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Use of an aromatase inhibitor in patients with polycystic ovary syndrome: a prospective randomized trial
Use of an aromatase inhibitor in patients with polycystic ovary syndrome: a prospective randomized trial Ülkü Bayar, M.D.,a Mustafa Basaran, M.D.,a Sibel Kiran, M.D.,b Ayhan Coskun, M.D.,c and Sener Gezer, M.D.a Zonguldak Karaelmas University Faculty of Medicine, a Department of Obstetrics and Gynecology and b Department of Public Health, Zonguldak; and c SB Ataturk Hospital, Adana, Turkey
Objective: To compare the use of an aromatase inhibitor (letrozole) with the use of clomiphene citrate (CC). Design: Prospective randomized study. Setting: An infertility clinic in a university hospital. Patient(s): Seventy-four consecutive infertile patients with polycystic ovary syndrome were recruited. Thirtyeight patients were randomized to the letrozole group (99 cycles), and the remaining patients were recruited to the CC group (95 cycles). Intervention(s): The aromatase inhibitor letrozole (2.5 mg/d) and CC (100 mg/d) were administered orally on days 3–7 of menses. Main Outcome Measure(s): Number of follicles, endometrial thickness, E2 levels on hCG day, and pregnancy rates among both groups. Result(s): Ovulation occurred in 65.7% (65/99) of letrozole cycles and in 74.7% (71/95) of CC cycles. The median (minimum–maximum) number of follicles sized ⬎15 mm in diameter on the day of hCG administration were 1 (0 – 4) and 1 (0 –5) in the letrozole and CC groups, respectively. On the day of hCG administration, median serum E2 concentrations in the letrozole and CC groups were statistically significantly different: 189 pg/mL (18 –1,581 pg/mL) and 386 pg/mL (27– 6,190 pg/mL), respectively. The median serum E2 concentrations per follicle sized ⬎15 mm in diameter on the day of hCG also statistically significantly differed between the letrozole and CC groups: 160 pg/mL (18 – 808 pg/mL) and 281 pg/mL (27–2,615 pg/mL), respectively. The median endometrial thickness on the day of hCG did not significantly differ between the CC and letrozole groups; it was 8 mm. Pregnancy was achieved in nine cycles (9.1%) of the letrozole group and in seven cycles (7.4%) of the CC group, which also was not a statistically significant difference. Conclusion(s): The aromatase inhibitor letrozole may be an acceptable alternative to CC as an ovulation-induction drug in patients with PCOS. (Fertil Steril威 2006;86:1447–51. ©2006 by American Society for Reproductive Medicine.) Key Words: Letrozole, clomiphene citrate, PCOS, ovulation induction
Polycystic ovarian syndrome (PCOS) is characterized by chronic anovulation, hyperandrogenism, and polycystic ovaries. Although considerable progress has been made toward a better understanding of pathogenesis, the exact cause (or causes) still is unknown (1). Clomiphene citrate (CC) frequently is used for ovulation induction and is highly effective in initiating ovulation in patients with PCOS (2). However, despite a 75%– 80% ovulation rate with CC use, the cumulative pregnancy rate after 6 months of treatment is only 40%– 45% (3). In patients who do not respond to treatment after four to six cycles of CC, gonadotropins usually are administered for an additional six cycles (4, 5). In PCOS patients, as a result of the increased sensitivity of ovaries to gonadotropin stimulation, the risks of ovarian
Received October 28, 2005; revised and accepted April 3, 2006. Reprint requests: Ülkü Bayar, M.D., Department of Obstetrics and Gynecology, Faculty of Medicine, Zonguldak Karaelmas University, 67600 Kozlu, Zonguldak, Turkey (FAX: 90-372-2610155; E-mail: ulkubayar@ yahoo.com).
0015-0282/06/$32.00 doi:10.1016/j.fertnstert.2006.04.026
hyperstimulation syndrome (OHSS) and multifetal pregnancy significantly are increased (6). Aromatase inhibitors originally were developed for the treatment of breast cancer. Aromatase is a cytochrome P-450 hemoprotein that catalyzes the rate-limiting step in estrogen synthesis, that is, the 3-hydroxylation step in the conversion of androstenedione and T to estrone and E2, respectively (7). Letrozole is a specific, reversible, nonsteroidal aromatase inhibitor that suppresses estrogen biosynthesis (8). Recent clinical evidence showed that it could be used as an alternative to CC in ovulation induction (9 –11). Also, the addition of letrozole to gonadotropins decreases gonadotropin doses and increases the number of the preovulatory follicles (12–14). It has been suggested that letrozole increases endogenous gonadotropin secretion, as seen with CC. However, unlike CC, letrozole does not cause a decrease in estrogen receptors (14). In this study, we aimed to investigate the role of letrozole as a first-line ovulation-induction agent and to compare the clinical parameters with those of CC in PCOS patients.
Fertility and Sterility姞 Vol. 86, No. 5, November 2006 Copyright ©2006 American Society for Reproductive Medicine, Published by Elsevier Inc.
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FIGURE 1 Flow diagram of progress through the phases of randomized trial.
vartis Pharma AG, Basel, Switzerland). The second group received CC (100 mg/d, Gonaphane; Organon, Santa Farma Ilac Sanayi, Istanbul, Turkey). Both treatments were administered on days 3 to 7 of the menstrual cycle. Patients were followed with follicular monitoring with transvaginal ultrasonography and with serial measurements of estradiol and LH starting on day 7 of the menstrual cycle. Follicular size was measured as mean diameter. Endometrial thickness was determined at the greatest diameter perpendicular to the midsagittal plane in the fundal region, including both layers of the endometrium. The hCG (10,000 IU, SC) was administered to trigger the ovulation when at least one mature follicle (ⱖ18 mm) developed, followed by timed intercourse. The same criteria were used for administration of hCG in both groups of patients. Serum -hCG was measured 5 days after the first missed menstrual period. The pregnancy rate was calculated with respect to a positive result on a serum -hCG of ⬎10 mIU/mL. Intra- and interassay coefficients of variation (CVs) of FSH, E2, and P were as follows: FSH (analytical sensitivity, 0.1 mIU/mL; intra-assay CV, 1.90%; and interassay CV, 2.11%), E2 (analytical sensitivity, 15 pg/mL; intra-assay CV, 2.50%; and interassay CV, 3.23%), and P (analytical sensitivity, 0.1 ng/mL; intra-assay CV, 1.13%; and interassay CV, 1.72%).
Bayar. Aromatase inhibitor in PCOS patients. Fertil Steril 2006.
MATERIALS AND METHODS During the study period of 2004 through 2005, 80 patients with PCOS who attended the outpatient clinics of the Infertility and Reproductive Medicine Unit of the Zonguldak Karaelmas University Hospital (Zonguldak, Turkey) participated in this study. The study was approved by the Institutional Ethics Committee of Karaelmas University (Fig. 1). In this prospective double-blind study, each patient’s treatment was determined by simple randomization, performed by a computer. Allocation concealment was achieved by using central consultation for treatment of eligible patients. Our study group consisted of anovulatory PCOS patients diagnosed by using the Rotterdam criteria (1). Tubal, peritoneal, and uterine causes of infertility were excluded by hysterosalpingography, laparoscopy, or transvaginal ultrasonography (LOGIQ 7 Scanner, GE Medical Systems, Milwaukee, WI). Specific endocrine abnormalities (Cushing’s disease, hypothyroidism, hyperthyroidism, congenital adrenal hyperplasia, and prolactinoma), male-factor infertility, and women with a body mass index of ⬎25 kg/m2 were excluded from the study. Eighty patients were randomized into two equal groups. The first group received letrozole (2.5 mg/d, Femara; No1448
Bayar et al.
Aromatase inhibitor in PCOS patients
The statistical package SPSS 11.5 for Windows (SPSS Inc., Chicago, IL) was used for statistical analyses. The 2 test and Fisher’s exact test were used to analyze the frequencies of nominal variables in cross-tables. Student’s t test and Mann-Whitney U test were used to compare parametric and nonparametric data of two groups, respectively. Type I error was set at 0.05. Sample-size determination was based on the difference between the median number of follicles sized ⬎15 mm and E2 concentration on hCG day. A sample size of 60 patients (30 patients in each group) was targeted to be able to detect a difference of at least one follicle or of 200 pmol/L between the two groups, with ␣ (type I error) set at 0.05 and 80% power. RESULTS The two groups were comparable regarding the baseline characteristics, including female age, basal FSH level, and duration of infertility (Table 1). Two patients in the letrozole group and four patients in the CC group were lost to follow-up during the study. Patients in the letrozole and CC groups had 99 and 95 cycles, respectively (Table 2). All patients were scheduled for timed intercourse. Ovulation occurred in 65.7% (65/99) of the cycles with letrozole and in 74.7% (71/95) of the cycles with CC (P⫽.17), respectively. The median E2 level on the day of hCG administration was significantly lower in the letrozole group (P⬍.001). Also, the median E2 level per follicle sized ⬎15 mm in diameter was significantly lower in the letrozole group (P⫽.002; Table 2). Vol. 86, No. 5, November 2006
TABLE 1 Demographic features and ovarian reserve of the letrozole- and CC-treated groups. Variable
Letrozole
CC
No. of patients 38 36 No. of cycles 2 (1–4) 3 (1–5) performed Female age (y) 32.2 ⫾ 3.9 30.6 ⫾ 4.0 Duration of 5 (1–10) 3 (1–11) infertility (y) Day 3 FSH (mIU/mL) 6 (2–10) 6 (3–11)
P .61 .09 .06 .9
Note: Data are given either as mean ⫾ SD or as median (range). Bayar. Aromatase inhibitor in PCOS patients. Fertil Steril 2006.
The median number of follicles ⬎15 mm in diameter on the day of hCG administration were significantly lower in the letrozole group (P⫽.015). The median endometrial thickness on hCG day in CC and letrozole groups were both 8 mm (P⫽.06, Table 2). However, endometrial thickness was ⬍5 mm in six cycles (6.1% [3 mm in one cycle and 4 mm in five cycles]) in the letrozole group, whereas it was ⱖ5 mm in all cycles in the CC group (P⫽.03). Pregnancy was achieved in nine (9.1%) of the letrozole cycles and in seven (7.4%) of the CC cycles (P⫽.66; Table 2). One abortion occurred in the letrozole-treated group; the remaining pregnancies reached term. No multifetal pregnancy was observed in either group. Patients did not report any significant side effect while taking letrozole. DISCUSSION Polycystic ovarian syndrome is a syndrome that is diagnosed with a specific criteria and exclusion of secondary causes of
anovulation and hyperandrogenism. Current recommendation for PCOS diagnosis includes any two of the following three criteria: [1] polycystic ovaries, [2] oligoovulation and anovulation, and/or [3] clinical or biochemical evidence of hyperandrogenism (1). Clomiphene citrate is the traditional first-line treatment in patients with chronic anovulation in PCOS, with a success rate of 30%– 40% (3). However, CC may compromise the success of treatment because of the antiestrogenic effect on the endometrium, substantial luteal-phase defect, implantation failure, and early pregnancy loss (15). Letrozole (4, 4=-[1H-1, 2, 4-triazol-1-ylmethylene]-bisbenzonitrile) is a type 2, third-generation, cytochrome P-450 –linked aromatase inhibitor that reversibly suppresses estrogen biosynthesis. Letrozole has been used in the treatment of postmenopausal breast and endometrial cancer (8, 16). Estrogen synthesis is suppressed in ovaries and brain (14), which may be responsible for a robust increase in FSH release and subsequent follicle stimulation and ovulation in PCOS patients. In addition, negative-feedback inhibition of FSH with inhibin is not affected by aromatase inhibition (17). Limited FSH response can be a protective factor for multiple ovulation and OHSS. Also, local effects in ovaries were proposed for follicular sensitivity to FSH (14). Letrozole prevents the conversion of androgens to estrogen (18) and causes increasing levels of LH and T (19). Recent data support that T was found to augment follicular FSH receptor expression in primates, suggesting that androgens promote follicular growth and estrogen biosynthesis indirectly by amplifying FSH effects (20, 21). This results in increased secretion of gonadotropins. The suggested mechanism of action is the increased secretion of FSH, and this may be a local effect of increasing androgen concentration and sensitivity of the ovaries to FSH (20 –23). Actually, PCOS patients have a relative aromatase defi-
TABLE 2 Ovulation induction outcome of the letrozole and CC groups. Variable
Letrozole (n ⴝ 99 cycles)
CC (n ⴝ 95 cycles)
P
No. of follicles sized ⬎15 mm in diameter on the day of hCG 1 (0–4) 1 (0–5) .015 Endometrial thickness on the day of hCG (mm) 8 (4–15) 8 (5–15) .06 189 (18–1,531) 386 (27–6,190) ⬍.001 E2 level on the day of hCG (pg/mL) E2 per follicle sized ⬎15 mm in diameter on the day of 160 (18–808) 281 (27–2,615) ⬍.001 hCG (pg/mL) Overall ovulation rate, n (%) 65/99 (65.7) 71/95 (74.7) .17 Pregnancy rate per cycle, n (%) 9/99 (9.1) 7/95 (7.4) .66 Delivery rate per cycle, n (%) 8/99 (8.1) 7/95 (7.4) .92 Note: Values are expressed either as n (%) or as median (minimum–maximum). Bayar. Aromatase inhibitor in PCOS patients. Fertil Steril 2006.
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ciency in the ovary, leading to increased androgens (24). Androgens, by means of increasing FSH receptors, make these PCOS ovaries excessively sensitive to an increase in FSH. Both exogenous administration of gonadotropins (hence the high risk of OHSS) and endogenous increases in FSH can result in decreased central estrogen feedback induced by aromatase inhibition. Consequently, aromatase inhibitors may cause a relatively small rise in FSH, leading to unifollicular or low multifollicular development, thus avoiding the occurrence of OHSS. Experience with letrozole in anovulatory infertility is limited (9, 10). Mitwally and Casper (9) have reported the use of letrozole in 12 patients with PCOS. In the PCOS group, ovulation occurred in nine patients (75%), and pregnancy was achieved in three (25%) (9). Al-Omari et al. (10) compared two types of aromatase inhibitors: letrozole and anastrazole efficiency on ovulation and conception in infertile, CC-resistant women with PCOS. They reported that oral administration of aromatase inhibitors was effective with a higher rate of success with letrozole than with anastrozole. The teratogenic potential of aromatase inhibitor was shown in animal studies (25). However, compared with other ovulationinduction agents, Mitwally et al. (26) reported similar miscarriage, ectopic-pregnancy, and cycle-cancellation rates as well as pregnancy outcome in letrozole-treated patients. Our results were compatible with these data in that we observe one abortion in the letrozole group. Letrozole’s short halflife (2 d) (27) and usage for short period of time and in small doses during the follicular phase of the menstrual cycle prevents drug exposure during organogenesis (28). In this study, we compared letrozole with CC as a first-line therapeutic agent for ovulation induction in patients with PCOS. The number of follicles ⬎15 mm in diameter on the day of hCG, E2 level, and E2 level per follicle ⬎15 mm were significantly lower in the letrozole group. However, despite this significant difference, the pregnancy rates of the two groups were comparable. Therefore, we could conclude that letrozole should be considered as a novel therapeutic agent for ovulation induction that acts on different pathways. In conclusion, in this study, we showed that letrozole is as effective as CC in PCOS patients who previously have not been treated with other ovulation-induction agents. The use of letrozole as a first-line ovulation-induction agent in PCOS patients may be favored because of beneficial effects in terms of fewer mature follicles (decrease in multiple-pregnancy rate) and a decreased risk of OHSS. REFERENCES 1. The Rotterdam ESHRE/ASRM-sponsored PCOS Consensus Workshop Group. Revised 2003 consensus on diagnostic criteria and long-term health risks related to polycystic ovary syndrome. Fertil Steril 2004; 81:19 –25. 2. Hammond MG. Monitoring techniques for improved pregnancy rates during clomiphene ovulation induction. Fertil Steril 1984;42:499 –509.
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3. European Society for Human Reproduction and Embryology. Female infertility: treatment options for complicated cases. The ESHRE Capri Workshop. Hum Reprod 1997;12:1191– 6. 4. DiMarzo SJ, Kennedy JF, Young PE, Hebert SA, Rosenberg DC, Villanueva B. Effect of controlled ovarian hyperstimulation on pregnancy rates after intrauterine insemination. Am J Obstet Gynecol 1992;166:1607–12. 5. Dodson WC, Whitesides DB, Hughes CL Jr, Easley HA 3rd, Haney AF. Superovulation with intrauterine insemination in the treatment of infertility: a possible alternative to gamete intrafallopian transfer and in vitro fertilization. Fertil Steril 1987;48:441–5. 6. Hamilton-Fairley D, Franks S. Common problems in induction of ovulation. Baillieres Clin Obstet Gynaecol 1990;4:609 –25. 7. Brodie A, Lu Q, Liu Y, Long B. Aromatase inhibitors and their antitumor effects in model systems. Endocr Relat Cancer 1999;6:205– 10. 8. Buzdar AU. A summary of second-line randomized studies of aromatase inhibitors. J Steroid Biochem Mol Biol 2001;79:109 –14. 9. Mitwally MF, Casper RF. Use of an aromatase inhibitor for induction of ovulation in patients with an inadequate response to clomiphene citrate. Fertil Steril 2001;75:305–9. 10. Al-Omari WR, Sulaiman WR, Al-Hadithi N. Comparison of two aromatase inhibitors in women with clomiphene-resistant polycystic ovary syndrome. Int J Gynaecol Obstet 2004;85:289 –91. 11. Al-Fozan H, Al-Khadouri M, Tan SL, Tulandi T. A randomized trial of letrozole versus clomiphene citrate in women undergoing superovulation. Fertil Steril 2004;82:1561–3. 12. Healey S, Tan SL, Tulandi T, Biljan MM. Effects of letrozole on superovulation with gonadotropins in women undergoing intrauterine insemination. Fertil Steril 2003;80:1325–9. 13. Mitwally MF, Casper RF. Aromatase inhibition improves ovarian response to follicle-stimulating hormone in poor responders. Fertil Steril 2002;77:776 – 80. 14. Mitwally MF, Casper RF. Aromatase inhibition reduces the dose of gonadotropin required for controlled ovarian hyperstimulation. J Soc Gynecol Investig 2004;11:406 –15. 15. Jennings JC, Moreland K, Peterson CM. In vitro fertilisation. A review of drug therapy and clinical management. Drugs 1996;52:313– 43. 16. Berstein L, Maximov S, Gershfeld E, Meshkova I, Gamajunova V, Tsyrlina E, et al. Neoadjuvant therapy of endometrial cancer with the aromatase inhibitor letrozole: endocrine and clinical effects. Eur J Obstet Gynecol Reprod Biol 2002;105:161–5. 17. Roberts VJ, Barth S, el-Roeiy A, Yen SS. Expression of inhibin/activin system messenger ribonucleic acids and proteins in ovarian follicles from women with polycystic ovarian syndrome. J Clin Endocrinol Metab 1994;79:1434 –9. 18. Brodie AM, Njar VC. Aromatase inhibitors and breast cancer. Semin Oncol 1996;23:10 –20. 19. Kafali H, Iriadam M, Ozardali I, Demir N. Letrozole-induced polycystic ovaries in the rat: a new model for cystic ovarian disease. Arch Med Res 2004;35:103– 8. 20. Weil SJ, Vendola K, Zhou J, Adesanya OO, Wang J, Okafor J, et al. Androgen receptor gene expression in the primate ovary: cellular localization, regulation, and functional correlations. J Clin Endocrinol Metab 1998;83:2479 – 85. 21. Vendola KA, Zhou J, Adesanya OO, Weil SJ, Bondy CA. Androgens stimulate early stages of follicular growth in the primate ovary. J Clin Invest 1998;101:2622–9. 22. Weil S, Vendola K, Zhou J, Bondy CA. Androgen and folliclestimulating hormone interactions in primate ovarian follicle development. J Clin Endocrinol Metab 1999;84:2951– 6. 23. Shetty G, Krishnamurthy H, Krishnamurthy HN, Bhatnagar S, Moudgal RN. Effect of estrogen deprivation on the reproductive physiology of male and female primates. J Steroid Biochem Mol Biol 1997;61:157– 66. 24. Jakimiuk AJ, Weitsman SR, Brzechffa PR, Magoffin DA. Aromatase mRNA expression in individual follicles from polycystic ovaries. Mol Hum Reprod 1998;4:1– 8.
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25. Beltrame D, di Salle E, Giavini E, Gunnarsson K, Brughera M. Reproductive toxicity of exemestane, an antitumoral aromatase inactivator, in rats and rabbits. Reprod Toxicol 2001;15:195–213. 26. Mitwally MF, Biljan MM, Casper RF. Pregnancy outcome after the use of an aromatase inhibitor for ovarian stimulation. Am J Obstet Gynecol 2005;192:381– 6.
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27. Sioufi A, Sandrenan N, Godbillon J, Trunet P, Czendlik C, Howald H, et al. Comparative bioavailability of letrozole under fed and fasting conditions in 12 healthy subjects after a 2.5 mg single oral administration. Biopharm Drug Dispos 1997;18:489 –97. 28. Tiboni GM. Aromatase inhibitors and teratogenesis. Fertil Steril 2004; 81:1158 –9.
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Objective: To compare the use of an aromatase inhibitor (letrozole) with the use of clomiphene citrate (CC). Design: Prospective randomized study. Setting: An infertility clinic in a university hospital. Patient(s): Seventy-four consecutive infertile patients with polycystic ovary syndrome were recruited. Thirtyeight patients were randomized to the letrozole group (99 cycles), and the remaining patients were recruited to the CC group (95 cycles). Intervention(s): The aromatase inhibitor letrozole (2.5 mg/d) and CC (100 mg/d) were administered orally on days 3–7 of menses. Main Outcome Measure(s): Number of follicles, endometrial thickness, E2 levels on hCG day, and pregnancy rates among both groups. Result(s): Ovulation occurred in 65.7% (65/99) of letrozole cycles and in 74.7% (71/95) of CC cycles. The median (minimum–maximum) number of follicles sized ⬎15 mm in diameter on the day of hCG administration were 1 (0 – 4) and 1 (0 –5) in the letrozole and CC groups, respectively. On the day of hCG administration, median serum E2 concentrations in the letrozole and CC groups were statistically significantly different: 189 pg/mL (18 –1,581 pg/mL) and 386 pg/mL (27– 6,190 pg/mL), respectively. The median serum E2 concentrations per follicle sized ⬎15 mm in diameter on the day of hCG also statistically significantly differed between the letrozole and CC groups: 160 pg/mL (18 – 808 pg/mL) and 281 pg/mL (27–2,615 pg/mL), respectively. The median endometrial thickness on the day of hCG did not significantly differ between the CC and letrozole groups; it was 8 mm. Pregnancy was achieved in nine cycles (9.1%) of the letrozole group and in seven cycles (7.4%) of the CC group, which also was not a statistically significant difference. Conclusion(s): The aromatase inhibitor letrozole may be an acceptable alternative to CC as an ovulation-induction drug in patients with PCOS. (Fertil Steril威 2006;86:1447–51. ©2006 by American Society for Reproductive Medicine.) Key Words: Letrozole, clomiphene citrate, PCOS, ovulation induction
Polycystic ovarian syndrome (PCOS) is characterized by chronic anovulation, hyperandrogenism, and polycystic ovaries. Although considerable progress has been made toward a better understanding of pathogenesis, the exact cause (or causes) still is unknown (1). Clomiphene citrate (CC) frequently is used for ovulation induction and is highly effective in initiating ovulation in patients with PCOS (2). However, despite a 75%– 80% ovulation rate with CC use, the cumulative pregnancy rate after 6 months of treatment is only 40%– 45% (3). In patients who do not respond to treatment after four to six cycles of CC, gonadotropins usually are administered for an additional six cycles (4, 5). In PCOS patients, as a result of the increased sensitivity of ovaries to gonadotropin stimulation, the risks of ovarian
Received October 28, 2005; revised and accepted April 3, 2006. Reprint requests: Ülkü Bayar, M.D., Department of Obstetrics and Gynecology, Faculty of Medicine, Zonguldak Karaelmas University, 67600 Kozlu, Zonguldak, Turkey (FAX: 90-372-2610155; E-mail: ulkubayar@ yahoo.com).
0015-0282/06/$32.00 doi:10.1016/j.fertnstert.2006.04.026
hyperstimulation syndrome (OHSS) and multifetal pregnancy significantly are increased (6). Aromatase inhibitors originally were developed for the treatment of breast cancer. Aromatase is a cytochrome P-450 hemoprotein that catalyzes the rate-limiting step in estrogen synthesis, that is, the 3-hydroxylation step in the conversion of androstenedione and T to estrone and E2, respectively (7). Letrozole is a specific, reversible, nonsteroidal aromatase inhibitor that suppresses estrogen biosynthesis (8). Recent clinical evidence showed that it could be used as an alternative to CC in ovulation induction (9 –11). Also, the addition of letrozole to gonadotropins decreases gonadotropin doses and increases the number of the preovulatory follicles (12–14). It has been suggested that letrozole increases endogenous gonadotropin secretion, as seen with CC. However, unlike CC, letrozole does not cause a decrease in estrogen receptors (14). In this study, we aimed to investigate the role of letrozole as a first-line ovulation-induction agent and to compare the clinical parameters with those of CC in PCOS patients.
Fertility and Sterility姞 Vol. 86, No. 5, November 2006 Copyright ©2006 American Society for Reproductive Medicine, Published by Elsevier Inc.
1447
FIGURE 1 Flow diagram of progress through the phases of randomized trial.
vartis Pharma AG, Basel, Switzerland). The second group received CC (100 mg/d, Gonaphane; Organon, Santa Farma Ilac Sanayi, Istanbul, Turkey). Both treatments were administered on days 3 to 7 of the menstrual cycle. Patients were followed with follicular monitoring with transvaginal ultrasonography and with serial measurements of estradiol and LH starting on day 7 of the menstrual cycle. Follicular size was measured as mean diameter. Endometrial thickness was determined at the greatest diameter perpendicular to the midsagittal plane in the fundal region, including both layers of the endometrium. The hCG (10,000 IU, SC) was administered to trigger the ovulation when at least one mature follicle (ⱖ18 mm) developed, followed by timed intercourse. The same criteria were used for administration of hCG in both groups of patients. Serum -hCG was measured 5 days after the first missed menstrual period. The pregnancy rate was calculated with respect to a positive result on a serum -hCG of ⬎10 mIU/mL. Intra- and interassay coefficients of variation (CVs) of FSH, E2, and P were as follows: FSH (analytical sensitivity, 0.1 mIU/mL; intra-assay CV, 1.90%; and interassay CV, 2.11%), E2 (analytical sensitivity, 15 pg/mL; intra-assay CV, 2.50%; and interassay CV, 3.23%), and P (analytical sensitivity, 0.1 ng/mL; intra-assay CV, 1.13%; and interassay CV, 1.72%).
Bayar. Aromatase inhibitor in PCOS patients. Fertil Steril 2006.
MATERIALS AND METHODS During the study period of 2004 through 2005, 80 patients with PCOS who attended the outpatient clinics of the Infertility and Reproductive Medicine Unit of the Zonguldak Karaelmas University Hospital (Zonguldak, Turkey) participated in this study. The study was approved by the Institutional Ethics Committee of Karaelmas University (Fig. 1). In this prospective double-blind study, each patient’s treatment was determined by simple randomization, performed by a computer. Allocation concealment was achieved by using central consultation for treatment of eligible patients. Our study group consisted of anovulatory PCOS patients diagnosed by using the Rotterdam criteria (1). Tubal, peritoneal, and uterine causes of infertility were excluded by hysterosalpingography, laparoscopy, or transvaginal ultrasonography (LOGIQ 7 Scanner, GE Medical Systems, Milwaukee, WI). Specific endocrine abnormalities (Cushing’s disease, hypothyroidism, hyperthyroidism, congenital adrenal hyperplasia, and prolactinoma), male-factor infertility, and women with a body mass index of ⬎25 kg/m2 were excluded from the study. Eighty patients were randomized into two equal groups. The first group received letrozole (2.5 mg/d, Femara; No1448
Bayar et al.
Aromatase inhibitor in PCOS patients
The statistical package SPSS 11.5 for Windows (SPSS Inc., Chicago, IL) was used for statistical analyses. The 2 test and Fisher’s exact test were used to analyze the frequencies of nominal variables in cross-tables. Student’s t test and Mann-Whitney U test were used to compare parametric and nonparametric data of two groups, respectively. Type I error was set at 0.05. Sample-size determination was based on the difference between the median number of follicles sized ⬎15 mm and E2 concentration on hCG day. A sample size of 60 patients (30 patients in each group) was targeted to be able to detect a difference of at least one follicle or of 200 pmol/L between the two groups, with ␣ (type I error) set at 0.05 and 80% power. RESULTS The two groups were comparable regarding the baseline characteristics, including female age, basal FSH level, and duration of infertility (Table 1). Two patients in the letrozole group and four patients in the CC group were lost to follow-up during the study. Patients in the letrozole and CC groups had 99 and 95 cycles, respectively (Table 2). All patients were scheduled for timed intercourse. Ovulation occurred in 65.7% (65/99) of the cycles with letrozole and in 74.7% (71/95) of the cycles with CC (P⫽.17), respectively. The median E2 level on the day of hCG administration was significantly lower in the letrozole group (P⬍.001). Also, the median E2 level per follicle sized ⬎15 mm in diameter was significantly lower in the letrozole group (P⫽.002; Table 2). Vol. 86, No. 5, November 2006
TABLE 1 Demographic features and ovarian reserve of the letrozole- and CC-treated groups. Variable
Letrozole
CC
No. of patients 38 36 No. of cycles 2 (1–4) 3 (1–5) performed Female age (y) 32.2 ⫾ 3.9 30.6 ⫾ 4.0 Duration of 5 (1–10) 3 (1–11) infertility (y) Day 3 FSH (mIU/mL) 6 (2–10) 6 (3–11)
P .61 .09 .06 .9
Note: Data are given either as mean ⫾ SD or as median (range). Bayar. Aromatase inhibitor in PCOS patients. Fertil Steril 2006.
The median number of follicles ⬎15 mm in diameter on the day of hCG administration were significantly lower in the letrozole group (P⫽.015). The median endometrial thickness on hCG day in CC and letrozole groups were both 8 mm (P⫽.06, Table 2). However, endometrial thickness was ⬍5 mm in six cycles (6.1% [3 mm in one cycle and 4 mm in five cycles]) in the letrozole group, whereas it was ⱖ5 mm in all cycles in the CC group (P⫽.03). Pregnancy was achieved in nine (9.1%) of the letrozole cycles and in seven (7.4%) of the CC cycles (P⫽.66; Table 2). One abortion occurred in the letrozole-treated group; the remaining pregnancies reached term. No multifetal pregnancy was observed in either group. Patients did not report any significant side effect while taking letrozole. DISCUSSION Polycystic ovarian syndrome is a syndrome that is diagnosed with a specific criteria and exclusion of secondary causes of
anovulation and hyperandrogenism. Current recommendation for PCOS diagnosis includes any two of the following three criteria: [1] polycystic ovaries, [2] oligoovulation and anovulation, and/or [3] clinical or biochemical evidence of hyperandrogenism (1). Clomiphene citrate is the traditional first-line treatment in patients with chronic anovulation in PCOS, with a success rate of 30%– 40% (3). However, CC may compromise the success of treatment because of the antiestrogenic effect on the endometrium, substantial luteal-phase defect, implantation failure, and early pregnancy loss (15). Letrozole (4, 4=-[1H-1, 2, 4-triazol-1-ylmethylene]-bisbenzonitrile) is a type 2, third-generation, cytochrome P-450 –linked aromatase inhibitor that reversibly suppresses estrogen biosynthesis. Letrozole has been used in the treatment of postmenopausal breast and endometrial cancer (8, 16). Estrogen synthesis is suppressed in ovaries and brain (14), which may be responsible for a robust increase in FSH release and subsequent follicle stimulation and ovulation in PCOS patients. In addition, negative-feedback inhibition of FSH with inhibin is not affected by aromatase inhibition (17). Limited FSH response can be a protective factor for multiple ovulation and OHSS. Also, local effects in ovaries were proposed for follicular sensitivity to FSH (14). Letrozole prevents the conversion of androgens to estrogen (18) and causes increasing levels of LH and T (19). Recent data support that T was found to augment follicular FSH receptor expression in primates, suggesting that androgens promote follicular growth and estrogen biosynthesis indirectly by amplifying FSH effects (20, 21). This results in increased secretion of gonadotropins. The suggested mechanism of action is the increased secretion of FSH, and this may be a local effect of increasing androgen concentration and sensitivity of the ovaries to FSH (20 –23). Actually, PCOS patients have a relative aromatase defi-
TABLE 2 Ovulation induction outcome of the letrozole and CC groups. Variable
Letrozole (n ⴝ 99 cycles)
CC (n ⴝ 95 cycles)
P
No. of follicles sized ⬎15 mm in diameter on the day of hCG 1 (0–4) 1 (0–5) .015 Endometrial thickness on the day of hCG (mm) 8 (4–15) 8 (5–15) .06 189 (18–1,531) 386 (27–6,190) ⬍.001 E2 level on the day of hCG (pg/mL) E2 per follicle sized ⬎15 mm in diameter on the day of 160 (18–808) 281 (27–2,615) ⬍.001 hCG (pg/mL) Overall ovulation rate, n (%) 65/99 (65.7) 71/95 (74.7) .17 Pregnancy rate per cycle, n (%) 9/99 (9.1) 7/95 (7.4) .66 Delivery rate per cycle, n (%) 8/99 (8.1) 7/95 (7.4) .92 Note: Values are expressed either as n (%) or as median (minimum–maximum). Bayar. Aromatase inhibitor in PCOS patients. Fertil Steril 2006.
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ciency in the ovary, leading to increased androgens (24). Androgens, by means of increasing FSH receptors, make these PCOS ovaries excessively sensitive to an increase in FSH. Both exogenous administration of gonadotropins (hence the high risk of OHSS) and endogenous increases in FSH can result in decreased central estrogen feedback induced by aromatase inhibition. Consequently, aromatase inhibitors may cause a relatively small rise in FSH, leading to unifollicular or low multifollicular development, thus avoiding the occurrence of OHSS. Experience with letrozole in anovulatory infertility is limited (9, 10). Mitwally and Casper (9) have reported the use of letrozole in 12 patients with PCOS. In the PCOS group, ovulation occurred in nine patients (75%), and pregnancy was achieved in three (25%) (9). Al-Omari et al. (10) compared two types of aromatase inhibitors: letrozole and anastrazole efficiency on ovulation and conception in infertile, CC-resistant women with PCOS. They reported that oral administration of aromatase inhibitors was effective with a higher rate of success with letrozole than with anastrozole. The teratogenic potential of aromatase inhibitor was shown in animal studies (25). However, compared with other ovulationinduction agents, Mitwally et al. (26) reported similar miscarriage, ectopic-pregnancy, and cycle-cancellation rates as well as pregnancy outcome in letrozole-treated patients. Our results were compatible with these data in that we observe one abortion in the letrozole group. Letrozole’s short halflife (2 d) (27) and usage for short period of time and in small doses during the follicular phase of the menstrual cycle prevents drug exposure during organogenesis (28). In this study, we compared letrozole with CC as a first-line therapeutic agent for ovulation induction in patients with PCOS. The number of follicles ⬎15 mm in diameter on the day of hCG, E2 level, and E2 level per follicle ⬎15 mm were significantly lower in the letrozole group. However, despite this significant difference, the pregnancy rates of the two groups were comparable. Therefore, we could conclude that letrozole should be considered as a novel therapeutic agent for ovulation induction that acts on different pathways. In conclusion, in this study, we showed that letrozole is as effective as CC in PCOS patients who previously have not been treated with other ovulation-induction agents. The use of letrozole as a first-line ovulation-induction agent in PCOS patients may be favored because of beneficial effects in terms of fewer mature follicles (decrease in multiple-pregnancy rate) and a decreased risk of OHSS. REFERENCES 1. The Rotterdam ESHRE/ASRM-sponsored PCOS Consensus Workshop Group. Revised 2003 consensus on diagnostic criteria and long-term health risks related to polycystic ovary syndrome. Fertil Steril 2004; 81:19 –25. 2. Hammond MG. Monitoring techniques for improved pregnancy rates during clomiphene ovulation induction. Fertil Steril 1984;42:499 –509.
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27. Sioufi A, Sandrenan N, Godbillon J, Trunet P, Czendlik C, Howald H, et al. Comparative bioavailability of letrozole under fed and fasting conditions in 12 healthy subjects after a 2.5 mg single oral administration. Biopharm Drug Dispos 1997;18:489 –97. 28. Tiboni GM. Aromatase inhibitors and teratogenesis. Fertil Steril 2004; 81:1158 –9.
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