A 7-year-old female spayed German Shepherd Dog presented to the Cornell University Hospital for Animals’ Oncology Service with the chief complaint of an aggressive bone lesion. The lesion had been diagnosed by her primary care veterinarian one week prior. Upon referral to Cornell, complete staging was performed. A fine needle aspirate was definitive for neoplasia, and a limb amputation was subsequently performed. The limb was submitted for histopathology and was diagnostic for osteosarcoma. Following the limb amputation, the patient was scheduled to receive four doses of carboplatin. Subsequently, the patient is scheduled to begin the osteosarcoma vaccine trial, organized by the Comparative Oncology Trial Consortium in association with the National Cancer Institute/ National Institutes of Health. This vaccine employs immunotherapy for the treatment of canine osteosarcoma. It utilizes an attenuated recombinant L. monocytogenes that expresses the HER2/neu protein in order to activate the host’s adaptive immune response1. The vaccine is still in the trial phase, but early data is promising for prolonged survival in these patients.