ESR1 and breast cancer: For each metabolite, we calculated the mean value in ERα-positive and ERα-negative BC cell lines, then we extrapolated the difference in the metabolite amount between ERα-positive and ERα-negative BC cell lines and finally we generated a p-value (using Student t-test) corresponding to the differences in metabolite abundance between ERα-positive and ERα-negative BC cell lines (Supplementary Table 2).