While SLCO1A2 and SLCO1B3 likely mediate doxorubicin uptake and clearance61 at reported circulating concentrations14,40,41, it is notable that cardiomyocytes and cancer cells exhibit distinct uptake kinetics62 and we find that other transport systems likely mediate doxorubicin uptake into breast cancer cells. Here, SLCO1B3 is linked to breast carcinoma.