In veterinary medicine, alterations in PTEN expression has been investigated in canine melanoma [16], hemangiosarcoma [17], osteosarcoma [18,19], prostate cancer [20], and in canine mammary tumors (CMTs) and feline mammary carcinomas (FMCs) [21,22,23,24] confirming PTEN tumor-suppressor role among different species and neoplasms. Here, PTEN is linked to osteosarcoma.