To further support our findings, we examined the MMP-9 expression in The Cancer Genome Atlas (TCGA) Data Portal from Broad GDAC Firehose to determine whether MMP-9 was involved in the development of head and neck squamous cell carcinoma (HNSCC) and found that MMP-9 exhibits a higher expression in tumours than in various tumours (Figure 6A). This evidence concerns the gene MMP9 and head and neck squamous cell carcinoma.