MMP9 and head and neck squamous cell carcinoma: Figure 5C shows spheroid cell count having a significant effect on MMP-9 promoter activity in 3D MC HNSCC cells. Here, the MMP-9 promoter activity increased significantly in proportion to the cell number. In contrast, when tumor cells are 3D co-cultured with BMSCs, there was only a small increase in MMP-9 promoter activity in tumor cells depending on the cell number (Figure 5D).