138PMonitoring the effect of PI3K inhibition on HER2 therapy resistant breast cancer using serial analysis of PIK3CA mutant tumour DNA in plasma. (23rd October 2018) - Keegan, N; Toomey, S; Farrelly, A; Carr, A; Calzaferri, G; Walshe, J; Gullo, G; Crown, J P; Egan, K; Hernando, A; Teiserskiene, A; Grogan, L; et al.