The invention provides a compound for use in a method for treating a solid tumor in a patient, wherein the compound is (+)-1,4- dihydro-7-[(3S,4S)-3-methoxy-4-(methylamino)-1-pyrrolidinyl]-4-oxo-1-(2-thiazolyl)-1,8-naphthyridine-3-carboxylic acid and the method comprises administering the compound to the patient in a dose of 10 mg/m2 to 100 mg/m2.