predicting patterns of mutations arising during drug therapy using in vitro mutagenesis screen in cells, isn't a new method and has been used before for other drugs
Agreed, but it's the first time it's been used on this particular pathway, and so its predictive ability here was relatively unknown. So the fact that it was in fact predictive here gives me more confidence in its predictive power with respect to the Ariad drug. Extrapolating from preclinical to clinical is never a given.