In this population , after a median follow-up of 63.8 months , in line with the initial analysis , the addition of cetuximab was associated with numerically higher , but not statistically significant , rates of complete response ( 15.8 % versus 7.5 % , p = 0.31 ) , 5-year progression-free survival ( 75.5 % versus 67.5 % , hazard ratio ( HR ) 0.61 , p = 0.25 ) and 5-year overall survival ( 83.8 % versus 70 % , HR 0.54 , p = 0.20 ) .