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One in six premenopausal early breast cancer patients do not adhere to hormonal therapy

19 Oct 2018
Breast Cancer

MUNICH, Germany - Nearly one in six premenopausal women being treated for early stage breast cancer do not adhere adequately to tamoxifen therapy after one year of treatment, potentially putting themselves at increased risk of recurrence and reduced survival, a French prospective study reports at ESMO 2018 Congress (1).

Hormonal therapy such as tamoxifen is recommended for five to ten years in all patients with hormone receptor-positive breast cancer (2) but previous research has shown that many discontinue long-term therapy (3).


“This issue is important because non-adherence 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 lead author Barbara Pistilli, a medical oncologist at Institut Gustave Roussy, Villejuif, France.

The French study is the first to assess adherence by measuring serum levels of tamoxifen rather than simply asking patients about how they take their treatment; there has previously been limited information on adherence to hormonal therapy in younger women.

“I was surprised at the high rate of non-adherence, 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.”

The study included patients recently diagnosed with early (stage I-III) breast cancer in the CANTO cohort, which is a French prospective study investigating the long-term impact of side-effects with breast cancer treatments in around 12,000 participants. The researchers focused on the sub-group of 1799 (16%) premenopausal women prescribed adjuvant hormonal therapy, assessing their adherence to tamoxifen by measuring serum levels at one, three and five years and comparing this with patients’ self-reports of adherence.

The study is also exploring clinical and social characteristics that could impact on adherence to endocrine therapy with the aim of identifying patients most at risk of not taking endocrine therapy as recommended.

Results showed that nearly one in five (16.0%; 188/1177) of the premenopausal women prescribed tamoxifen were not adequately adherent at one year based on serum assessment of tamoxifen (defined as <60ng/ml)

Just over one in ten (10.7%) were non-adherent, with undetectable levels of tamoxifen. A further 5.3% of patients were poorly adherent, with serum levels of tamoxifen below the steady-state concentration expected after 3 months of treatment.

Analysis of patients’ self-reports showed that at least 50% of patients with undetectable/low tamoxifen levels did not declare they were not taking their tamoxifen as prescribed.

Pistilli commented, “We should take time to explore with patients if they are experiencing side-effects that can affect their adherence, and support them to be open about non-adherence so that we can discuss options to help.” She added, “We need to understand the patients most at risk of being non-adherent early in their treatment and provide targeted interventions aiming to improve their self-efficacy and self-management of side-effects.”

Based on their findings, the researchers now plan to develop an intervention to support improved adherence to hormonal therapy in premenopausal women.

Commenting on the study for ESMO, Giuseppe Curigliano, Head of the Early Drug Development Division at the European Institute of Oncology, University of Milan, Italy, said: “The fact that 16% of patients appeared not adequately adherent to tamoxifen should, in my opinion, suggest strategies to increase adherence.” He warned: “Non-compliance with adjuvant hormonal treatment is an under-appreciated and under-reported problem and places patients at risk of inadequate clinical benefit. 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 under-reporting the non-adherence rate in real life.”

Curigliano suggested, “We need also to identify factors that are associated with poor adherence.” He noted that patients’ beliefs about cancer and their treatment have been shown to be predictive factors for adherence, with fear of recurrence supporting adherence to therapy.

“It is important for physicians to have a good relationship with their patients and get a feel for the patient’s personality to be able to orient discussions positively and potentially counteract any misunderstandings in order to reduce poor compliance with treatment,” he said.

Pistilli acknowledged that limitations of the study included the fact that it was based on a French cohort, so may not necessarily apply elsewhere. It was not designed to investigate patients’ fertility concerns and these are going to be investigated in the future. In addition, serum tamoxifen was measured at only one timepoint, reflecting levels over the previous month, and not across the whole year.

The study will continue to measure serum tamoxifen after three and five years of treatment and the impact of non-adherence on mortality and breast cancer recurrence in long-term follow-up.

Notes to Editors

Please make sure to use the official name of the meeting in your reports: ESMO 2018 Congress

Official Congress hashtag: #ESMO18


  1. Abstract 185O_PR ‘Serum assessment of non-adherence to adjuvant endocrine therapy (ET) among premenopausal patients in the prospective multicenter CANTO cohort” will be presented by Barbara Pistilli during the Proffered Paper Session on Friday, 19 October, 16:00 to 17:30 (CEST) in Room 13 - ICM. Annals of Oncology, Volume 29 Supplement 8 October 2018. The data in the press release are the final data reported at ESMO 2018 and are updated from the initial abstract.
  2. Senkus E, Kyriakides S, Ohno S et al. Primary breast cancer: ESMO Clinical Practice Guidelines for diagnosis, treatment and follow-up. Annals of Oncology 2015; 26 (supplement 5): v8-v30
  3. Hershman DL, Shao T, Kushi LH et al. Early discontinuation and non-adherence to adjuvant hormonal therapy are associated with increased mortality in women with breast cancer. Breast Cancer Res Treat 2011; 126: 529-537
About the European Society for Medical Oncology (ESMO)

ESMO is the leading professional organisation for medical oncology. With 18,000 members representing oncology professionals from over 150 countries worldwide, ESMO is the society of reference for oncology education and information. ESMO is committed to offer the best care to people with cancer, through fostering integrated cancer care, supporting oncologists in their professional development, and advocating for sustainable cancer care worldwide. 

185O_PR  - Serum assessment of non-adherence to adjuvant endocrine therapy (ET) among premenopausal patients in the prospective multicenter CANTO cohort

B. Pistilli1, A. Paci2, S. Michiels3, A. Ferreira4, V. Poinsignon2, P.H. Cottu5, F. Lerebours6, C. Coutant7, A. Lesur8, O. Tredan9, P. Soulie10, L. Vanlemmens11, C. Jouannaud12, C. Levy13, S. Everhard14, P. Arveux7, A.H. Partridge15, S. Delaloge16, F. André17, I. Vaz-Luis16
1Breast Cancer Group, Gustave Roussy, Villejuif, France, 2Pharmacologist Unit and SIPAM, Gustave Roussy, Villejuif, France, 3Team Oncostat, CESP, Gustave Roussy, Villejuif, France, 4Medical Oncology, University of Lisbon, Lisbon, Portugal, 5Medical Oncology, Institut Curie, Paris, France, 6Medical Oncology, Institut Curie Saint Cloud, Saint Cloud, France, 7Medical Oncology, Centre Georges-François Leclerc, Dijon, France, 8Medical Oncology, Institut de Cancérologie de Lorraine, Nancy, France, 9Medical Oncology, Centre Léon Bérard, Lyon, France, 10Medical Oncology, Centre Paul Papin, Angers, France, 11Medical Oncology, Centre Oscar Lambret, Lille, France, 12Medical Oncology, Institut Jean Godinot, Reims, France, 13Medical Oncology, Centre Francois Baclesse, Caen, France, 14UCBG, UNICANCER, Paris, France, 15Medical Oncology, Dana-Farber Cancer Institute, Boston, MA, USA, 16Medical Oncology, Institut Gustave Roussy, Villejuif, France, 17Breast Cancer Unit, Department of Medical Oncology, Gustave Roussy - Cancer Campus, Villejuif, France

Background: Previous studies demonstrated that younger patients (pts) with breast cancer (BC) are more likely to be non-adherent to adjuvant ET, leading to impaired prognosis.

Methods: The CANTO cohort (NCT01993498) is a French multicenter prospective longitudinal study that will include 12000 pts with recently diagnosed stage I-III BC, to characterize long-term impact of BC treatment toxicities. CANTO COMPLETE, a pre-defined sub study, aims to determine, in premenopausal pts who have been prescribed adjuvant ET, the prevalence and dynamic predictors of non-adherence, at 1 (M12), 3 (M36) and 5 (M60) years, using serum assessment of tamoxifen (TAM) and aromatase-inhibitors (AI) matched with pts’ self-declaration. TAM dosage has been determined by liquid chromatography-tandem mass spectrometry on 200 µL of serum. According to standard definitions, adherence to TAM has been defined as: non-adherent if TAM ≤15 ng/mL (≤40 nM), poorly-adherent if TAM 15-60 ng/mL (40-150 nM) and adherent if > 60 ng/mL (>150 nM).

Results: By December 2017, 11237 pts have been included in CANTO, of whom 1799 (16%) are premenopausal and have been prescribed and agreed to take ET: TAM 1496 (83.2%); TAM + LHRH-analogs (LHRH) 26 (1.4%); AI+LHRH 134 (7.5%); unknown 143 (7.9%).We present here the results of TAM plasma assessment at 1 year on all 1228 pts who reached 1 year of follow-up. Overall, 224 (18.2%) pts appeared not adequately adherent to TAM: 162 (13.2%) non-adherent and 62 (5.0%) poorly-adherent. Matching with pts’ self-declaration and clinical determinants of non-adherence will be presented.

Conclusions: At one year from initiation of TAM, plasma measurements show that a substantial proportion of premenopausal pts are not adequately adherent to this treatment. Poorly-adherent pts could benefit from metabolic and pharmacogenetic investigations. Identification of pts at risk of non-adherence allows early targeted interventions to promote adherence in this unique population.

Clinical trial identification: NCT01993498
Legal entity responsible for the study: UNICANCER
Disclosure: All authors have declared no conflicts of interest.

Last update: 19 Oct 2018

This press release contains information provided by the authors of the highlighted abstracts and reflects the content of those abstracts. It does not necessarily reflect the views or opinions of ESMO who cannot be held responsible for the accuracy of the data. Commentators quoted in the press release are required to comply with the ESMO Declaration of Interests policy and the ESMO Code of Conduct.

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