The conditioned medium from both parental human BT549 and MDA-MB-231 (Fig. 3A; Fig. S3), and mouse 4T1 (Fig. 3B) breast tumor cells enhanced invasion of WT breast tumor cells through Matrigel, and this required the presence of DDR2, as this activity was absent when conditioned medium from DDR2-depleted tumor cells was used. Here, DDR2 is linked to breast neoplasm.