Objectives Adherence to long-term pharmacological treatment for breast cancer is less than optimal. To date, only a limited number of population-based studies have assessed adherence to adjuvant hormonal treatment (AHT), though it is a treatment with proven benefit in terms of reduction of recurrence and mortality. The aim of this study was to examine the rate of adherence in women that opt for hospital direct drug distribution.

Methods An administrative programme (Diapason) was used to perform a population-based retrospective observational study, listing patients with access to local hospital direct drug distributions (dates and drug dispensed). A total of 326 patients being treated with anastrozole (n=121), letrozole (n=69), exemestane (n=27) or tamoxifen (n=110) were monitored in the period between 1 January 2005 and 31 December 2009. Adherence to AHT was calculated and classified as poor, low, moderate, good or excellent.

Results Over 46% of patients demonstrated poor/moderate adherence, 20% good and only 34% showed an excellent adherence to AHT. The group of women that began treatment with anastrozole was the group that underwent the fewest number of switches to other treatments (2.5%), vs letrozole (5.8%) and exemestane (7.4%). During the 5 years of follow-up only one woman in every two carried out the adjuvant treatment.

Conclusions This study shows a poor level of adherence to AHT over 5 years of follow-up. Early discontinuation and non-adherence to AHT were commonly associated with increased mortality. Further efforts must be undertaken to promote adherence over the entire recommended treatment period.