ESR1 and breast cancer: In what became one of the paper's most heavily cited results, Possemato et al. [21] conclusively state that, relative to estrogen receptor-positive breast tumors, estrogen receptor-negative tumors have approximately 68% and 70% elevations of PHGDH, respectively, at the mRNA and protein levels, accounting for an estimated 20–25% of prevalent breast cancer cases and as much as 50% of breast cancer deaths within 5 years of diagnosis [32].