Cancer-associated fibroblasts (CAFs) are key factors in the tumor microenvironment, which have been implicated in cancer cell progression. It has also been reported that vesicles called exosomes produced by these CAFs play an important role in cancer progression. A research group investigated the effect of CAF-derived exosomes on the growth of malignant melanoma cells. They found that CAF-derived exosomes express CD9 and CD63 transmembrane proteins, and that the CD9-positive exosomes may inhibit the growth of malignant melanoma cells.