Breast cancer, placing drug interactions in the spotlight: is polypharmacy the cause of everything?

Purpose Breast cancer is the most prevalent and lethal cancer among women. Forty-one percent of cases occur in people >= 70 years, hindering their treatment given its comorbidities and polypharmacy (PP). Potential drug-drug interactions (PDDI) were analyzed in elderly breast cancer patients between daily and oncospecific treatments and their associations with Age, BMI, Mini Nutritional Assessment (MNA), Frailty categorization, PP, and adverse effects. Patients/methods A cohort of 77 patients >= 70 years with breast cancer who underwent a Comprehensive Geriatric Assessment (CGA) were included. Clinical characteristics were collected using medical records. PDDI between treatments were analyzed using two databases. Data were assessed using linear regression, Chi-square, Mann-Whitney U, and Kruskal-Wallis tests. Finally, a multivariate logistic regression model was built and tested to predict adverse effects. Results From 719 PDDI, 530 (74%) were moderate (r(2) = 0.72) and the median number of drugs during oncospecific treatment (r(2) = 0.73) was 9 (range 3-26). Overall, 59 patients (77%) had adverse effects associated with Frailty categorization and MNA (p < 0.05). The distribution of major, moderate, minor, and total PDDI was associated with PP at CGA and during oncospecific treatment (p < 0.05). Moreover, it was verified that Frailty categorization protects from adverse effects given the intervention made at CGA. Conclusions CGA should be applied in oncologic elderly patients to assess clinical outcomes and categorize them according to their frailty but also to analyze PDDI. Furthermore, we encourage the use of the model in clinical practice for predicting the occurrence of adverse effects, improving therapeutic conciliation.