ERBB2 and breast cancer: Analysis of the relative expression of STIM1 and STIM2 revealed a STIM1:STIM2 expression ratio of between 2 and 5 in most breast cancer-derived cell lines investigated, except for the HER2 overexpressing cell line SK-BR-3, which exhibits an expression of STIM1 more than 10 times higher than that of STIM2 [49].