ERBB3 and head and neck squamous cell carcinoma: To determine if high HRG expression was associated with activated HER3 in SCCHN tumors, we performed qRT-PCR for HRG and immunoprecipitation (IP) of total HER3 followed by Western blot for pHER3 and p-Tyrosine in fresh frozen tumor specimens from patients with therapy naïve SCHNN (Figure 1C & D; Table S1).