The present invention relates to a compound representedby the formula:(see formula I)wherein W is C(R1) or N, each A is an optionally substitutedaryl group or a heteroaryl group, X1 is -NR 3-Y1-, -O-, -S-,-SO-, -SO2- or -CHR3- wherein R3 is a hydrogen atom or anoptionally substituted aliphatic hydrocarbon group, or R3 isoptionally bonded to A to form an optionally substituted ringstructure, R1 is a hydrogen atom or an optionally substitutedgroup bonded via a carbon atom, a nitrogen atom or an oxygenatom, R2 is a hydrogen atom or optionally substituted groupbonded via a carbon atom or a sulfur atom, or R1 and R2, or R2and R3 are optionally bonded to form an optionally substitutedring structure, or a salt thereof, and a tyrosine kinaseinhibitor or an agent for the prophylaxis or treatment ofcancer, which contains this compound or a prodrug thereof.
