Had completely insensitive variants existed it would have manifest as an accelerated repopulation of the tumour following an initial treatment phase as has been observed by the emergence of resistance to agents such as the V600E-specific b-Raf inhibitors in melanoma (Villanueva et al, 2010) or the EGFRvIII inhibitors in glioma (Sampson et al, 2010). This evidence concerns the gene BRAF and glioma.