H2AX and gastrointestinal stromal tumor: Given that DNA-topoisomerase II inhibitors induce DNA damage, including base damage, single-strand breaks (SSB), double-strand breaks (DSB) and unrepaired or mis-repaired DSBs are lethal and taking into account that γ-H2AX is a common marker of DSBs, we initially examined whether doxorubicin-induced DSBs in GIST remained unrepaired after the inhibition of FGF-signaling.