PTGS2 and osteosarcoma: Even though COX-2 expression was found to be upregulated in CSCs isolated from a canine patient with primary osteosarcoma, COX-2 inhibition using meloxicam and mavacoxib did not influence the growth and DR of CSCs in vitro, but it was able to prevent sphere formation from daughter cells, indicating a potential significant role for COX-2 in tumor initiation [39].