Abstract: A pharmaceutical composition is provided having particles of a physical mixture that contain at least one 20-camptothecin or a derivative thereof, at least one surfactant, at least one stabilizer, and at least one diluent. The particles have a mean particle size of less than about 2500 nm. The pharmaceutical composition can be nano- or micro-sized particles containing the 20-camptothecin esters or derivatives thereof as part of a physical mixture, which can provide the active compound in a water-soluble/dispersible, bioavailable form. The particles can be used as an oral pharmaceutical composition which comprises the nano- or micro-sized form of 20-camptothecin esters or derivatives, such as in an oral suspension (e.g., an aqueous suspension), or capsules, or caplets. The pharmaceutical composition can be used in the treatment of a cancer or malignant tumor in a patient by oral administration thereof in a therapeutically effective amount.