Consistent with the findings observed in tumour tissues, analysis of published microarray gene expression data from a panel of breast cancer cell lines revealed a striking enrichment of lower CPT1A expression in ER-negative, compared to ER-positive cell lines (Fig. 6g Wilcoxon rank sum test p = 5.41e-10; Fig. 6h Wilcoxon rank sum test p = 3.49e-09). This evidence concerns the gene ESR1 and breast cancer.