Drug-drug interactions in adjuvant and neoadjuvant breast cancer therapy

To determine the prevalence, severity and characteristics of potential drug-drug interactions (DDIs) in a homogeneous cohort of patients with early-stage breast cancer receiving adjuvant or neoadjuvant chemotherapy.

We performed a retrospective observational study of patients treated with systemic chemotherapy at a tertiary hospital. All medications prescribed during chemotherapy were recorded. Potential DDIs were identified using the Lexicomp database and classified by risk level, clinical severity, quality of evidence and mechanism of action. Associations between patient-related factors and DDIs were analysed.

A total of 273 patients were included (median age 52 years) and 56% had at least one comorbidity. Overall, 2842 drugs were prescribed (median 10 per patient), resulting in 2287 potential DDIs. All patients presented at least one DDI; 89% had at least one type D interaction and 14.6% at least one type X interaction. Most DDIs were classified as type C (75.3%), followed by type D (21.7%) and type X (3.0%). The total number of DDIs was significantly associated with age, comorbidity burden and number of prescribed drugs.

Potential DDIs are highly prevalent in patients with early-stage breast cancer receiving chemotherapy, with a substantial proportion involving clinically significant or contraindicated combinations. Polypharmacy, age and comorbidities are key risk factors, highlighting the importance of systematic medication review and interdisciplinary collaboration to improve treatment safety.