PIK3CA and head and neck squamous cell carcinoma: PCT studies of CRCs have validated KRAS mutation as an informative biomarker for cetuximab resistance;21,47 these findings have actually supported revision of the NCCN guidelines for use of cetuximab for CRCs.48 In addition, several PCT studies revealed that mutations in genes including NRAS, BRAF, FGFR1, and PIK3CA (among others) are potential biomarkers for intrinsic resistance to cetuximab in CRCs.8,17,21,49,50 Notably, none of these biomarkers found in CRC PCTs were detected in our HNSCC PCT.