While we observed that endothelial cells in both sites express BCRP and P-gp, we did not find significant differences in the expression of those two ABC transporters in the endothelial cells of the BCBM versus primary breast cancer tissue in neither the PyMT nor the KB1P BCBM model (Fig. 1, A to D). The gene discussed is ABCG2; the disease is breast carcinoma.