ERBB2 and breast cancer: Breast cancer cell line MCF-7 (barely expresses HER2), BT474 (strongly expresses HER2) and SKBR3 (strongly expresses HER2) were cultured and treated with different concentrations of HER2-nanobody [the following were designated as MCF-7/BT474/SKBR3-HER2-VHH (-treatment concentration)] or Negative control nanobody (HSA-nanobody, NC-VHH).