ESMO 2018 – One in six premenopausal breast cancer patients inadequately adherent to tamoxifen after one year

  • Jo Whelan
  • Oncology Conference reports
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  • One in six premenopausal women (16%) showed inadequate adherence to tamoxifen after one year.
  • 10.7% had undetectable serum levels, indicating complete nonadherence.
  • Self-declaration is not a reliable indicator of adherence.
  • Doctors should ask about side effects, encourage openness about nonadherence, and work with patients on strategies to help them adhere.

Why this matters

Nonadherence to long-term hormonal therapy (ie, taking

Key results

  • 16.0% (188/1177) of premenopausal women prescribed tamoxifen in the CANTO trial showed inadequate adherence at one year (based on serum assessment of tamoxifen
  • Within this group, 10.7% of the total population under study had undetectable levels of tamoxifen and were classed as nonadherent.
  • Half of those with inadequate adherence had self-declared as adherent.

Study design

  • CANTO COMPLETE was a pre-defined substudy of CANTO, a French prospective longitudinal study of 12,000 patients with recently diagnosed stage I-III breast cancer. The objective of CANTO is to characterize the long-term impact of treatment toxicities.
  • CANTO COMPLETE examined the prevalence and predictors of nonadherence to hormone therapy in premenopausal women, using serum assessment of drug levels and matching them with patients’ self-declaration of adherence.


Serum tamoxifen was measured at only one time point, reflecting levels over the previous month only.


“Non-compliance with adjuvant hormonal treatment is an under-appreciated and under-reported problem and places patients at risk of inadequate clinical benefit,” said ESMO’s invited commentator, Giuseppe Curigliano, University of Milan, Italy.