NRG1 and head and neck squamous cell carcinoma: Of interest, the levels of neuregulin (NRG1) expression in PIK3CA mutant Cal27 and HN12 is higher, as compared to parental cells (Fig. 3c), but not in SCC47, an HPV(+) HNSCC cell line, which has high basal levels of NRG1 expression (Supplementary Fig. 5).