H2AX and gastrointestinal stromal tumor: For example, in the double-strand break (DSB) repair pathway, two genes were modestly (~2-fold) upregulated (Rad51, H2AFX), while four genes were downregulated (ATM, HUS1, RBBP8 and XRCC2) in GIST T1-R cells compared to the parental GIST T-1 cell line.