Proliferation assay of ZR-75-1 cells expressing HER2 mutants revealed that G309A (P<0.001), S310Y (P<0.01), and P523S (P<0.001) expressing BC cells were significantly more proliferative than H2-WT and S305C expressing BC cells, suggesting that BC cells harboring these mutations may be more aggressive in nature (Fig. 4A). The gene discussed is ERBB2; the disease is breast cancer.