Spontaneous Regression and Reoccurrence of Osteosarcoma in a Canine Tibia

Abstract

A 32-month-old female Labrador Retriever mix-breed presented for right pelvic limb lameness with firm swelling on the lateral aspect of the stifle. Radiographs revealed a mass with periosteal elevation along the lateral cortex of the proximal tibia. Histology on a core biopsy sample was diagnostic for osteosarcoma. Surgical treatment was declined. Eight months post diagnosis, the patient was re-evaluated by the primary care veterinarian and had no lameness, pain, or tibial swelling. Sixty-three months later (5.2 years), the patient presented for cranial cruciate ligament ruptures. Radiographs revealed a smooth bony protuberance on the lateral aspect of the right proximal tibia in the area of the previous osteosarcoma. The patient underwent bilateral tibial plateau levelling osteotomies. The surgical recovery was uneventful with normal healing. Twenty-seven months following surgery, the patient returned for painful swelling around the right proximolateral tibia. Radiographs revealed an 8 × 9 cm osteoproliferative and osteolytic lesion of the proximal tibia. Osteosarcoma was confirmed via core biopsy. The bone tumour grew rapidly, and the patient was euthanatized 3 months thereafter. This case report demonstrates the unusual occurrence of an osteosarcoma in a young dog which spontaneously regressed. Ninety months (7.5 years) after clinical resolution of the initial tumour, osteosarcoma formed again in the same location. Lifetime patient monitoring with repeated clinical exams, serial radiographs, and multiple biopsies by the same surgeon, pathologists, and radiologist are unique features of this case report.