We established a Lapatinib-resistant model of HER2+ BC in vitro by treating BT474 cells with a Lap high concentration of 1 μM for 16 days, followed by a gradual increase for 91 days from 0.2 μM Lap to 0.3 μM Lap; this generated a variant referred to as BT474LapRV1. This evidence concerns the gene ERBB2 and breast cancer.