This achievement was realizedthrough fusion of the human immunoglobulin G (IgG) Fc domain and KDELendoplasmic reticulum (ER) retention sequence to the VHH fragment.1 This antibody demonstrated its effectivenessin inhibiting the in vitro growth and migration ofBT-474 cell line, which is characterized by HER2 positivity.1 However, it is important to highlight that ourprevious study did not include assays to evaluate the anti-HER2 activityof the VHH-FcK antibody against HER2-positive breast cancer cellsthat are resistant to Trastuzumab. The gene discussed is ERBB2; the disease is breast cancer.