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Cancer. 2019 Feb 1;125(3):374-381. doi: 10.1002/cncr.31910. Epub 2018 Dec 19.

The impact of state parity laws on copayments for and adherence to oral endocrine therapy for breast cancer.

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Department of Radiation Oncology, Stanford Cancer Institute, Stanford, California.
Quantitative Sciences Unit, Stanford University School of Medicine, Stanford, California.



Adherence to endocrine therapy for breast cancer is often inadequate, in part because of out-of-pocket costs for medication. Numerous states have enacted parity laws to limit patient cost-sharing for oral anticancer drugs. The objective of this study was to estimate the impact of these laws on patient copayments for and adherence to oral endocrine therapy for breast cancer.


Administrative health insurance claims data from 2007 to 2014 derived from a US health care database were used to identify female patients aged 18 to 64 years with invasive cancer or ductal carcinoma in situ of the breast who initiated endocrine therapy and were enrolled in fully insured health plans in states that either enacted parity legislation between 2008 and 2013 or had not yet enacted such legislation by 2015. Differences-in-differences analysis was used to compare copayments for and adherence to endocrine therapy during the 1-year period before and after each year of legislation enactment.


In total, 6900 individuals who received 7778 unique drug therapy courses were identified. Parity legislation was associated with significant decreases in the 25th percentile of copayments for anastrozole of $4.39 (95% confidence interval [CI], -$4.52 to -$4.26; P < .001) and for exemestane of $3.08 (95% CI, -$4.80 to -$1.35; P < .001). The median copayment for exemestane decreased by $10.25 (95% CI, -$12.61 to -$7.89; P < .001). A higher median monthly copayment was significantly associated with a greater risk of medication nonadherence (adjusted risk ratio, 1.006 per dollar increase; P < .001).


Parity laws had a modest effect on lowering the cost of anastrozole and exemestane, but more focused efforts to limit out-of-pocket costs for endocrine therapy may have a greater impact on medication adherence.


adherence; breast cancer; endocrine therapy; oral parity; out-of-pocket cost

[Available on 2020-02-01]

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