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. Here, MMP2 is linked to esophageal squamous cell carcinoma.