Abstract P1-08-18: Initiating adjuvant endocrine therapy: Choice of drugs and changes in the patent status of aromatase inhibitors
Authors: Qin X , Huckfeldt P , Virnig BA 
Published: May 2019

Background: Aromatase inhibitors (AIs) and tamoxifen are guideline recommended adjuvant endocrine therapies for postmenopausal women diagnosed with hormone-receptor positive (HR+) breast cancer. Before 2010, all AIs were brand-name, while tamoxifen was generic. In June 2010, anastrozole became the first AI with generic versions available. Generic exemestane became available in April 2011, and generic letrozole in June 2011. We study the associations between the generic drug availability, choice of drug initiated and changes in out-of-pocket (OOP) costs for elderly women in the Medicare program newly diagnosed with HR+ breast cancer.

Methods: From the SEER-Medicare linked database, we selected women whose first HR+ breast cancer was diagnosed at age 65 or older between 2007 and 2013, and who had Medicare Part D (pharmacy) coverage in the 12 months following the diagnosis (or until death).

Results: Prior to the availability of all generic AIs, the average monthly OOP costs of AIs were as high as $150 with a yearly repeating pattern of highs and lows. Consistent with Part D benefit design, the average monthly OOP costs for patients were the lowest around February and the highest around October. The percent of patients who initiated endocrine therapy was stable (60%). After all AIs had generic versions available, the OOP costs decreased, and fluctuations of the average monthly OOP costs disappeared. The OOP costs for the two AIs with the highest market shares stabilized to around $10. The average monthly OOP costs of tamoxifen were constantly around $10. Compared to the dramatic changes in the OOP costs of AIs, the changes in utilization were modest. The percent of patients who initiated any drug increased to 70% in 2012-14. The percent of patients choosing anastrozole, exemestane and tamoxifen increased by 3-5%, while letrozole decreased by 10%, compared to that in 2007-2009. Increases in anastrozole were only substantial before generic letrozole was available (June 2010-May 2011).

Table 1.First Drug Choice among Patients Who Initiated Endocrine Therapy 2007-2009Jan 2010-May 2010Jun 2010-Mar 2011Apr 2011-May 2011Jun 2011-Dec 20112012-2014Generic AvailabilityNo Generic AINo Generic AI1 Generic AI2 Generic AIsAll AIs GenericAll AIs GenericAnastrozole59.3%58.4%69.2%77.1%68.0%64.6%Letrozole28.3%28.9%20.0%8.4%12.8%18.3%Exemestane3.4%2.6%1.6%3.5%6.7%4.7%Tamoxifen9.0%10.1%9.2%11.0%12.5%12.4%

Table 2.Range of the Average Monthly Out-of-Pocket Costs ($)Anastrozole37-13545-7212-9910-1111-139-13Letrozole39-13742-7941-15063-7823-788-18Exemestane30-14149-7349-13540-4646-6133-56Tamoxifen6-148-108-98-88-98-11

Conclusions: With generic entry, dramatic decreases in the prices and increases in initiations would be expected. We saw dramatic decreases in average monthly OOP costs. Changes in choice of AI were modest, especially considering tamoxifen initiation also increased after all generic AIs were available.

Citation Format: Qin X, Huckfeldt P, Virnig BA. Initiating adjuvant endocrine therapy: Choice of drugs and changes in the patent status of aromatase inhibitors [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P1-08-18.