Low O6-methylguanine-DNA methyltransferase (MGMT) expression and response to temozolomide in aggressive pituitary tumours. von McCormack, A, McDonald, K, Gill, A, Clark, S, Burt, MG, Campbell, K, Braund, W, Little, N, Cook, R, Grossman, AB, Robinson, BG, Clifton-Bligh, R