PPP2R2A and breast cancer: When restricting the analysis to the luminal-like BC subgroup, in the discovery cohort, 41.4% (n = 96) of the cases display PPP2R2A (B55α) -/low expression, while in the validation cohort, these tumors correspond to 42.3% (n = 116) of luminal BC (Additional file 1: Table S5 and Additional file 1: Table S6, respectively).