Our findings revealed that reduced stemness and proliferative capacity in G2/M-accumulated cells mediated by ABCB1 inhibition decreased the level of drug sensitivity in p53null ovarian cancer cells, but not in p53-expressing cells, suggesting that the strategy to overcome acquired resistance to carboplatin might differ depending on the mutation status of the TP53 gene. The gene discussed is ABCB1; the disease is ovarian carcinoma.