ABCG1 and lung cancer: We found that the Sca-1+Abcg1+cells from Gprc5a-KO mice and SPA+ABCG1+ cells of tumor samples from patients with lung cancer both could develop tumors in the lungs (Fig. 5m), while the Sca-1+Abcg1− and SPA+ABCG1− subsets (Fig. 5l, not P5 subset) failed to initiate tumor formation (Fig. 5m).