Biologically Based Complementary and Alternative Medicine Use in Breast Cancer Patients and Possible Drug-Drug Interactions.

Purpose: Biologically based complementary and alternative medicine (BB-CAM) is gaining importance. Cancer patients in particular are at risk of interactions between the prescribed medications (intravenous or oral anticancer therapy, concomitant medication, medication for pre-existing illnesses) and BB-CAM. This investigation aims to identify potentially clinically relevant interactions between both BB-CAM and conventional medicine and two BB-CAM products in breast cancer patients (n = 47).

Methods: From March 2020 to January 2021, consecutive breast cancer patients (n = 47) completed a questionnaire about their medication and BB-CAM intake at the beginning of a new intravenous or oral tumor therapy (time point 1) and again after 10 to 12 weeks (time point 2) at the LMU Breast Center in Munich. The collective was divided into two subgroups based on the time after initial diagnosis; a cutoff of 6 months was used. The survey was available through an eHealth application called CANKADO as electronic patient-reported outcome only. Lexicomp^® and AiD Klinik^® databases were used for evaluating potentially clinically relevant interactions. As part of routine care, the collected data were evaluated and cross-checked in interdisciplinary cooperation with the University Hospital Pharmacy LMU.

Results: 43 of the 47 included breast cancer patients (91%) used BB-CAM at some point during their treatment period. We found a significant increase from time point 1 (n = 27) to time point 2 (n = 40) (p = 0.004). Moreover, in the subgroup of newly diagnosed patients, the number significant rose from 17 at time point 1 to 28 at time point 2 (p = 0.007). Overall, we found potentially clinically relevant interactions in 30 of 43 patients (70%). Sixty interactions were detected at both times of investigations. Twenty-three different kinds of BB-CAM-to-BB-CAM (time point 1 [n = 12], time point 2 [n = 11]) or conventional medicine-to-BB-CAM interactions (time point 1 [n = 15], time point 2 [n = 22]) were discovered. Importantly, there was not a single interaction between BB-CAM and an anticancer drug.

Conclusion: Breast cancer patients frequently use BB-CAM. Interactions were detected at both time points of investigation (time point 1 [n = 27], time point 2 [n = 33]). Interactions were particularly evident between BB-CAM substances as well as between BB-CAM and the patients' medication for pre-existing illnesses. Although no interaction between BB-CAM and an anticancer therapy was found, the use of BB-CAM should be evaluated at the beginning and regularly during therapy in view of the substantial number of interactions detected and the large number of upcoming targeted therapies.