AGR2 and head and neck squamous cell carcinoma: In addition, our previous data have proved that C4.4A and AGR2 were activated in SCCHN and associated with EMT or CSCs 39, 44; moreover, both of them have a strong correlation and a similar expression pattern with TRAF6 (C4.4A, P < 0.01, r = 0.3694; AGR2, P < 0.001, r = 0.4107; Fig. 5B and C).