An object is to provide a novel therapeutic drug for adult T-cell leukemia having an ATL cell specific antitumor effect. The therapeutic drug for adult T-cell leukemia according to the invention is characterized by containing a compound represented by the formula I or a prodrug thereof,wherein R1 is H, OH, an alkoxy group, an acyl group, or a thioacyl group, R2 is an acyl group, a thioacyl group, CONR7R8, or CSNR7R8 (R7 and R8 being each independently H, an alkyl group containing 1 to 3 carbon atoms, or a phenyl group), or R1 and R2 together may form a ring, X1 and X2 may be the same or different and are each -CR3R4 -SiR3R4- or oxygen, and R3 and R4 may be the same or different and are each an alkyl group containing 1 to 6 carbon atoms.
