ABCG2 and cancer: Moreover, ABCG2- cells exhibited higher sphere formation than ABCG2+ cells,111 which is consistent with the findings in a study published more than 10 years ago.112 Patrawala indicated that ABCG2+ cancer cells can generate ABCG2- cells and ABCG2- cancer cells can also generate ABCG2+ cells.112 Another study showed that ABCG2 activity was not responsible for the stem-like phenotypes of CSCs.113 At present, the more pertinent conclusion is that the SP fraction is composed of heterogeneous cell populations.