Does the Time of Day at Which Endocrine Therapy Is Taken Affect Breast Cancer Patient Outcomes?

Background: Non-compliance and non-persistence with endocrine therapy for breast cancer is common and usually related to treatment-induced side effects. There are anecdotal reports that simply changing the time of day when taking endocrine therapy (i.e., changing morning dosing to evening dosing or vice versa) can reduce side effects. Literature review: We conducted a literature review to evaluate whether changing the timing of tamoxifen and/or aromatase inhibitor administration impacted patient outcomes. No randomized control trials or prospective cohort studies that looked at time of day of endocrine therapy were identified through our review of literature from 1947 until August 2020. Conclusions: Given the rates of endocrine therapy non-compliance and non-persistence reported in the literature, ranging from 41-72% and 31-73%, respectively, simply changing the time of day when medications are taken could be an important strategy. We could identify no trials evaluating the effect of changes in timing of administration of endocrine therapy on breast cancer patient outcomes. Randomized control trials are clearly indicated for this simple and cost-effective intervention.