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 R 1 is H, OH, an alkoxy group, an acyl group, or a thioacyl group, R 2 is an acyl group, a thioacyl group, CONR 7 R 8 , or CSNR 7 R 8 (R 7 and R 8 being each independently H, an alkyl group containing 1 to 3 carbon atoms, or a phenyl group), or R 1 and R 2 together may form a ring, X 1 and X 2 may be the same or different and are each -CR 3 R 4 -SiR 3 R 4 - or oxygen, and R 3 and R 4 may be the same or different and are each an alkyl group containing 1 to 6 carbon atoms.
