ABCB1 and neoplasm: Indeed, our clonal mixture drug assays demonstrated that even if tumor populations contain as little as 25% ABCB1 fusion-negative drug-sensitive cells (75% fusion-positive), chemotherapeutic IC50 values (doxorubicin, paclitaxel and cisplatin) were virtually the same as 100% fusion-negative alone, underscoring the importance of maintaining drug-sensitive populations to outcompete and compete with resistant communities during off-treatment periods.