Clinical Application of Volumetric Absorptive Microsampling for Therapeutic Drug Monitoring of Oral Targeted Anticancer Drugs.

Background: Therapeutic Drug Monitoring optimizes oral anticancer drug treatment by measuring plasma levels. Volumetric absorptive microsampling (VAMS) allows home sampling with a minimal blood sample. However, methods for converting whole blood into plasma are required to interpret these results. This study aimed to establish conversion methods for abiraterone, alectinib, cabozantinib, imatinib, olaparib, sunitinib, and their metabolites, while assessing the differences between venous and capillary blood. The feasibility of home sampling was also evaluated.

Methods: Plasma and VAMS samples, both from venipuncture-collected whole blood tubes and from a finger prick, were collected from each patient. The VAMS samples were deemed comparable if their concentrations were within ±20% of each other for ≥2/3rd of the patients. The Passing-Bablok regression and conversion factor methods were tested for the plasma and VAMS finger prick samples. The estimated plasma concentrations using both methods were required to be within ±20% of the measured plasma concentrations for ≥2/3rd of the pairs.

Results: Overall, 153 patients were enrolled in this study. Conversion methods were applied to the VAMS samples, and the acceptance criteria were met for alectinib-M4, cabozantinib, imatinib, N-desmethyl imatinib, olaparib, sunitinib, and N-desethyl sunitinib but not for abiraterone, D4A, or alectinib. The capillary and venous VAMS concentrations were similar, except for that of D4A. Patients were positive toward home sampling.

Conclusions: The established VAMS conversion methods for 7 out of 10 oral targeted anticancer drugs or metabolites met the acceptance criteria. Future studies need to validate the conversion methods with an independent cohort and integrate home sampling via VAMS to provide patients with an alternative to venipuncture at the outpatient clinic.