Jeanine Marie Nardin, Evelyn Castillo Lima Vendramini, Thais Abreu de Almeida, Solane Picolotto, Anabel de Oliveira, José Claudio Casali da Rocha

Breast cancer is the most frequent cancer among women. Endocrine adjuvant treatment for estrogen receptor positive breast cancer reduces the recurrence and mortality rates and tamoxifen is the major option, however worse outcomes are associated to improper treatment adherence. Our objective was to evaluate the adherence to tamoxifen in a population of women with breast cancer in South Brazil. We performed a prospective study with newly diagnosed patients and adherence was measured by a self-report questionnaire 4-item Morisky Medication Adherence Scale (MMAS-4), applied to the patients in three, six and twelve months of treatment ,and also through prescription refill rates, assuming the Medication Possession Ratio (MPR). The cohort was composed for 143 patients and by MMAS-4 most patients had high adherence (62% at three months, 68% at six months and 71% at twelve months), however more than 1/4 of the patients showed improper adherence in the 3 time-points evaluated (medium adherence of 37%, 32% and 26% and low adherence of 0.9%, 0% and 2% for three, six and twelve months respectively). It was also verified if there was agreement between MMAS-4 results in the 3 evaluated time-points. Consistency between 3 and 6 months (p=0.046) was observed, but not for 12 months (p=0.705). Also, it was verified a reduction in adherence between 6 and 12 months. Results of prescription refill showed MPR of 98%. No correlation between MMAS-4 and MPR in three months (p=0.310) or twelve months (p=0.105) was observed. The easiness to perform the MMAS-4 questionnaire, the adequacy to low literacy patients and better correlation with literature makes it suitable to be applied in institutional routine. For short time adherence analysis MMAS-4 seems to be more suitable than MPR, even with adherence being over-reported. It is necessary to elaborate interventions that can improve adherence in our population aiming better outcomes.