MMP9 and head and neck squamous cell carcinoma: Moreover, a co-expression analysis of a subset of the HNSCC database (530 samples) of the TCGA project using the cBioPortal website revealed a significant positive correlation between PKM2 and GLUT1, HK2, LDHA, MMP-2, MMP-9, and MMP-13 (Supplementary Figures S3 and S4) [24].