CST3 and breast cancer: The variants W106F‐ and (R24A,R25A)‐cystatin C were included in the experiment, as these variants have been used in another study where it was noted that W106F‐cystatin C resulted in an elevated uptake in MCF‐7 breast cancer cells compared to wild‐type cystatin C and much slower uptake was seen for (R24A,R25A)‐cystatin C [11].