MMP9 and head and neck cancer: The results showed that SPP1 was over-expressed in patients with head-neck cancer, and the top 3 genes co-expressing with SPP1 were Matrix Metallopeptidase 9 (MMP9), Actin Related Protein 2/3 Complex Subunit 1B (ARPC1B) and Amyloid Beta Precursor Protein (APP) (Fig.8 a).