CD200R1 and neoplasm: While tumor metastasis in vivo differed for 4THM and EMT6 tumors in WT, CD200KO, and CD200R1KO mice (see above), all stromal cells were equally efficacious in promoting the tumor invasion of tumor cells into the matrix, implying a role for stromal cells in tumor invasion, which is independent of the CD200:CD200R axis.