GDNF and osteosarcoma: Compared to normal canine osteoblasts, six genes were significantly (adjusted p < 0.05) under-expressed in the aggressive tumors: GDNF,CEMIP (KIAA1199), GDF6, ALPK2, GREM1, and DHRS2. CEMIP is a target gene of the Wnt/β-catenin signaling pathway and is known to promote cancer cell migration [26–28]; it is thus surprising that all four canine osteosarcoma specimens – aggressive and non-aggressive – demonstrated marked and significant under-expression compared to normal osteoblasts.