Establishment of human breast cancer cell line SK-BR-3 with Herceptin resistance. (a) Microscopy images showing increased cell proliferation of the SK-BR-3 derivative cell line SK-BR-3 HR in the presence of Herceptin. (b) Differential proliferation rate of SK-BR-3 HR in the presence of Herceptin. Data are means ± standard deviations of three independent experiments. (c) Genotyping of SK-BR-3 and SK-BR-3 HR, showing the two cell lines have the same genetic identity.