A compound of formula (Ic) or a pharmaceutically acceptable salt thereof where R 1 is C 1-3 alkyl; R 2 is -NR 2a R 2a' or -OR 2b; wherein one of R 2a or R 2'a is H, and R 2b or the other of R 2a or R 2'a is selected from C 1-6 alkyl, haloC 1-6 alkyl, R 2c R 2'c N-C 1-6 alkyl, carbocyclyl, carbocyclylC 1-4 alkyl, heterocyclyl and heterocyclylC 1-4 qalkyl, wherein any of the carbocyclyl or heterocyclyl groups are optionally substituted by one or more groups selected from halogen, C 1-6 alkyl, haloC 1-6 alkyl, C 1-6 alkoxy, haloC 1-6 alkoxy, carbonyl, -CO-carbocyclyl, azido, nitro and cyano, wherein the -CO-carbocyclyl group may be further optionally substituted by one or more groups selected from halogen, C 1-6 alkyl, haloC 1-6 alkyl, C 1-6 alkoxy, haloC 1-6 alkoxy, azido, nitro and cyano; or two adjacent groups on any of the carbocyclyl or heterocyclyl groups together with the interconnecting atoms form a 5- or 6-membered ring which ring may contain 1 or 2 heteroatoms independently selected from O, S and N; or R 2a and R 2'a together with the N-atom to which they are attached form a 5-, 6- or 7-membered ring which may optionally contain 1 or 2 heteroatoms independently selected from O, S and N; wherein the 5-, 6- or 7-membered ring may be further optionally substituted by C 1-6 alkyl; R 2c and R 2'c are independently H and C 1-6 alkyl; each R 3 is independently selected from H, hydroxy, halo, C 1-6 alkyl, halo C 1-6 alkyl, C 1-6 alkoxy, halo C 1-6 alkoxy, nitro, cyano, CF 3, -OCF 3 and -COOR 5; R 4 is hydroxy, halo, C 1-6 alkyl, halo C 1-6 alkyl, C 1-6 alkoxy, halo C 1-6 alkoxy, nitro, cyano, CF 3, -OCF 3; -COOR 5 or-OS 2 C 1-4 alkyl; R 5 is C 1-3 alkyl; and n is an integer 1 to 5 for use in the treatment of cancer. R 1 is C 1-3 alkyl; R 2 is -NR 2a R 2a' or -OR 2b; wherein one of R 2a or R 2'a is H, and R 2b or the other of R 2a or R 2'a is selected from C 1-6 alkyl, haloC 1-6 alkyl, R 2c R 2'c N-C 1-6 alkyl, carbocyclyl, carbocyclylC 1-4 alkyl, heterocyclyl and heterocyclylC 1-4 qalkyl, wherein any of the carbocyclyl or heterocyclyl groups are optionally substituted by one or more groups selected from halogen, C 1-6 alkyl, haloC 1-6 alkyl, C 1-6 alkoxy, haloC 1-6 alkoxy, carbonyl, -CO-carbocyclyl, azido, nitro and cyano, wherein the -CO-carbocyclyl group may be further optionally substituted by one or more groups selected from halogen, C 1-6 alkyl, haloC 1-6 alkyl, C 1-6 alkoxy, haloC 1-6 alkoxy, azido, nitro and cyano; or two adjacent groups on any of the carbocyclyl or heterocyclyl groups together with the interconnecting atoms form a 5- or 6-membered ring which ring may contain 1 or 2 heteroatoms independently selected from O, S and N; or R 2a and R 2'a together with the N-atom to which they are attached form a 5-, 6- or 7-membered ring which may optionally contain 1 or 2 heteroatoms independently selected from O, S and N; wherein the 5-, 6- or 7-membered ring may be further optionally substituted by C 1-6 alkyl; R 2c and R 2'c are independently H and C 1-6 alkyl; each R 3 is independently selected from H, hydroxy, halo, C 1-6 alkyl, halo C 1-6 alkyl, C 1-6 alkoxy, halo C 1-6 alkoxy, nitro, cyano, CF 3, -OCF 3 and -COOR 5; R 4 is hydroxy, halo, C 1-6 alkyl, halo C 1-6 alkyl, C 1-6 alkoxy, halo C 1-6 alkoxy, nitro, cyano, CF 3, -OCF 3; -COOR 5 or-OS 2 C 1-4 alkyl; R 5 is C 1-3 alkyl; and n is an integer 1 to 5 for use in the treatment of cancer.