ERBB3 and head and neck squamous cell carcinoma: To further explore the hypothesis that high-level HRG expression defines a sub-population of SCCHN that may be sensitive to agents targeting HER3 and to identify other potential target indications, we evaluated the expression of HRG in large cohorts of patient samples from multiple solid tumor indications and surveyed the activation status of HER3 in SCCHN tumor samples.