We reported that mutated KIT in GIST cell lines accumulated on the trans-side of the Golgi apparatus41 where mutated KIT was phosphorylated on Y703 predominantly, but not on the endoplasmic reticulum (ER).42 Next, we examined the effects of the HSP90 inhibitors on KIT localisation and phosphorylation using confocal microscopy. This evidence concerns the gene HSP90AA1 and gastrointestinal stromal tumor.