MMP2 and head and neck squamous cell carcinoma: Remarkably, genes such as ERLIN1, MT1M, VAT1, FBN1, MMP2, STAT1, TOM1 and SERPINH1 that were identified as potential metastasis markers in the primary tumor or lymph node microenvironments are cluster markers that are exclusively expressed by CAF populations, thus indicating that CAFs can provide an excellent source of candidates as metastasis biomarkers for HNSCC (Fig. 2e).