The emergence of bone neoplasms secondary to long-standing osteomyelitis is considered an uncommon and typically delayed outcome in both humans and veterinary patients. We report a case of malignant change—specifically a chondroblastic osteosarcoma—in a 7-year-old German shepherd previously affected by polyostotic osteomyelitis triggered by Serratia liquefaciens at 15 months of age. The neoplasm arose in the right humeral diaphysis, one of the earlier infection sites. To our knowledge, this represents the first documented canine case of polyostotic osteomyelitis linked to Serratia liquefaciens.
