Drug Therapy Problems and Disease Progression in Patients with HER2+ Breast Cancer in a Philippine Tertiary Hospital

Background: Human epidermal growth factor receptor 2-positive (HER2+) breast cancer remains a considerable clinical challenge in the Philippines.Complex antineoplastic regimens, combined with resource-limited public hospital settings, increase the risk of drug therapy problems.This study aimed to evaluate the association between drug therapy challenges and disease progression in patients with HER2+ breast cancer and to identify prescribing patterns and treatment deviations in a tertiary public hospital in the Philippines.Methods: A cross-sectional, retrospective drug utilization review (DUR) was conducted at the Philippine General Hospital (PGH).Medical records of female patients aged 18 years diagnosed with HER2+ breast cancer between January 2022 and December 2023 were reviewed.Patients with complete treatment documentation were included.Antineoplastic regimens were assessed for adherence to National (DOH) and International (NCCN) clinical guidelines.Drug therapy problems were identified and classified into four categories: drug selection, drug form, dose selection, and treatment duration.The primary outcome to be measured was disease progression.Results: Fifty-three eligible patients were included.A total of 519 drug therapy problems were reported, with dose selection accounting for 76.7%, followed by treatment duration (18.3%).Disease progression occurred in 28.3% of patients.Statistical analyses using the Kruskal-Wallis and Fisher's exact tests revealed no significant associations between drug therapy problems and disease progression (p>0.05),although the clinical implications remain concerning. Conclusion:Although no statistically significant association was found between drug therapy problems and disease progression, widespread deviations from guideline-recommended therapy were observed, particularly in dosing and treatment duration.These findings highlight the need for standardized prescribing practices, improved documentation, and systemic interventions in resource-constrained oncology settings.