TLR3 and cancer: Lung epithelial cells are critical for initiating neutrophil recruitment, and the lung metastatic niche is formed by sensing tumor exosomal RNAs via Toll‐like receptor 3 (TLR3).[68, 69] Identification of the metastatic axis of tumor exosomal RNAs and host lung epithelial cell TLR3 activation provides potential targets against cancer metastasis to the lung.[70] Not only tumor‐derived exosomes, but normal cell‐derived exosomes can also be engineered as vectors to target cancer genes.