Recognizing Nonadherence to Tamoxifen in Early Breast Cancer Patients

In premenopausal patients with early breast cancer, approximately one-sixth are not adequately adherent to adjuvant endocrine therapy, according to a new study. Recognizing nonadherence could allow for targeted interventions to improve the situation.

“This issue is important because nonadherence with hormonal therapy-meaning taking less than 80% of prescribed treatment-can be associated with higher risk of mortality and shorter time to recurrence of breast cancer,” said Barbara Pistilli, MD, of the Institut Gustave Roussy in Villejuif, France, according to a press release. She presented results of an analysis from the CANTO cohort at the European Society for Medical Oncology (ESMO) 2018 Congress, held October 19–23 in Munich.

The CANTO cohort is a longitudinal study that will include 12,000 patients with early breast cancer. In the new analysis, researchers included 1,228 premenopausal patients treated with endocrine therapy, with follow-up to at least 1 year. Most patients were prescribed tamoxifen, though smaller numbers received tamoxifen plus luteinizing hormone-releasing hormone (LHRH) analogs, an aromatase inhibitor plus LHRH analogs, or an unknown endocrine therapy regimen.

The patients prescribed tamoxifen were assessed at 1 year based on liquid chromatography-tandem mass spectrometry, and adherence was defined as follows: nonadherent if serum tamoxifen concentration was 15 ng/mL or lower; poorly adherent if concentration was 15–60 ng/mL; and adherent if the concentration was above 60 ng/mL.

Of 1,177 patients prescribed tamoxifen, 188 (16.0%) were not adequately adherent to tamoxifen. More than 1 in 10 (10.7%) were nonadherent, and 5.3% were measured as being poorly adherent. An analysis of patient self-reports showed that at least half of patients with low or undetectable levels of tamoxifen did not declare that they were not taking the medication as prescribed.

“I was surprised at the high rate of nonadherence, which was considerably higher than reported previously,” said Pistilli. “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.”

Giuseppe Curigliano, MD, PhD, of the European Institute of Oncology at the University of Milan in Italy, commented on the study, and said that these results should spur the creation of strategies to combat nonadherence. “Noncompliance with adjuvant hormonal treatment is an underappreciated and underreported problem and places patients at risk of inadequate clinical benefit,” he said. “Taking into account that many high-risk premenopausal women worldwide are receiving aromatase inhibitors plus ovarian suppression, both inducing more side effects than tamoxifen, we are underreporting the nonadherence rate in real life.”