle in doses of 20–60 mg/d, or in combina-tion with gonadotropins, similarly to the use of clomiphene(38). Even though peak E2 levels in ovarian stimulation withtamoxifen are not altered, owing to its antiestrogenic effecton breast tissue, it is desirable to be used in estrogen recep-tor–positive breast cancer patients. Ovarian stimulation withthe use of tamoxifen for fertility preservation in cancer patientswas shown to increase the mature oocyte and embryo yieldcompared with natural-cycle IVF (1.6 vs. 0.7 and 1.6 vs. 0.6,respectively) and reduce cycle cancellations (40). As expected,combined protocol with tamoxifen and gonadotropins furtherincreased the number of cryopreserved oocytes and embryos(5.1 vs. 1.5 and 3.8 vs. 1.3, respectively) (41).

Aromatase is a cytochrome P450 enzyme complex thatcatalyzes the conversion of androstenedione and testosteroneto their respective estrogenic products estrone and E2 (42).Aromatase inhibitors, such as letrozole, markedly suppressplasma estrogen levels by competitively inhibiting the

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activity of the aromatase enzyme (43). Aromatase inhibitorssignificantly reduce the risk of recurrence in postmenopausalwomen with hormone receptor–positive breast cancer owingto profound estrogen deprivation, especially with third-generation inhibitors (i.e., anastrozole and letrozole) (44).Centrally, aromatase inhibitors release the hypothalamic-pituitary axis from estrogenic negative feedback, increasethe secretion of FSH by the pituitary gland, stimulate folliclegrowth, and, thereby, can be used for ovulation induction(45). In patients with estrogen-sensitive cancers, the mainadvantage of adding daily letrozole to gonadotropins in ovar-ian stimulation protocols is to decrease serum E2 levels to becloser to that observed in natural cycles (i.e., E2 <500 pg/mL)without affecting oocyte or embryo yield (46, 47). Stimulationprotocols using letrozole alongside with gonadotropins arecurrently preferred over tamoxifen protocols as treatmentwith letrozole results in a higher number of oocytesobtained and fertilized when compared to tamoxifenprotocols (41). In a study comparing the efficacy of theletrozole plus gonadotropin protocol in breast cancerpatients and the standard IVF protocol in age-matchednoncancer patients with tubal-factor infertility, the breastcancer patients started to receive letrozole (5 mg/d) onmenstrual cycle day 2 or 3, FSH (150–300 IU/d) was added2 days later, all medications were discontinued on the dayof hCG trigger, and letrozole was reinitiated after oocyteretrieval and continued until E2 levels fell to <50 pg/mL(47). This letrozole plus gonadotropin protocol resulted insimilar number of total oocytes retrieved and length ofovarian stimulation compared with standard IVF protocol(47). As expected, peak E2 levels were significantly lowerin the breast cancer patients receiving letrozole plusgonadotropin compared with the standard IVF group(483 � 278.9 pg/mL vs. 1,464.6 � 644.9 pg/mL) (47). Thestudies assessing the effect of letrozole on oocyte maturityand competence demonstrated that the addition of letrozoledid not change numbers of mature oocytes retrieved andfertilization rates (47, 48). Similarly, in our practice weobserved similar oocyte maturity (MII oocytes/total oocytesretrieved; 0.68 � 0.19 vs. 0.71 � 0.23) and fertilization rate(0.77 � 0.22 vs. 0.78 � 0.24) in intracytoplasmic sperminjection cycles with and without letrozole (unpublisheddata). The short-term follow-up of breast cancer patients,who had undergone ovarian stimulation with letrozole plusgonadotropins for fertility preservation has not been shownto raise the risk of breast cancer recurrence (49). In addition,COS with aromatase inhibitors in combination with gonado-tropins has been safely used for embryo cryopreservation inendometrial cancer patients (50).

Letrozole suppresses plasma E2 levels significantly atdoses of 0.1–10 mg/d (51). In our clinic, we start letrozole at2.5–5 mg/d, depending on the ovarian reserve of the patient,with the ovarian stimulation (Fig. 1). Given the importance ofkeeping E2 levels close to that observed in natural cycles inpatients with estrogen-sensitive cancers, we check E2 levelsin every clinic visit and titrate letrozole dose up to 10 mg/dto keep E2 levels <500 pg/mL (46). These letrozole dosesare well tolerated by the patients during ovarianstimulation without any side effects. In addition, the mature

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oocyte/embryo yield after COS is not affected by letrozole atany dose used in our clinical practice. We also consider con-tinuing letrozole after the oocyte retrieval if serum E2 levelsare still elevated (i.e., E2 >500 pg/mL). In our experience,even if E2 levels are >500 pg/mL before retrieval, only a mi-nority of patients requires letrazole after retrieval. Discontin-uation of letrazole can either be at menses or with initiation ofchemotherapy. In contrast, anastrozole—another third-generation aromatase inhibitor—failed to adequately suppressE2 levels during COS, despite gradually increasing the dose ofanastrozole to a maximum of 10 mg/d, and therefore we donot recommend its use in fertility preservation cycles (52).

In summary, COS with letrozole plus gonadotropins inpatients with estrogen-sensitive cancers undergoing fertilitypreservation is safe, well-tolerated, and yields similarnumber of oocytes and embryos compared with standardprotocols while minimizing the risk of high estrogen exposureand not increasing the recurrence of cancer in the short term.Therefore, we highly recommend the routine use of letrozoleduring COS for fertility preservation in patients withestrogen-sensitive cancers.

Prevention of Ovarian HyperstimulationSyndrome in Cancer Patients

Ovarian hyperstimulation syndrome (OHSS) is the mostserious complication of ovarian stimulation and can beassociated with intravascular depletion, ascites, liverdysfunction, pulmonary edema, electrolyte imbalance, andthromboembolic events. Although OHSS is often self-limited with spontaneous resolution within a few days, severedisease may require hospitalization and intensive care.Selecting the appropriate ovarian stimulation regimen canbe challenging in embryo/oocyte cryopreservation becauseit is important to balance the risk of OHSS and obtainingsufficient number of oocytes or embryos to maximize thechance of a successful pregnancy in the future. The impactof OHSS can be profound in cancer patients because it mayresult in delaying or complicating planned life-saving cancertherapy (53).

Triggering the final oocyte maturation with hCG carriesthe well known risk of inducing OHSS (54). GnRH agonistalso induces this final oocyte maturation by promoting therelease of endogenous gonadotropin stores from the hypoph-ysis as long as the pituitary gonadotropin receptors are notdown-regulated and can be used as an alternative to hCG(54). GnRH agonist trigger in GnRH antagonist–basedprotocols dramatically reduces the risk of OHSS, owing tothe short half-life of GnRH agonist–induced endogenousLH surge (55). Moreover, there was a significantly lowerrate of moderate/severe OHSS in the GnRH agonistgroup compared with the patients receiving hCG trigger(3.7% vs. 21.3%) (56). GnRH agonist trigger is particularlyconvenient in cancer patients pursuing oocyte or embryobanking, because luteal support is not needed to sustaina pregnancy. In a study comparing GnRH agonist and hCGas the trigger for oocyte maturation in fertility preservationcycles, GnRH agonist trigger resulted in at least similarnumbers of mature oocytes and cryopreserved embryos

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compared with hCG (56). In addition, although hCG potenti-ates the endogenous production of estrogen during the lutealphase owing to its longer half-life, GnRH agonist–inducedendogenous LH may result in lower estrogen production,which may be an advantage for patients with estrogen-sensitive cancers (54).

However, in our experience we have observed triggerfailures with GnRH agonist trigger at both 1 mg and 4 mgdosing. The likely reason is that GnRH agonist is able tobind to only a portion of the receptors owing to competitionwith GnRH antagonist, yielding a limited LH surge (57). It ispossible that with the increase in dose of GnRH agonist orwith hCG supplementation (%1,500 IU) at the time of trigger,there will be fewer failures. Because of the possibility offailure, we do not routinely recommend GnRH agonist triggerfor all patients. In our current practice, 4 mg leuprolideacetate is being used only in patients with high risk of OHSS.

The number of follicles, more specifically the follicularpattern, in combination with serum E2 levels predicts OHSSwith high sensitivity and specificity (58, 59). However, onecaveat is that cotreatment with aromatase inhibitors limitsthe use of E2 level to help predict OHSS. In this scenario, itis important to rely on the follicular pattern and the rate ofE2 rise rather than the absolute of serum E2 levels. If theE2 levels are rising rapidly while administering letrozole,especially in the presence of a high number of smallfollicles, the patient should be considered to be be at risk forOHSS and GnRH agonist trigger should be used to lowerthat risk.

In conclusion, we recommend GnRH agonist trigger inGnRH antagonist–based fertility preservation cycles onlyfor women who are at risk for OHSS. The trigger must beconfirmed the next morning by measuring serum LH level.In the case of a GnRH agonist trigger failure determined bylow post-trigger LH (in our clinic, we use a cutoff LH levelof <12 mIU/mL), hCG (2,500–5,000 IU) trigger can be givenon the same day (60). If the patient has relatively lowpost-trigger LH level, but >12 mIU/mL, closer attentionshould be given to the oocyte yield during oocyte retrieval.If no or an inappropriately low number of oocytes are re-trieved after aspirating a couple of mature-size follicles, theoocyte retrieval should be stopped, oocyte maturation shouldbe triggered again by administering hCG (2,500–5,000 IU)owing to the possibility of failing to trigger oocyte maturationwith GnRH agonist, and then oocyte retrieval should beattempted again after 34–36 hours (60).

Medical Considerations in Cancer PatientsUndergoing COS

The patients referred for fertility preservation owing toa malignant disease do not represent the typical populationof subfertile patients treated in IVF units. Cancer may affectmultiple tissues throughout the body and can result in varietyof complications during COS. Therefore, the goals during COSin cancer patients are to prevent these serious life-threateningcomplications with prophylaxis, and to recognize andmanage them effectively when they occur.

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Cancer patients undergoing COS are at increased risk ofthromboembolic events because of a hypercoagulable stateinduced by their malignancy and supraphysiologic serumE2 levels (61). Therefore, these patients may require anticoa-gulation around the time of COS. Currently, there are noguidelines for anticoagulation during COS. However, thesafety and efficacy of anticoagulation during COS and afteroocyte retrieval have been reported (62). In our practice, westart prophylactic low-molecular-weight heparin withovarian stimulation in high-risk patients and instruct thepatient to take their last dose of medication 24 hours beforethe oocyte retrieval. Low-molecular-weight heparin isreinitiated 12 hours after the retrieval and can be continueduntil E2 returns to its baseline level. The other strategy ofpreventing thromboembolic events is to use letrozole duringCOS to keep E2 levels close to those observed in natural cycles.Letrozole at 2.5 or 5 mg/d can be started with ovarianstimulation, as in patients with estrogen-sensitive malignan-cies, and can be titrated up to 10 mg/d to keep E2 levels<500 pg/mL. Letrozole can also be continued after oocyteretrieval for up to a week depending on the E2 level at thetime of ovulation induction.

Malignancies with bone marrow infiltration or liverinvolvement may create a tendency toward bleeding duringoocyte retrieval owing to thrombocytopenia, plateletdysfunction, or defective coagulation factor synthesis.Therefore, platelet count and coagulation panel should betested before COS in patients with hematologic malignanciesor with malignancies involving the liver. Platelet or freshfrozen plasma transfusion should be performed before oocyteretrieval to prevent excessive bleeding in these patients asneeded.

Higher risk of pelvic infection after oocyte retrieval canbe a problem especially in cancer patients with neutropenia.Therefore, absolute neutrophil count should be evaluatedbefore COS in cancer patients with possible bone marrowinfiltration. In the case of neutropenia, consultation fromthe patient's oncologist for the use of granulocyte colony-stimulating factor to increase the neutrophil count shouldbe obtained, and prophylactic antibiotics should be givenbefore oocyte retrieval to decrease the risk of infection.

Some of the cancer-related medical conditions, includingrespiratory dysfunctions due to tracheal compression,mediastinal mass, or large pleural effusion, and vasculardisturbances, as in superior vena cava syndrome, maypreclude safe administration of conscious sedation duringoocyte retrieval. Anesthesia consultation should be obtainedin advance for the patients with these conditions. If safetyand difficult intubation in an emergency situation areconcerns, the oocyte retrieval should be performed eitherunder general anesthesia with endotracheal intubation oronly with local anesthesia.

The patients with recent mastectomies for breast cancermay have special needs during COS. Owing to decreasedmobility, they may need more assistance during office visits.Intravenous line placements to the upper extremity on thesame side of the axillary node dissection should be avoided,owing to concerns of lymphatic system damage andinadequate lymphatic flow. In patients who have had

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transverse rectus abdominis myocutaneous flap for breastreconstruction after mastectomy, abdominal distention, andtherefore OHSS, should be avoided to prevent wounddehiscence.

The medication list for all cancer patients should bereviewed before COS. Antiepileptic medications shoulddefinitely be continued during COS in patients with braintumor owing to increased risk of seizures. The use of Imatinib(Gleevec), a specific inhibitor of constitutively activatedBcr-Abl tyrosine kinase used in chronic myelogenousleukemia, should be temporarily stopped during COS owingto its adverse effect on ovarian hormone production andoocyte recovery (63).

CONCLUSIONSGiven the importance of reproduction for many youngpatients faced with cancer, counseling regarding fertilitypreservation is an essential part of comprehensive cancercare. Embryo cryopreservation is the most established methodfor fertility preservation, and oocyte cryopreservation hasgained efficacy and is now offered at many centers.Determination of the COS protocol and gonadotropin dosefor oocyte/embryo cryopreservation requires an individual-ized assessment. Maximizing the number of embryos andoocytes cryopreserved during a fertility preservation cyclewithout causing OHSS is extremely important, becausemost patients have only a single cycle opportunity owing totime constraints before starting their oncologic treatment.In urgent settings, random-start ovarian stimulation isemerging as a new technique for the purpose of fertilitypreservation without compromising oocyte yield andmaturity. Letrozole plus gonadotropin protocol is an effectivemethod for safely inducing COS in patients with estrogen-sensitive cancers undergoing fertility preservation. Althoughnewly developed protocols are efficient in inducing COS andobtaining appropriate number of oocytes/embryos, onlya minority of the patients have undergone thawing andembryo transfer, so there are not enough consistent datareported to evaluate the implantation and pregnancy ratesof these new protocols. This issue should be appropriatelyaddressed in the future to enable prediction of the numberof oocytes/embryos needed to be preserved to offer a realisticchance for later reproduction in these patients.

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