10-Hydroxycamptothecin inhibits the growth of BT-20 and MDA-231 cell with IC50 of 34.3 nM and 7.27 nM, respectively, more potently than camptothecin (CPT) with IC50 of >500 nM. 10-Hydroxycamptothecin is also an impurity of Irinotecan, a Topoisomerase I inhibitor used for the treatment of colon cancer and small cell lung cancer.