MMP9 and esophageal squamous cell carcinoma: Besides MMP2 and MMP9 discussed above, MDK 12 and interleukin-1β (IL-1β) 14 were also not detected in SRGN Exo of ESCC cells (Table S3) even though MDK was found in exosomes derived from melanoma cells 46 and neuroblastoma cells 47.