Our results suggest that despite the promising reported characteristics of SNX-ab (Ernst et al. 2014b), [11C]SNX-ab could not be used for quantification of Hsp90α/β expression levels in tumour and brain, considering the insufficient specific Hsp90 binding of [11C]SNX-ab observed in our in vitro experiments and the limited brain exposure shown by our ex vivo/in vivo studies. This evidence concerns the gene HSP90AB1 and neoplasm.