These studies in PDAC and ESCC extend the functional role of exosomal miR-21 to mediating pro-metastatic communication between different cell types in the TME (stromal cells to cancer cells) and promoting migration/invasion through pathways involving Ras/ERK/Akt and PDCD4/JNK, further linking exosomal miR-21 to poor prognosis. Here, PDCD4 is linked to esophageal squamous cell carcinoma.