Nonadherence to Tamoxifen Higher Than Reported Among Premenopausal Patients With Breast Cancer

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Half of patients with undetectable tamoxifen levels do not report nonadherence on patient surveys.
Half of patients with undetectable tamoxifen levels do not report nonadherence on patient surveys.

Approximately, 1 in 6 premenopausal women undergoing treatment for early stage breast cancer do not adequately adhere to their prescribed tamoxifen therapy after 1 year of treatment, according to the results of a study presented at the European Society for Medical Oncology (ESMO) 2018 Congress. The study is the first to provide an objective measurement of tamoxifen adherence by measuring serum levels of tamoxifen as opposed to patient surveys.

The issue of nonadherence to hormonal therapy is important because, “taking less than 80% of the prescribed treatment can be associated with higher risk of mortality and shorter time to recurrence of breast cancer,” commented Barbara Pistilli, a medical oncologist at Institut Gustave Roussy, Villejuif, France, and lead author of the study.

For this study, the researchers focused on a subgroup of the larger CANTO cohort, a French prospective study of approximately 12,000 patients, aimed at investigating the long-term impact of side effect associated with breast cancer treatment. A total of 1799 patients with recently diagnosed early stage (I-III) breast cancer, who were prescribed adjuvant hormonal therapy were included.

A startling 16% of patients who were prescribed tamoxifen were not adequately following the treatment 1 year later based on serum levels of tamoxifen. Slightly more than 1 in 10 patients were nonadherent with undetectable levels of tamoxifen. Interestingly, 50% of patients with undetectable levels of tamoxifen did not report their lack of adherence to the treatment on patient surveys.

These results are limited in that the authors only evaluated 1 population. Furthermore, serum levels were measured at only 1 time point. The study is ongoing and aims to assess serum levels of tamoxifen after 3 and 5 years of treatment. 


Pistilli B, Paci A, Michiels S, et al. Serum assessment of non-adherence to adjuvant endocrine therapy (ET) among premenopausal patients in the prospective multicenter CANTO cohort. Oral presentation at: ESMO 2018 Congress; October 19-23, 2018; Munich, Germany. 

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