ESR1 and breast cancer: Nevertheless, somatic alterations accounted for the greatest proportion of variance in expression on a per-gene basis across all cancer types (mean proportions of variance for somQTLs = 0.02 (thyroid cancer) – 0.15 (ER + breast cancer); mean proportions of variance in expression accounted for by eQTLs were lower (0.01 (skin cutaneous melanoma) – 0.05 (uveal melanoma)).