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Poorer Adherence to Endocrine Treatment Associated With Poorer Outcome in Postmenopausal Hormone Receptor–Positive Breast Cancer

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Key Points

  • Early cessation of treatment was associated with poorer disease-free survival in postmenopausal women with hormone receptor–positive breast cancer receiving adjuvant tamoxifen, letrozole, or sequential letrozole/tamoxifen or tamoxifen/letrozole for 5 years.
  • A compliance score < 90% was associated with poorer disease-free survival.

In an analysis of the Breast International Group (BIG) 1-98 trial reported in the Journal of Clinical Oncology, Chirgwin et al found that poorer adherence to endocrine therapy was associated with poorer disease-free survival in postmenopausal women with hormone receptor–positive breast cancer receiving adjuvant tamoxifen, letrozole, or sequential letrozole/tamoxifen or tamoxifen/letrozole for 5 years.

Study Details

The study analyzed the effects of early cessation of treatment (< 36 months vs ≥ 36 months) and treatment compliance score < 90% on disease-free survival among 6,144 patients receiving at least one dose of study drug. Compliance was defined as taking at least 80% of pills in a drug pack with no breaks longer than 1 week.

Effects of Lower Adherence

On multivariate analysis, early cessation of letrozole (hazard ratio [HR] = 1.45, P = .01), tamoxifen/letrozole (HR = 1.56, 95% confidence interval [CI] = 1.21–2.01), and letrozole/tamoxifen (HR = 1.57, 95% CI = 1.21–2.03) were associated with poorer disease-free survival. Lower compliance score (HR = 1.61, P = .02) was also associated with poorer disease-free survival.

Rates of nonpersistence with study medication were 20.8% with tamoxifen/letrozole, 20.3% with letrozole/tamoxifen, 17.6% with letrozole, and 16.9% with tamoxifen. Adverse events accounted for 82.7% of early discontinuations of treatment. In addition to sequential treatment, factors associated with reduced adherence were older age, smoking, node negativity, and prior thromboembolic event.

The investigators concluded: “Both persistence and compliance are associated with [disease-free survival]. Toxicity management and, for sequential treatments, patient and physician awareness, may improve adherence.”

The Breast International Group 1-98 trial was funded by Novartis.

Jacquie H. Chirgwin, MD, of the Maroondah Breast Clinic, Victoria, Australia, is the corresponding author of the Journal of Clinical Oncology article.

The content in this post has not been reviewed by the American Society of Clinical Oncology, Inc. (ASCO®) and does not necessarily reflect the ideas and opinions of ASCO®.


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