One in six women with breast cancer ‘do not adhere to tamoxifen’

Researchers were surprised to see high rates of non-adherence to tamoxifen in premenopausal women with early-onset breast cancer.

A doctor checking a mamogram for breast cancer

Some 16% of premenopausal women with early-onset breast cancer fail to adequately adhere to tamoxifen, increasing their risk of recurrence and reduced survival, according to the results of a study presented at the European Society for Medical Oncology 2018 Congress in Munich, Germany, on 19 October 2018[1]

In the first study of its kind, researchers measured the serum levels of tamoxifen in 1,799 premenopausal women recently diagnosed with stage I–III breast cancer in order to establish adherence rates.

They discovered that 16% were not adequately adherent at one year according to serum levels of tamoxifen (defined as >60 nanogram/mL). Some 10.7% were non-adherent, meaning they had undetectable levels of the drug in the serum, and 5.3% were defined as “poorly adherent” at three months.

Half of the women with undetectable or low levels of tamoxifen in their serum failed to declare that they were not taking their drugs as prescribed, the researchers found.

Lead researcher Barbara Pistilli, a medical oncologist at Institut Gustave Roussy, Villejuif, France, said she was surprised at the high rate of non-adherence, which was considerably higher than reported previously.

“Women with breast cancer should be encouraged to discuss their treatment and any side effects they experience with their doctor to obtain help to take their therapy.” 


[1] Pistilli B, Paci A, Michiel S et al. Serum assessment of non-adherence to adjuvant endocrine therapy (ET) among premenopausal patients in the prospective multicenter CANTO cohort. Presented at the European Society for Medical Oncology 2018 congress on 19 October 2018. Abstract available here: (accessed October 2018)

Last updated
Clinical Pharmacist, CP, November 2018, Vol 10, No 11;10(11):DOI:10.1211/PJ.2018.20205627

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