MKI67 and neoplasm: Interestingly, there was a significant correlation for MKI67 (r = 0.904, P = 0.002) and POR (r = 0.932, P = 0.0008) expression between P0 and P2 tumours across the different tumour models, but a poor correlation for SLFN11 expression (r = 0.526, P = 0.18), with P2 tumours from all nine PDX models having lower SLFN11 expression than their corresponding P0 tumours (Figure 5B).