XRCC5 and head and neck cancer: In head and neck cancer there are reports of no correlation between expression of DNA-PKcs and the subunits Ku70/Ku86 and in vitro radiosensitivity of explanted tumours (Björk-Eriksson et al, 1999), while in another study tumours with high levels of Ku86 displayed better locoregional control after RT as compared with tumours expressing low levels of Ku86 (Friesland et al, 2003).