NZ 598489 Disclosed is a pharmaceutical composition comprising: a tubulin polymerisation inhibitor; and a mTOR inhibitor, wherein the tubulin polymerisation inhibitor is a compound of formula (Ib) as defined in the complete specification or a salt, solvate or disodium phosphate prodrug thereof. Also disclosed is the use of said pharmaceutical composition in the manufacture of a medicament for the treatment of a proliferative disease.