MMP9 and head and neck squamous cell carcinoma: Among these, group4 (MMP2 and MMP9) was upregulated in nine cancer types, including breast invasive carcinoma (BRCA; diff = 0.86; p = 1.6 × 10−14), lung adenocarcinoma (LUAD; diff = 1.0; p = 3.32 × 10−12), lung squamous cell carcinoma (LUSC; diff = 0.87; p = 1.8 × 10−7), and head and neck squamous cell carcinoma (HNSC; diff = 0.97; p = 5.2 × 10−15).