The specificityof the interactions of both anti-HER2 VHH-FcK and Trastuzumab wasconfirmed through independent control experiments conducted on thetriple-negative breast cancer cell line MDA-MB-231, which does notexpress HER2 and BT-474 KD (HER2 knockdown BT-474, Figure S1) cells. This evidence concerns the gene ERBB2 and breast carcinoma.