A05SQUIRE: a randomised, multicentre, open-label, phase III study of gemcitabine-cisplatin (GC) plus necitumumab (N) versus GC alone in the first-line treatment of patients (pts) with stage IV squamous non-small cell lung cancer (sq-NSCLC); Subgroup efficacy and safety data for pts with epidermal growth factor receptor (EGFR)-expressing tumours