Endocrine therapy use among elderly hormone receptor-positive breast cancer patients enrolled in Medicare Part D.

Background: Clinical guidelines recommend that women with hormone-receptor positive breast cancer receive endocrine therapy (selective estrogen receptor modulators [SERMs] or aromatase inhibitors [AIs]) for five years following diagnosis.

Objective: To examine utilization and adherence to therapy for SERMs and AIs in Medicare Part D prescription drug plans.

Data: Linked Surveillance, Epidemiology, and End Results (SEER)-Medicare data.

Study design: We identified 15,542 elderly women diagnosed with hormone-receptor positive breast cancer in years 2003-2005 (the latest SEER data at the time of the study) and enrolled in a Part D plan in 2006 or 2007 (the initial years of Part D). This permitted us to compare utilization and adherence to therapy at various points within the recommended five-year timeframe for endocrine therapy. SERM and AI use was measured from claim records. Non-adherence to therapy was defined as a medication possession ratio of less than 80 percent.

Principal findings: Between May 2006 and December 2007, 22 percent of beneficiaries received SERM, 52 percent AI, and 26 percent received neither. The percent receiving any endocrine therapy decreased with time from diagnosis. Among SERM and AI users, 20-30 percent were non-adherent to therapy; out-of-pocket costs were higher for AI than SERM and were strongly associated with non-adherence. For AI users without a low income subsidy, adherence to therapy deteriorated after reaching the Part D coverage gap.

Conclusions: Many elderly breast cancer patients were not receiving therapy for the recommended five years following diagnosis. Choosing a Part D plan that minimizes out-of-pocket costs is critical to ensuring beneficiary access to essential medications.