Hyper-activation of the MAPK and PI3K-AKT pathways is linked to tumour progression in triple-negative breast cancer (TNBC). However, clinically effective predictive markers for drugs targeted against protein kinases involved in these pathways have not been identified. We investigated the ability of MEK and PI3K catalytic activity to predict sensitivity to trametinib and wortmannin in TNBC. MEK and PI3K activities correlated strongly with each other only in cell lines showing woitinannin-specific sensitivity, as shown by a linear regression curve (R = 0.951). Accordingly, we created a new parameter that distinguishes trametinib and wortmannin sensitivity in vitro and in vivo. Our findings suggest that the catalytic activities of MEK and PI3K might predict the response of TNBC to trametinib and wortmannin. (C) 2017 The Authors. Published by Elsevier Inc.