Cancers, particularly solid tumors (e.g., breast, lung, renal, colon and ovarian cancers and melanomas) and cancers of the hematologic system, e.g., hemopoietic cancers such as leukemias, lymphomas or myelomas, are treated by administration of a therapeutically effective amount of a compound having the formula (1): (I)in which the quinoline ring is substituted by from one to three groups selected from halogen and trifluoromethyl (designated in the formula by “A”), and is optionally further substituted by one or more other moieties and R is (a) NR1R2 in which R1 and R2 are independently hydrogen or C1-C4 alkyl; (b) 2-piperidyl, (c) 2-pyridyl, and (d) 5-(ethyl or vinyl)-quinuclidin-4-yl; an enantiomer of such a compound; a pharmaceutically acceptable salts of such a compound or of an enantiomer thereof; a prodrug of such a compound or of an enantiomer thereof; a metabolite of such a compound or of an enantiomer thereof; and mixtures of two or more of the foregoing. A particularly preferred compound is mefloquine.