HBEGF and head and neck squamous cell carcinoma: To examine whether there is differential expression of EGFR ligands in human tumors, we determined expression levels of TGFA, HB-EGF, NRG1, AREG and EGF by RT-PCR in one normal oral mucosa, two HNSCC tumors taken at the time of diagnosis, and four HNSCC tumors taken at the time of recurrence (Figure 6A and Table 2).