ESR1 and breast cancer: Based on these concepts, the synergistic treatment effect of ruxolitinib and calcitriol combination in luminal B subtype MCF7-HER18 breast cancer cells in our previous study could be interpreted as follows: the antagonistic effect of ruxolitinib and calcitriol combination treatment related to ERα expression can be compensated by the downregulation of HER2 phosphorylation through JAK2 suppression of ruxolitinib.