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Low Adherence to Tamoxifen Therapy Increases Risk of Breast Cancer Recurrence and Early Death

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Key Points

  • A British study of 1,263 women with breast cancer found that patients with low adherence to adjuvant tamoxifen have shorter time to recurrence, increased medical costs, and worse quality of life than women taking daily doses of the drug for 5 years.
  • Recent findings from the ATLAS and aTTom clinical trials suggest that women with estrogen receptor–positive breast tumors have greater protection against cancer recurrence and better overall survival when tamoxifen is taken for 10 years instead of 5 years.

Colin McCowan, PhD, of the University of Glasgow, and colleagues analyzed the prescription records of 1,263 women with breast cancer between 1993 and 2000 to determine how often they took their prescription of adjuvant tamoxifen following surgery and for how long. Women who filled less than 80% of their prescriptions were classified as having low adherence to the treatment. The report was published in the British Journal of Cancer.

The researchers found adherence was low in 475 (38%) women, which was associated with reduced time to recurrence of 52% (P < .001). Time to other cause mortality was also reduced by 23% (P = .055), although this was not statistically significant. For the average patient over her lifetime, the study found low adherence was associated with a loss of 1.43 (95% confidence interval [CI] = 1.15–1.71) discounted life years or 1.12 (95% CI = 0.91–1.34) discounted quality-adjusted life years.

Low adherence was also associated with an added cost of £5,970 ($9,380) compared with high adherence, and the expected value of changing a woman from low adherence to high adherence was calculated to be £33,897 ($53,258), assuming that each quality-adjusted life year is worth £25,000 ($39,280). The reasons for low adherence were not explored in this study.

Better Overall Survival After 10 Years of Tamoxifen

Patients with low adherence have shorter time to recurrence, increased medical costs, and worse quality of life than women who stayed on tamoxifen for 5 years following breast cancer surgery, concluded the researchers. “Interventions that encourage patients to continue taking their treatment on a daily basis for the recommended 5-year period may be highly cost effective,” said the study authors.

Tamoxifen is associated with debilitating side effects, including night sweats, hot flashes, blood clots, strokes, and an increased risk for endometrial cancer. Recent findings from the ATLAS and aTTom trials suggest women with estrogen receptor–positive breast tumors have greater protection against cancer recurrence and better overall survival when tamoxifen is taken for 10 years instead of 5 years. 

This study was funded by the Breast Cancer Campaign.

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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