Relative quantity and variation associated with each candidate EC. a) Quantity of candidate endogenous control genes GAPDH, TFRC, ABL, PPIA, HPRT1, RPLP0, B2M, GUSB, MRPL19, PUM1 and PSMC4 in benign and malignant breast tumour tissue relative to calibrator (QRel. = E-ΔCt). Boxplot shows median value, interquartile-range box and outliers (*). Within gene there was no difference in gene quantities between benign and malignant tissues (P > 0.05). b) Variation associated with candidate endogenous control genes GAPDH, TFRC, ABL, PPIA, HPRT1, RPLP0, B2M, GUSB, MRPL19, PUM1 and PSMC4 in all breast tumours relative to calibrator. Relative gene expression was calculated using the ΔCt method and corrected for efficiency of amplification (QRel. = E-ΔCt). There was a significant difference in variance associated with relative gene expression (P = 0.001) with genes such as RPLP0, TRFC, HPRT1 and GAPDH showing greater variance than genes such as MRPL19 and PPIA.