ients in the interruption group were younger than those in the persistence group. The interruption group also had higher proportions of patients undergoing mastectomy, receiving CT and TT; and a lower proportion receiving tamoxifen only, as opposed to other HT utilization patterns . Similar patterns were found while comparing the HT nonadherence against the adherence groups. The non-adherence group had a significantly higher proportion receiving tamoxifen only, as opposed to having other HT utilization patterns . Adherence and Persistence to Hormone Therapy Interruption and non-adherence measures vary by different definitions and follow-up duration. A systematic review reported a wide range of prevalence of adherence and nonpersistence to HT measured at the end of 5 years of treatment. By applying various definitions in the sensitivity analysis, we found that interruption-associated SKI II mortality increased with increasing interruption frequency, and the non-adherenceassociated mortality increased with the higher percentage for MPR cut-off, supporting a dose-response effect of HT on the survival rate. After adjusting different covariates, this study found elderly age, higher CCI score, lower income, receiving OP and CT, and receiving RT were influencing factors to the interruption- and non-adherence-related mortality. Of which, initial treatment strategies and HT utilization patterns may influence on interruption- and non-adherence-related mortality; hence the study cohort was stratified to avoid indication bias. In line with the National Comprehensive Cancer Network guidelines, surgery is recommended as a standard initial treatment for stages I-II BC, and 94% to 97% BC women who received surgery were at stages I-III in Taiwan. Neoadjuvant CT is generally recommended for stage III BC, and adjuvant HT is recommended for hormone receptor positive 
BC. Similarly, the Taiwan Cancer Registry Report from 20052009 also indicated that 89% of patients receiving neo-adjuvant patients are in stage III. Therefore, by defining the cohort as women with newlydiagnosed BC who received OP and HT, most stages I and II BC cases relevant to the study of adjuvant HT would have been included, and those who received both OP and CT could be considered as having tumors with poorer prognosis. Given that adjuvant HT is used in hormone receptor positive BC, the use of additional CT would be a reasonable surrogate indicator of such poor prognosis in this population-based study. Patients who had CT had greater interruption- and nonadherence-related detrimental effect on survival rates than those who did not have CT. This implies that receiving OP alone could be an indicator for better outcome. The notable difference on survival implies that the clinical benefit of HT is more important in patients who received CT. Previous studies on evaluating the HT discontinuation- or nonadherence-related all-cause mortality were conducted on cohorts with mostly PubMed ID:http://www.ncbi.nlm.nih.gov/pubmed/19649022 postmenopausal women and with stratification according to HT utilization patterns. About 47% of our BC study cohort was diagnosed at 50 years old or younger, and they had higher proportion of interruption and non-adherence compared with the older cohort. As the age of 50 years was a surrogate for menopause, we found the impacts of non-adherence and interruptions on mortality HRs were more marked in the premenopausal group. Non-adherence to AIs may have a greater detrimental effect on survival because AIs have a shorter half-life