Knockdown of STAT1 in SCC61 causes tumour growth suppression and radio sensitization. In untreated tumours, STAT1 [Signal Transducer and Activator of Transcription 1] knockdown (KD/C; white diamond) significantly reduced day 40 tumour volume by 2.7-fold compared to a control-vector transfected STAT1 wild-type (WT/C; black diamond) (mean ± standard error of mean [SEM] [mm3]: WT/C = 1154 ± 404, KD/C = 427 ± 130; Student's t-test P = 0.050). Ionizing radiation (IR) was delivered in 5 Gy fractions on days 0-5 (total 30 Gy). In irradiated tumours, KD of STAT1 (KD/IR; white triangle) significantly suppressed day 68 tumour volume by 6.5-fold compared to that of a STAT1 WT tumour (WT/IR; black triangle) (mean ± SEM [mm3]: WT/IR = 738 ± 232, KD/IR = 114 ± 21.2; Student's t-test P = 0.017). Point, mean tumour volume; error bars, SEM. Tumour volumes are shown on a semi-log scale.