The impact of COVID-19 pandemic on treatment adherence of patients with breast cancer

Purpose: Oncology patients may require long-term treatment adherence and may face additional challenges to adherence during national crises. This study investigated changes in treatment adherence among breast cancer patients before and during the COVID-19 pandemic. Methods: A historical prospective study was conducted using electronic medical records of adult breast cancer patients in the post-acute treatment phase; those receiving preventive oral monotherapy were analyzed. Adherence was assessed using the proportion of days covered (PDC). Results: The pre-pandemic baseline PDC among 4274 patients was 78.5%. During the four COVID-19 waves (Feb 2020–Oct 2021), patients with low pre-pandemic adherence (PDC < 75%) showed a significant increase in adherence (from 59 to 77%), while those with high pre-pandemic adherence (PDC < 75%) experienced a decline (from 94 to 88%). A statistically significant decline was observed from wave 1 (85.69%) to wave 4 (80.69%), p < 0.001. Older age was associated with higher adherence (p.(0.001 > Patients vaccinated during the third wave exhibited a significant decline in adherence between the first and fourth waves (p < 0.001). Conclusions: This study emphasizes the need to monitor and support medication adherence among patients with chronic oncology conditions during health crises. The COVID-19 pandemic revealed shifts in adherence patterns, highlighting the urgency of improving healthcare preparedness, enhancing access to services, and ensuring treatment continuity in future emergencies.