A drop in MMP-2 and MMP-9 activity was detected in addition to its effects on other several apoptotic pathways after quercetin treatment in multiple cancer cell lines i.e., human head and neck squamous cell carcinoma (HNSCC), colon cancer (Caco-2 cells), and breast cancer (MCF-7 cells) [96,97,98]. This evidence concerns the gene MMP9 and head and neck squamous cell carcinoma.