A compound of formula I: wherein: a is 0, 1, 2 or 3; b is 0, 1, 2 or 3; c is 0, 1 or 2; A is CH or N; the X ring is a substituent on a carbon atom of the sulfur containing ring, and is C 6-10 aryl, a 5 membered heteroaromatic ring containing 1, 2, 3 or 4 heteroatoms independently selected from N, O and S, not more than one heteroatom of which is O or S, a 6 membered heteroaromatic ring containing 1, 2 or 3 nitrogen atoms, or a 7-15 membered saturated, partially saturated or unsaturated heterocyclic ring containing 1, 2, 3 or 4 heteroatoms independently selected from N, O and S; optionally substituted by one or more halogen groups; Y is a direct bond, -O-, >(C=O), >S d, -NR 2 (C=O)- or -(C=O)NR 2 -; d is 0, 1 or 2; R 2 is hydrogen or C 1-6 alkyl; Z is hydrogen, halogen, cyano, hydroxyl, C 1-6 alkyl, haloC 1-6 alkyl, C 1-6 alkoxy, nitro, N(R a) 2; or a ring which is: C 3-6 cycloalkyl; C 6-10 aryl; a 5 or 6 membered saturated or partially saturated heterocyclic ring containing 1, 2 or 3 heteroatoms independently selected from N, O and S; a 5 membered heteroaromatic ring containing 1, 2, 3 or 4 heteroatoms independently selected from N, O and S, not more than one heteroatom of which is O or S; a 6 membered heteroaromatic ring containing 1, 2 or 3 nitrogen atoms; or a 7-10 membered saturated, partially saturated or unsaturated heterocyclic ring containing 1, 2, 3 or 4 heteroatoms independently selected from N, O and S; any of which rings being optionally substituted by one or more groups independently selected from R 3; each R a is independently hydrogen, C 1-6 alkyl, C 1-6 alkylcarbonyl or SO 2 R b; R b is C 1-6 alkyl, amino, C 1-6 alkylamino or di(C 1-6 alkyl)amino; each R 3 is independently halogen, cyano, oxo, hydroxyl, C 1-6 alkyl, haloC 1-6 alkyl, C 1-6 alkoxy, mercaptoC 1-6 alkyl, haloC 1-6 alkoxy, nitro, N(R a) 2, SO 2 R b, OSO 2 R b, COR c, C 1-6 alkylSO 2 R b, R d, C 1-6 alkylR d, C 1-6 alkoxyR d or C 1-6 alkoxySO 2 R d; R c is hydrogen, C 1-6 alkyl or C 1-6 alkoxy; R d is C 6-10 aryl; a 5-membered heteroaromatic ring containing 1, 2, 3 or 4 heteroatoms independently selected from N, O and S, not more than one heteroatom of which is O or S, or a 6 membered heteroaromatic ring containing 1, 2 or 3 nitrogen atoms; any of which rings being optionally substituted by one or more groups independently selected from halogen, C 1-6 alkyl, C 1-6 alkoxy, mercaptoC 1-6 alkyl, haloC 1-6 alkyl, haloC 1-6 alkoxy, amino, C 1-6 alkylamino and di(C 1-6 alkyl)amino; or a pharmaceutically acceptable salt or tautomer thereof, for use in therapy. a is 0, 1, 2 or 3; b is 0, 1, 2 or 3; c is 0, 1 or 2; A is CH or N; the X ring is a substituent on a carbon atom of the sulfur containing ring, and is C 6-10 aryl, a 5 membered heteroaromatic ring containing 1, 2, 3 or 4 heteroatoms independently selected from N, O and S, not more than one heteroatom of which is O or S, a 6 membered heteroaromatic ring containing 1, 2 or 3 nitrogen atoms, or a 7-15 membered saturated, partially saturated or unsaturated heterocyclic ring containing 1, 2, 3 or 4 heteroatoms independently selected from N, O and S; optionally substituted by one or more halogen groups; Y is a direct bond, -O-, >(C=O), >S d, -NR 2 (C=O)- or -(C=O)NR 2 -; d is 0, 1 or 2; R 2 is hydrogen or C 1-6 alkyl; Z is hydrogen, halogen, cyano, hydroxyl, C 1-6 alkyl, haloC 1-6 alkyl, C 1-6 alkoxy, nitro, N(R a) 2; or a ring which is: C 3-6 cycloalkyl; C 6-10 aryl; a 5 or 6 membered saturated or partially saturated heterocyclic ring containing 1, 2 or 3 heteroatoms independently selected from N, O and S; a 5 membered heteroaromatic ring containing 1, 2, 3 or 4 heteroatoms independently selected from N, O and S, not more than one heteroatom of which is O or S; a 6 membered heteroaromatic ring containing 1, 2 or 3 nitrogen atoms; or a 7-10 membered saturated, partially saturated or unsaturated heterocyclic ring containing 1, 2, 3 or 4 heteroatoms independently selected from N, O and S; any of which rings being optionally substituted by one or more groups independently selected from R 3; each R a is independently hydrogen, C 1-6 alkyl, C 1-6 alkylcarbonyl or SO 2 R b; R b is C 1-6 alkyl, amino, C 1-6 alkylamino or di(C 1-6 alkyl)amino; each R 3 is independently halogen, cyano, oxo, hydroxyl, C 1-6 alkyl, haloC 1-6 alkyl, C 1-6 alkoxy, mercaptoC 1-6 alkyl, haloC 1-6 alkoxy, nitro, N(R a) 2, SO 2 R b, OSO 2 R b, COR c, C 1-6 alkylSO 2 R b, R d, C 1-6 alkylR d, C 1-6 alkoxyR d or C 1-6 alkoxySO 2 R d; R c is hydrogen, C 1-6 alkyl or C 1-6 alkoxy; R d is C 6-10 aryl; a 5-membered heteroaromatic ring containing 1, 2, 3 or 4 heteroatoms independently selected from N, O and S, not more than one heteroatom of which is O or S, or a 6 membered heteroaromatic ring containing 1, 2 or 3 nitrogen atoms; any of which rings being optionally substituted by one or more groups independently selected from halogen, C 1-6 alkyl, C 1-6 alkoxy, mercaptoC 1-6 alkyl, haloC 1-6 alkyl, haloC 1-6 alkoxy, amino, C 1-6 alkylamino and di(C 1-6 alkyl)amino; or a pharmaceutically acceptable salt or tautomer thereof, for use in therapy.