The invention provides a compound of formula (0): or a pharmaceutically acceptable salt, N-oxide or tautomer thereof; wherein: n is 1 or 2; X is CH or N; Y is selected from CH and C—F; Z is selected from C—Rz and N; R1 is selected from: -(Alk1)t-Cyc1; wherein t is 0 or 1; Optionally substituted C1-6 acyclic hydrocarbon groups R2 is selected from hydrogen; halogen; and C1-3 hydrocarbon groups optionally substituted with one or more fluorine atoms; R3 is hydrogen or a group L-R7; R4 is selected from hydrogen; methoxy; and optionally substituted C1-3 alkyl; and R4a is selected from hydrogen and a C1-3 alkyl group; wherein Rz, Alk1, Cyc1, L1 and R7 are defined herein; provided that the compound is other than 6-benzyl-3-{2-[(2-methylpyrimidin-4-yl)amino]pyridin-4-yl}-7,8-dihydro-1,6-naphthyridin-5(6H)-one and 3-{2-[(2-methylpyrimidin-4-yl)amino]pyridin-4-yl}-7,8-dihydro-1,6-naphthyridin-5(6H)-one and salts and tautomers thereof. The compounds are inhibitors of ERK1/2 kinases and will be useful in the treatment of ERK1/2-mediated conditions. The compounds are therefore useful in therapy, in particular in the treatment of cancer.