Adherence to Adjuvant Hormonal Therapy Among Commercially Insured Women With Breast Cancer

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In a study reported in JCO Oncology Practice, Zhao et al found that 5-year adherence to adjuvant hormonal therapy was low among commercially insured women with breast cancer in the United States.

The retrospective observational study used data from the IBM MarketScan Research Databases to identify 80,224 women with breast cancer who underwent breast cancer surgery between 1999 and 2015. Raw adjuvant hormonal therapy initiation rates were calculated, and standardized rates were obtained by adjusting for Surveillance, Epidemiology, and End Results (SEER) hormone receptor–positive breast cancer incidence rates.

Medication possession ratios were calculated as prescription filled days divided by total days in the prescription period among patients with ≥ 12 months of continuous coverage. Treatment adherence was defined as medication possession ratios of ≥ 80%.

Key Findings

The raw initiation rate was 71.8% (n = 57,571). The standardized initiation rate was 87.5%, increasing from 84.6% in 1999 to 90.0% in 2015.

Overall, 61.2% of patients initiated treatment with aromatase inhibitors and 38.8% with tamoxifen. Nearly all patients initiated adjuvant hormonal therapy with tamoxifen in 1999, with the rate decreasing to approximately 50% in 2003 and approximately 30% in 2015. Overall, 69.9% of patients used one type of adjuvant hormonal therapy, and 30.1% switched between two or more types of adjuvant hormonal therapy.

A total of 49,897 patients with ≥12 months of continuous prescription insurance coverage since first adjuvant hormonal therapy claim were assessed for adherence. Adherence rates were 82.8%, 76.4%, 72.6%, 70.1%, and 65.5% at, 1, 2, 3, 4, and 5 years. Among 13,824 patients with ≥ 5 years of insurance coverage, adherence rates were 84.4%, 78.3%, 73.8%, 71.1%, and 65.2% at 1, 2, 3, 4, and 5 years.

Adherence rates ranged from 65.7% with tamoxifen to 76.4% with anastrozole among single agents. Rates were 66.2% among patients using two regimens and 57.7% among those using more than two regimens. 

Prescription by mail-in order; using a single adjuvant hormonal therapy regimen; age 50 to 69 years; a monthly out-of-pocket drug payment ≤ $11; absence of depression; absence of comorbidity; living in the Northeast; treatment in recent years; and receipt of the combination of chemotherapy, radiation, and surgery were significantly associated (all P < .01) with higher adherence rates.

The investigators concluded, “Five-year adjuvant hormonal therapy adherence rates are low among female patients with breast cancer with private health insurance. Effective approaches to improve adjuvant hormonal therapy adherence are needed.”

Hui Zhao, PhD, of The University of Texas MD Anderson Cancer Center, is the corresponding author for the JCO Oncology Practice article.  

Disclosure: The study was supported in part by a grant from the National Cancer Institute. For full disclosures of the study authors, visit

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