We then conducted a 3-(4,5)-dimethylthiazol-2-yl-2,5-diphenyltetrazoliumbromide (MTT) assay to evaluate the effect of plant-derived anti-HER2VHH-FcK on the viability of HER2-positive breast cancer cells (Figure 4c,d). Here, ERBB2 is linked to breast carcinoma.