ESR1 and breast cancer: Next, we performed Reactome (https://reactome.org/PathwayBrowser/#/) pathway enrichment analysis both for the metabolic proteins identified in either MCF-7 or Y537S cells (Figure 1F; Supplementary Table 1) and for the metabolites that are more abundant in ERα-positive than ERα-negative BC cell lines (green dots in Figure 1G; Supplementary Table 2) and found the de novo purine nucleotide biosynthesis as the only common pathway to the 3 datasets (Figure 1H).