Serum Analysis Confirms Poor Tamoxifen Adherence Among Premenopausal Breast Cancer Patients

A discrepancy has been detected between self-reported adherence to tamoxifen treatment and serum levels of the drug in premenopausal breast cancer patients

medwireNews: Sixteen percent of premenopausal women do not adhere to tamoxifen within a year of beginning treatment, suggests serum analysis presented at the ESMO 2018 Congress in Munich, Germany. 

Moreover, self-reported adherence to treatment was not confirmed by the laboratory test in 55.3% of cases, prompting the CANTO-Complete Study authors to recommend that “a multi-method approach” should be used for future investigations. 

“Serum assessment, compared to subjective approaches, may provide more accuracy in defining patient’s adherence, even though it cannot capture treatment interruptions and restarts or missing doses”, said presenting author Barbara Pistilli, from Gustave Roussy in Villejuif, France. 

The research focused on the younger participants of the CANTO study, a longitudinal study of 11,237 patients attending 26 French cancer centres between 2012 and 2018 with hormone receptor-positive stage I–III disease. 

Premenopausal patients are known to be less adherent to adjuvant endocrine therapy than their postmenopausal counterparts, with nonadherence to tamoxifen associated with poorer survival, the presenter explained. 

The 1177 premenopausal patients using tamoxifen were aged a median of 45 years and of these 51.0% had a high school education or above and 64.6% had received neoadjuvant or adjuvant chemotherapy. 

Overall, quality of life assessed using the QLQ-C30 questionnaire indicated that 40% of patients had severe fatigue and 42% severe insomnia. In addition, 75% suffered from hot flushes of any grade, 51% from gynaecological side effects and 50% from musculoskeletal symptoms, while Hospital Anxiety and Depression scores indicated that 41% had anxiety and 8% depression. 

The majority of the patients (84.0%) were adherent to tamoxifen, as defined by a serum concentration of 60 ng/mL or higher at the 1-year follow-up. Among the nonadherent patients, 126 had levels below 15 ng/mL and 62 had a concentration of 15–60 ng/mL. 

However, 87.7% of the patients had self-declared adherence to tamoxifen at this time, with 12.3% admitting treatment interruption (n=57), discontinuation (n=52) or a switch to aromatase inhibitor therapy because of toxicity (n=37). 

Of the 188 patients who had nonadherent serum samples, just 44.6% had self-declared nonadherence; by contrast, 6.2% of 989 patients had an adherent serum sample despite self-reporting treatment interruption (n=50), switch to aromatase inhibitor therapy (n=8) or treatment discontinuation (n=3). 

Overall, there was 86% concordance between the serum findings and self-declarations, with a “moderate association” between the two measures, said Barbara Pistilli. 

Analysis of the patients by a raft of sociodemographic and disease-related characteristics indicated that not receiving chemotherapy and not having musculoskeletal toxicity were both strongly associated with nonadherence to tamoxifen, with significant odds ratios of 1.85 and 0.65, respectively. 

Barbara Pistilli summarised that CANTO-COMPLETE is the first prospective study to evaluate nonadherence to tamoxifen or aromatase inhibitor therapy for over 5 years using both serum assessments and patient declarations, thus providing “therapeutic drug monitoring” to better understand the relationship between adverse events and adjuvant endocrine therapy. 

Furthermore, CANTO-COMPLETE will “inform the design of a targeted behavioral intervention to prevent non-adherence to adjuvant [endocrine therapy]” both in premenopausal patients and those with breast cancer in general, she concluded. 



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. ESMO 2018 Congress, 19-23 October, Munich, Germany (185O_PR).

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