The staining has been performed in accordance with the manufacturers’ guidelines; details are presented as Supplementary Materials (Table W1). Protein expression evaluation was performed by two pathologists (H.M. and J.G.) blinded to clinical data. ESR1 and PGR evaluation of the nuclear staining was performed on the basis of Allred score [11]. ERBB2 receptor status was determined on the basis

of the criteria of HercepTest (DAKO) according to the manufacturer’s guidelines, as previously described [12] and [13]. The interpretation BGB324 purchase criteria for the remaining proteins were based on the intensity of the staining and the percentage of cells showing positive reaction (0-100%), which gave the final staining score, as the result of either sum or multiplication, dependent on reported criteria for a particular protein [14], [15], [16], [17], [18], [19] and [20]. Data published on The Human Protein Atlas were also taken into account (http://www.proteinatlas.org/, last accessed: 16 June 2014). Cutoff point determination of expression Protease Inhibitor Library supplier positivity, based on result distribution,

was performed with the use of Cutoff Finder Web Application [21]. Cutoff point determination of the tumor heterogeneity, understood as different staining intensities between the cores belonging to the same STK38 patient, was performed individually for each protein as the proteins differed in staining characteristics. Details are presented as Supplementary Materials (Table W2). For tumor heterogeneity evaluation, staining determination of at least three cores was required. As an example, ESR1 and TOP2A tumor heterogeneity is

presented in the four cores taken from the same primary tumor sample (Figure W1 and Figure W2). Additionally, cumulative heterogeneity was determined for each patient, based on nine proteins that correlated with clinicopathologic characteristics and/or survival (ESR1, PGR, PIK3CA, pAKT1, MYC, TOP2A, CDKN2A, RAD21, and RUNX1). For each patient, a score between 0 and 9 was obtained (1 point for each protein classified as heterogeneous, according to the criteria described in Table W2). On the basis of the result distribution, primary tumors with a score of at least 3 were classified as “globally” heterogeneous. STATISTICA software (version 10; StatSoft Co, Tulsa, OK) was used for all calculations.