1. ¹Division of Community Health Sciences, University of Dundee, MacKenzie Building, Kirsty Semple Way, Dundee DD2 4BF, UK
2. ²Department of Radiotherapy and Oncology, Ninewells Hospital and Medical School, Dundee DD1 9SY, UK
3. ³Department of Public Health, University of Aberdeen, School of Medicine, Polwarth Building, Aberdeen AB25 2ZD, UK
4. ⁴Department of Surgery and Molecular Oncology, University of Dundee, Ninewells Hospital and Medical School, Dundee DD1 9SY, UK
5. ⁵Department of General Practice, Royal College of Surgeons in Ireland, 120 St Stephens Green, Dublin 2, Ireland

Correspondence: C McCowan, MRC Research Training Fellow, Division of Community Health Sciences, University of Dundee, MacKenzie Building, Kirsty Semple Way, Dundee DD2 4BF, UK. E-mail: c.mccowan@chs.dundee.ac.uk

Received 1 July 2008; Revised 24 September 2008; Accepted 1 October 2008; Published online 4 November 2008.

Abstract

Increasing duration of tamoxifen therapy improves survival in women with breast cancer but the impact of adherence to tamoxifen on mortality is unclear. This study investigated whether women prescribed tamoxifen after surgery for breast cancer adhered to their prescription and whether adherence influenced survival. A retrospective cohort study of all women with incident breast cancer in the Tayside region of Scotland between 1993 and 2002 was linked to encashed prescription records to calculate adherence to tamoxifen. Survival analysis was used to determine the effect of adherence on all-cause mortality. In all 2080 patients formed the study cohort with 1633 (79%) prescribed tamoxifen. The median duration of use was 2.42 years (IQR=1.04–4.89 years). Longer duration was associated with better survival but this varied over time. The hazard ratio for mortality in relation to duration at 2.4 years was 0.85, 95% CI=0.83–0.87. Median adherence to tamoxifen was 93% (interquartile range=84–100%). Adherence <80% was associated with poorer survival, hazard ratio 1.10, 95% CI=1.001–1.21. Persistence with tamoxifen was modest with only 49% continuing therapy for 5 years of those followed up for 5 years or more. Increased duration of tamoxifen reduces the risk of death, although one in two women do not complete the recommended 5-year course of treatment. A significant proportion of women have low adherence to tamoxifen and are at increased risk of death.