The Medicare Prescription Drug, Improvement, and Modernization Act of 2003 authorized optional prescription drug coverage (Part D) for eligible beneficiaries beginning January 1, 2006. Unlike Medicare Parts A and B, Medicare coverage of prescription drugs relies on private plans within the various states; these plans are allowed wide discretion when setting features and prices. In order to ensure some degree of consistency across states, the Part D legislation included substantial regulatory oversight requiring plans to offer actuarially equivalent benefits, provide coverage of certain medications, and supply coverage information for a single Centers for Medicare & Medicaid Services (CMS) Web site to facilitate consumer comparison. A number of recent studies, however, suggest that drug utilization under Part D has been uneven, with prescription drug use among Part D enrollees varying significantly by geographic regions.1,2
Adjuvant endocrine therapy for breast cancer is a useful model for studying the relationship between pharmaceutical plan characteristics and choice of therapy. For most postmenopausal women with hormone receptor–positive (HR+) disease there are essentially 2 options for oral endocrine therapy: tamoxifen, whose efficacy was initially demonstrated in the mid-1980s,3 or an aromatase inhibitor (AI). Beginning in 2005, recommendations from ASCO suggested that adjuvant therapy for postmenopausal women with HR+ breast cancer include an AI, either alone or in sequence after tamoxifen.4 For much of the past decade, AI agents have been significantly more expensive than tamoxifen, with average costs exceeding $300 USD monthly.5 Although AI agents recently became available in generic formulations with a considerably lower cost to the patient, historical patterns of use of breast cancer–specific endocrine therapies provide useful insights into the ways patients respond to various plan features. In addition, given the expanding number of expensive oral chemotherapy agents and the fact that several malignancies, such as chronic myeloid leukemia (CML) and renal cell carcinoma, have multiple oral treatment options available, our study provides an analytical framework that is applicable to other situations.
This article examines the extent to which geographic variation in Medicare Part D plan characteristics contribute to the variation in choice of initial endocrine therapy agent among women with early-stage breast cancer enrolled in Part D. To that end, we first quantified the net contribution of state of residence in women's probability of choosing the more expensive AIs, as opposed to tamoxifen, as the initial hormonal therapy agent. In a second-stage estimation, we examined whether state pharmaceutical plans' characteristics, such as annual AI drug costs, deductibles, premiums, and cost-sharing, significantly explain such state effects.
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. Winer EP Hudis C Burnstein HJ American Society of Clinical Oncology technology assessment on the use of aromatase inhibitors as adjuvant therapy for postmenopausal women with hormone receptor-positive breast cancer: status report 2004. J Clin Oncol 2005; 23: 619– 629.
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