of the manuscript. Therefore, these patients could be in a more serious condition at diagnosis, and might not response to their primary cancer treatments. All included patients were followed from the disease index date to death or the end of study for the following measures. Interruption and Non-adherence From individual patient’s HT prescriptions issued during the study period, MPR to HT was derived from dividing patient’s `total days of supply’ by `prescription duration’. A conventional cut-off point of PubMed ID:http://www.ncbi.nlm.nih.gov/pubmed/19650784 MPR less than 80% was used to define `non-adherence’. Any gap period between two consecutive HT prescriptions for more than 180 days was defined as `interruption’ . Patients’ adjuvant HT utilization patterns for the two HT types were also categorized into five groups, including tamoxifen only, tamoxifen switched to AIs, AIs only, AIs switched to tamoxifen, and multiple switches between tamoxifen and AIs. Switching of HT was defined as when patient received an alternative type for more than three refills. Mortality Outcome The mortality and date of death were identified from the Registry for Catastrophic Illness. Follow-up time was calculated from the disease index date to the date of death or to the end of study for censored patients. Analysis Variables Adjusted covariates included age of diagnosis, income groups, Charlson Comorbidity Index score, 10083-24-6 biological activity initial treatment strategies, HT initiated year, HT prescription duration. Patients’ age was categorized in four ranks. The three most recently updated NHI insured income ranks were used as a synonym for individual’s monthly income status. Individual’s concomitant conditions recorded within 12 months prior to index date were identified by screening the ICD-9 codes related to CCI, and then converted into a CCI score, and further categorized into three groups. Individual’s BC treatment strategies, including primary surgery, adjuvant chemotherapy, radiation therapy, HT and targeted therapy were identified by corresponding medical-order and drug codes; and those recorded within 12 months posterior to index date were defined as the initial treatment strategies. Patients were stratified by whether they received adjuvant CT into two groups, i.e. OP with or without Adherence and Persistence to Hormone Therapy 6 Adherence and Persistence to Hormone Therapy CT. Trastuzumab was the only TT reimbursed by NHI from April 2002 for HER2 positive BC in accordance with a set of stringent criteria, and thus TT was not included as an adjusting covariate due to limited prescription data. Survival Associated with Interruption and Non-adherence For patients receiving OP with adjuvant CT, the HT persistence group had significantly higher 5-year survival rates when compared against the interruption group . Similar results were also found in patients who did not receive CT. However, the differences of survival rates between interruption and persistence groups were smaller in patients without receiving CT than those receiving CT. Similar patterns were also noted in comparing HT adherence and non-adherence groups. Statistical Analysis The survival rate and all-cause mortality rate were compared between persistence and interruption, and between adherence and non-adherence groups. Overall survival rate was evaluated using Kaplan-Meier survival analysis and stratified by whether patients received initial adjuvant CT. The association between adjusted covariates and all-cause mortality were evaluated 
by both univariate and
