Adherence to oral anticancer medications in metastatic versus nonmetastatic breast cancer patients: Insights from a low-middle-income country

Optimal treatment outcomes in breast cancer rely heavily on patient adherence to oral anticancer medications (OAMs). This study aimed to assess adherence to OAMs and identify factors associated with nonadherence in metastatic and nonmetastatic breast cancer patients. In this cross-sectional study at the National Cancer Institute, Cairo University, 500 breast cancer patients were categorised into metastatic (45.6 %) and nonmetastatic (54.4 %) groups. Adherence was measured using the Morisky Medication Adherence Scale (MMAS-8) and the Medication Possession Ratio (MPR), with nonadherence defined as an MMAS-8 score < 8 or an MPR < 80 %. Data collection was augmented by patient interviews and examinations of outpatient pharmacy dispensing records. Adherence rates were 46.4 % as per MMAS-8 and 71 % according to MPR. Specifically, in the nonmetastatic group, MMAS-8 revealed a 28.3 % adherence rate, MPR showed 75.4 % adherence rate. Metastatic patients displayed significantly higher adherence (MASS-8, 68 %) ( p < 0.001). There was a notable inverse correlation between adherence and the severity of side effects like musculoskeletal pain, neurological symptoms, fatigue, and hot flushes ( p < 0.001). Additionally, adherence varied with treatment duration, with shorter periods associated with better adherence. This study confirms that adherence to OAMs is significantly affected by both the metastatic status and the severity of side effects. This highlights the urgent need for enhanced educational and management strategies tailored to the specific challenges faced by breast cancer patients, especially those dealing with severe side effects. Ongoing research should focus on developing and testing targeted interventions to improve adherence in these patient groups. • Metastatic breast cancer patients show higher medication adherence than non-metastatic. • Dual-method assessment reveals significant gaps between self-reported and pharmacy data. • Severe side effects and prolonged treatment reduce adherence in breast cancer patients. • Premenopausal women face greater adherence challenges requiring targeted interventions. • Real-world adherence data guides tailored pharmacist-led adherence interventions.