Anastrozole, also known as Arimidex, is a drug prescribed for the treatment of breast cancer in women who have been through the menopause and those with estrogen-receptor-positive breast cancer. This anti-estrogen drug may also be used as a preventive method to reduce the risk of breast cancer in women who have a family history of the disease. Men with breast cancer may also be treated with anastrozole.
How does Anastrozole Work?
Anastrozole belongs to a class of medications called nonsteroidal aromatase inhibitors. It works by inhibiting the production of the hormone estrogen by blocking aromatase, an enzyme which converts the hormone androgen into small amounts of estrogen. This mechanism results in lesser estrogen available to stimulate the growth of breast cancer cells.
What is the Effect of Unbalanced Aromatase?
Unbalanced aromatase is associated with fluctuations in estradiol, the main form of estrogen. Although estradiol production is a common problem in women, men also need to maintain balanced levels of this hormone. Since men do not have ovaries (where large amounts of estradiol is produced), estradiol in men is produced in fat cells, liver, and testicles through a complex process that requires aromatase. For optimal health, men and women should have an estradiol level of 18-30 picograms per milliliter (pg/mL).
As men age, aromatase activity in their bodies dramatically increases, resulting in higher estradiol and lower testosterone levels. Aside from old age, men on testosterone replacement therapy (TRT) can also experience an increase in estradiol and dihydrotestosterone (stronger version of testosterone). Elevated levels of estradiol can cause unpleasant symptoms in men such as:
- Benign prostatic hyperplasia (BPH)
- Decreased muscle mass
- Emotional disturbances such as anxiety and depression
- Enlarged breasts (gynecomastia)
- Increased abdominal fat
- Sexual dysfunction (decreased libido and erectile dysfunction)
- Type 2 diabetes
On the other hand, men can also produce too little aromatase, resulting in low estrogen levels. This causes serious health problems such as:
- Bone problems
- Depression and anxiety
- Erectile dysfunction
- Increased body fat
Overall Health Benefits of Anastrozole
- Combats cancer [1-22]
- Increases pregnancy rate [23-32]
- Improves sperm quality [33-41]
- Improves body composition [42-44]
Proven Health Benefits of Anastrozole
Anastrozole is known as a potent anti-cancer drug. Strong scientific evidence shows that this nonsteroidal aromatase inhibitor is effective against various types of cancer:
- In postmenopausal women with advanced breast cancer, significant survival advantage and improvement in quality of life parameters were observed in subjects treated with anastrozole at 1 mg/day. 
- In postmenopausal women with early-stage breast cancer, treatment with anastrozole beyond 5 years further reduced the risk of breast cancer recurrence. 
- Phase III clinical trials have also demonstrated that anastrozole dramatically delays tumor progression compared with tamoxifen, an anti-estrogen drug, in postmenopausal women with advanced estrogen-receptor-positive breast cancer. 
- Anastrozole treatment at doses of 1 and 10 mg once daily have also been found to be effective in the treatment of postmenopausal women with advanced breast cancer who benefited from tamoxifen treatment. 
- Long-term follow up data from the ATAC (Anastrozole, Tamoxifen Alone or in Combination) trial confirmed the efficacy of anastrozole in the treatment of hormone-sensitive early breast cancer in postmenopausal women. 
- A study found that anastrozole has been used in the chemoprevention and treatment of early-stage breast cancer in postmenopausal women. 
- A cell study found that treatment of tumor cells with anastrozole led to significant suppression of tumor cell growth. 
- Studies found that anti-estrogen treatment is associated with a significant reduction in lung cancer mortality. [8-9]
- In postmenopausal women with advanced non-small cell lung cancer, anastrozole slowed the time to when the cancer progresses. 
- In a postmenopausal woman with advanced breast cancer which spread to the lungs, anastrozole treatment resulted in marked regression of the lung tumor. 
- In an animal model of lung cancer, anastrozole combined with ibuprofen showed enhanced anti-tumor effects. [12-13]
- A cell study found that anastrozole induced growth suppression and cell cycle arrest of breast cancer cells. 
- A 2017 study published in Saudi Medical Journal found that anastrozole showed anti-cancer activities against breast, liver, and prostate cancer cells in a dose-dependent manner. 
- In women who took anastrozole 1 mg per day for 5 years, a 49% reduction in breast cancer was observed. 
- In postmenopausal women, anastrozole has been found to have a more favorable overall risk-benefit profile and lower recurrence rate of breast cancer than tamoxifen. 
- In postmenopausal women with breast cancer, treatment with anastrozole at 1 mg or 10 mg once daily for 28 days improved symptoms by reducing estrogen levels. 
- The International Breast Cancer Intervention Study II (IBIS-II) trial found that anastrozole can help reduce the risk of breast cancer in postmenopausal women with an increased risk of cancer. 
- A review of several clinical trials found that anastrozole have superior efficacy than tamoxifen in the treatment of early breast cancer. 
- In postmenopausal women who are at increased risk for breast cancer, treatment with anastrozole at 1 mg/day in addition to chemotherapeutic drugs has been recommended as the standard therapy. 
- When combined with testosterone therapy, anastrozole significantly reduced the growth and multiplication of human breast cancer cells. 
Increases Pregnancy Rate
High-quality studies assessing the benefits of anastrozole on women fertility have shown that this nonsteroidal aromatase inhibitor can induce ovulation and increase the chances of getting pregnant:
- In women with polycystic ovarian syndrome who are resistant to the fertility medication clomiphene, anastrozole induced ovulation and is associated with 15.1% pregnancy rate. 
- A 2013 study published in the Journal of Clinical Endocrinology & Metabolism found that anastrozole is effective at inducing ovulation in patients with polycystic ovarian syndrome and unexplained infertility. 
- Studies found that women treated with anastrozole had higher pregnancy rate compared with subjects who received clomiphene citrate. [25-27]
- In women with endometriosis-associated infertility, anastrozole increased pregnancy rate by 45% via inhibition of the growth of endometriotic cells. [28-29]
- A study showed that anastrozole does not only increase pregnancy rate in women with endometriosis but it also helps relieve unpleasant symptoms such as pain and bone problems. 
- In infertile women, treatment with 1 mg of anastrozole daily resulted in favorable pregnancy outcomes. 
- In clomiphene-resistant women with polycystic ovarian syndrome, anastrozole increased ovulation and pregnancy rate. 
Improves Sperm Quality
In men, anastrozole can be considered as a therapeutic option for infertility. A great deal of evidence suggests that this drug has the capacity to improve various sperm parameters:
- In infertile men with low sperm count, anastrozole treatment resulted in improvement in sperm concentration, motility (ability of sperm to move and reach the egg), and structure. 
- A study found that anastrozole can treat male infertility by raising testosterone levels. 
- A 2018 study published in BJU International found that combination therapy with anastrozole and clomiphene citrate is a safe and effective alternative for subfertile men with elevated estradiol level or low testosterone:estradiol ratio. 
- In men with low sperm count, semen analysis before and during anastrozole treatment found an increase in semen volume, sperm concentration, and motility index. 
- In men with low testosterone levels, treatment with 1 mg anastrozole daily significantly improved sperm parameters. 
- A 2012 study published in Fertility and Sterility found that treatment with 1 mg anastrozole orally every day for 6 months improved both hormonal and semen parameters in men with abnormally low sperm count. 
- A study found anastrozole (1 mg once daily) can treat male infertility by increasing the production of mature sperm cells (spermatogenesis). 
- In men with infertility secondary to morbid obesity, treatment with anastrozole normalized blood testosterone levels and spermatogenesis. 
- In men with low sperm count and men without sperm, anastrozole treatment resulted in higher success rate of in vitro fertilization. [40-41]
Improves Body Composition
Evidence suggests that anastrozole may exert beneficial effects in people with obesity as well as those with muscle wasting through increasing lean muscle mass:
- In women with breast cancer who were undergoing chemotherapy, anastrozole treatment resulted in an increase in lean body mass and free testosterone levels. 
- In patients with morbid obesity, anastrozole and other aromatase inhibitors reversed the deposition of abdominal fat. 
- In animal models, combination treatment of aromatase inhibitors and testosterone led to a significant decrease in body fat mass. 
- Wiseman LR, Adkins JC. Anastrozole. A review of its use in the management of postmenopausal women with advanced breast cancer. Drugs Aging. 1998;13(4):321-32.
- Sanford M, Plosker GL. Anastrozole: a review of its use in postmenopausal women with early-stage breast cancer. Drugs. 2008;68(9):1319-40.
- Mokbel K. Focus on anastrozole and breast cancer. Curr Med Res Opin. 2003;19(8):683-8.
- Buzdar A, Jonat W, Howell A, et al. Anastrozole, a potent and selective aromatase inhibitor, versus megestrol acetate in postmenopausal women with advanced breast cancer: results of overview analysis of two phase III trials. Arimidex Study Group. J Clin Oncol. 1996;14(7):2000-11.
- Gangadhara S, Bertelli G. Long-term efficacy and safety of anastrozole for adjuvant treatment of early breast cancer in postmenopausal women. Ther Clin Risk Manag. 2009;5(4):291–300. doi:10.2147/tcrm.s3856.
- Barros-oliveira MDC, Costa-silva DR, Andrade DB, et al. Use of anastrozole in the chemoprevention and treatment of breast cancer: A literature review. Rev Assoc Med Bras (1992). 2017;63(4):371-378.
- Weinberg OK, Marquez-garban DC, Fishbein MC, et al. Aromatase inhibitors in human lung cancer therapy. Cancer Res. 2005;65(24):11287-91.
- Burns TF, Stabile LP. Targeting the estrogen pathway for the treatment and prevention of lung cancer. Lung Cancer Manag. 2014;3(1):43–52. doi:10.2217/lmt.13.67.
- Lother SA, Harding GA, Musto G, Navaratnam S, Pitz MW. Antiestrogen use and survival of women with non-small cell lung cancer in Manitoba, Canada. Horm Cancer. 2013;4(5):270–276.
- Available from https://clinicaltrials.gov/ct2/show/NCT00932152.
- Sakurai T, Oura S, Kinoshita T, et al. [Advanced breast cancer with lung and pleural metastases responsive to anastrozole–a case report]. Gan To Kagaku Ryoho. 2002;29(9):1607-10.
- Young PA, Pietras RJ. Aromatase inhibitors combined with aspirin to prevent lung cancer in preclinical models. Transl Lung Cancer Res. 2018;7(Suppl 4):S373–S376. doi:10.21037/tlcr.2018.09.17.
- Stabile LP, Farooqui M, Kanterewicz B, et al. Preclinical Evidence for Combined Use of Aromatase Inhibitors and NSAIDs as Preventive Agents of Tobacco-Induced Lung Cancer. J Thorac Oncol. 2018;13(3):399-412.
- Thiantanawat A, Long BJ, Brodie AM. Signaling pathways of apoptosis activated by aromatase inhibitors and antiestrogens. Cancer Res. 2003;63(22):8037-50.
- Hassan F, El-Hiti GA, Abd-Allateef M, Yousif E. Cytotoxicity anticancer activities of anastrozole against breast, liver hepatocellular, and prostate cancer cells. Saudi Med J. 2017;38(4):359–365. doi:10.15537/smj.2017.4.17061.
- Cuzick J, Sestak I, Forbes JF, Dowsett M, Cawthorn S, Mansel RE, Loibl S, Bonanni B, Evans DG, Howell A; IBIS-II investigators. Use of anastrozole for breast cancer prevention (IBIS-II): long-term results of a randomised controlled trial. Lancet. 2020 Jan 11;395(10218):117-122. doi: 10.1016/S0140-6736(19)32955-1. Epub 2019 Dec 12. Erratum in: Lancet. 2020 Feb 15;395(10223):496. PMID: 31839281; PMCID: PMC6961114.
- Arimidex, Tamoxifen, Alone or in Combination Trialists’ Group, Buzdar A, Howell A, Cuzick J, Wale C, Distler W, Hoctin-Boes G, Houghton J, Locker GY, Nabholtz JM. Comprehensive side-effect profile of anastrozole and tamoxifen as adjuvant treatment for early-stage breast cancer: long-term safety analysis of the ATAC trial. Lancet Oncol. 2006 Aug;7(8):633-43. doi: 10.1016/S1470-2045(06)70767-7. PMID: 16887480.
- Geisler J, King N, Dowsett M, et al. Influence of anastrozole (Arimidex), a selective, non-steroidal aromatase inhibitor, on in vivo aromatisation and plasma oestrogen levels in postmenopausal women with breast cancer. Br J Cancer. 1996;74(8):1286-1291. doi:10.1038/bjc.1996.531.
- Available from https://www.bmj.com/content/347/bmj.f7458.
- Aydiner A, Tas F. Meta-analysis of trials comparing anastrozole and tamoxifen for adjuvant treatment of postmenopausal women with early breast cancer. 2008. In: Database of Abstracts of Reviews of Effects (DARE): Quality-assessed Reviews [Internet]. York (UK): Centre for Reviews and Dissemination (UK); 1995-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK75189/.
- Visvanathan K, Fabian CJ, Bantug E, Brewster AM, Davidson NE, DeCensi A, Floyd JD, Garber JE, Hofstatter EW, Khan SA, Katapodi MC, Pruthi S, Raab R, Runowicz CD, Somerfield MR. Use of Endocrine Therapy for Breast Cancer Risk Reduction: ASCO Clinical Practice Guideline Update. J Clin Oncol. 2019 Nov 20;37(33):3152-3165. doi: 10.1200/JCO.19.01472. Epub 2019 Sep 3. PMID: 31479306.
- Chen R, Cui J, Wang Q, Li P, Liu X, Hu H, Wei W. Antiproliferative effects of anastrozole on MCF-7 human breast cancer cells in vitro are significantly enhanced by combined treatment with testosterone undecanoate. Mol Med Rep. 2015 Jul;12(1):769-75. doi: 10.3892/mmr.2015.3427. Epub 2015 Mar 4. PMID: 25738971.
- Pavone ME, Bulun SE. Clinical review: The use of aromatase inhibitors for ovulation induction and superovulation. J Clin Endocrinol Metab. 2013;98(5):1838–1844. doi:10.1210/jc.2013-1328.
- Badawy A, Abdel aal I, Abulatta M. Clomiphene citrate or anastrozole for ovulation induction in women with polycystic ovary syndrome? A prospective controlled trial. Fertil Steril. 2009;92(3):860-3.
- Wu HH, Wang NM, Cheng ML, Hsieh JN. A randomized comparison of ovulation induction and hormone profile between the aromatase inhibitor anastrozole and clomiphene citrate in women with infertility. Gynecol Endocrinol. 2007;23(2):76-81.
- Tredway D, Schertz JC, Bock D, Hemsey G, Diamond MP. Anastrozole vs. clomiphene citrate in infertile women with ovulatory dysfunction: a phase II, randomized, dose-finding study. Fertil Steril. 2011;95(5):1720-4.e1-8.
- Abu Hashim H. Aromatase Inhibitors for Endometriosis-Associated Infertility; Do We Have Sufficient Evidence?. Int J Fertil Steril. 2016;10(3):270–277. doi:10.22074/ijfs.2016.5040.
- Badawy SZ, Brown S, Kaufman L, Wojtowycz MA. Aromatase inhibitor (anastrozole) affects growth of endometrioma cells in culture. Eur J Obstet Gynecol Reprod Biol. 2015;188:45–50.
- Amsterdam LL, Gentry W, Jobanputra S, Wolf M, Rubin SD, Bulun SE. Anastrazole and oral contraceptives: a novel treatment for endometriosis. Fertil Steril. 2005;84(2):300-4.
- Soysal S, Soysal ME, Ozer S, Gul N, Gezgin T. The effects of post-surgical administration of goserelin plus anastrozole compared to goserelin alone in patients with severe endometriosis: a prospective randomized trial. Hum Reprod. 2004;19(1):160-7.
- Badawy A, Shokeir T, Allam AF, Abdelhady H. Pregnancy outcome after ovulation induction with aromatase inhibitors or clomiphene citrate in unexplained infertility. Acta Obstet Gynecol Scand. 2009;88(2):187-91. doi: 10.1080/00016340802638199. PMID: 19089782.
- Badawy A, Mosbah A, Shady M. Anastrozole or letrozole for ovulation induction in clomiphene-resistant women with polycystic ovarian syndrome: a prospective randomized trial. Fertil Steril. 2008;89(5):1209-12.
- Raman JD, Schlegel PN. Aromatase inhibitors for male infertility. J Urol. 2002 Feb;167(2 Pt 1):624-9. doi: 10.1097/00005392-200202000-00038. PMID: 11792932.
- Helo S, Ellen J, Mechlin C, et al. A Randomized Prospective Double-Blind Comparison Trial of Clomiphene Citrate and Anastrozole in Raising Testosterone in Hypogonadal Infertile Men. J Sex Med 2015;12:1761-9. 10.1111/jsm.12944.
- Alder NJ, Keihani S, Stoddard GJ, Myers JB, Hotaling JM. Combination therapy with clomiphene citrate and anastrozole is a safe and effective alternative for hypoandrogenic subfertile men. BJU Int. 2018;122(4):688-694.
- Raman JD, Schlegel PN. Aromatase inhibitors for male infertility. J Urol. 2002;167(2 Pt 1):624-9.
- Shoshany O, Abhyankar N, Mufarreh N, Daniel G, Niederberger C. Outcomes of anastrozole in oligozoospermic hypoandrogenic subfertile men. Fertil Steril. 2017;107(3):589-594.
- Gregoriou O, Bakas P, Grigoriadis C, Creatsa M, Hassiakos D, Creatsas G. Changes in hormonal profile and seminal parameters with use of aromatase inhibitors in management of infertile men with low testosterone to estradiol ratios. Fertil Steril. 2012;98(1):48-51.
- Dabaja A.A., Schlegel P.N. Medical treatment of male infertility. Transl Androl Urol. 2014;3:9–16.
- Roth MY, Amory JK, Page ST. Treatment of male infertility secondary to morbid obesity. Nat Clin Pract Endocrinol Metab. 2008;4(7):415–419. doi:10.1038/ncpendmet0844.
- Ramasamy R, Ricci JA, Palermo GD, Gosden LV, Rosenwaks Z, et al. Successful fertility treatment for Klinefelter’s syndrome. J Urol. 2009;182:1108–13.
- van Londen GJ, Perera S, Vujevich K, et al. The impact of an aromatase inhibitor on body composition and gonadal hormone levels in women with breast cancer. Breast Cancer Res Treat. 2011;125(2):441–446. doi:10.1007/s10549-010-1223-2.
- Cohen PG. The hypogonadal-obesity cycle: role of aromatase in modulating the testosterone-estradiol shunt–a major factor in the genesis of morbid obesity. Med Hypotheses. 1999;52(1):49-51.
- Holland AM, Roberts MD, Mumford PW, Mobley CB, Kephart WC, Conover CF, Beggs LA, Balaez A, Otzel DM, Yarrow JF, Borst SE, Beck DT. Testosterone inhibits expression of lipogenic genes in visceral fat by an estrogen-dependent mechanism. J Appl Physiol (1985) 2016;121:792–805.