While no significant difference in the expression of CXCL12 was observed between subgroups in our classifier, this could be attributed to the fact that increased CXCR4/CXCL12 axis activity was found to be associated with metastasis and recurrence of HNSCC [42]; however, our model is not based on this. Here, CXCR4 is linked to head and neck squamous cell carcinoma.