Provide is a method of using a topoisomerase I inhibitor in treatment of cancer to reduce bone marrow suppression. The method includes administering to a subject in need thereof an effective amount of a pharmaceutical composition. The composition has at least one hydrophobic topoisomerase I inhibitor or a pharmaceutically acceptable salt thereof, and at least one polyethylene glycol (PEG) conjugated phospholipid, wherein the molar ratio of said PEG conjugated phospholipid to said hydrophobic topoisomerase I inhibitor or said pharmaceutically acceptable salt of said hydrophobic topoisomerase I inhibitor is about 0.45:1 to about 1.05:1.
