Case Report

Submitted by Olivia Obringer, Michigan State University

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 reevaluated 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 proximo-lateral tibia. Radiographs revealed an 8x9 cm osteoproliferative and osteolytic lesion of the proximal tibia. Osteosarcoma was confirmed via core biopsy. The bone tumour grew rapidly, and the patient was euthanised 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.

FIGURE 1 Orthogonal right stifle radiographs of a 32-month-old canine female revealing a smooth periosteal elevation and bony reaction on the lateral tibial metaphysis. 

FIGURE 6 Orthogonal right stifle radiographs 24 months following the tibial plateau leveling osteotomy, revealing an osteolytic and productive lesion of the right proximal tibia. 

FIGURE 7A Histopathology figure (20x magnification) from the right tibial bone biopsy revealing tumor cells with areas of osteoid deposition (stars) as well as some chondroid matrix (#).

FIGURE 7B Histopathology figure (400x magnification). The neoplastic tissue consists of spindled to polygonal cells with nuclear atypia and high mitotic count consistent with high-grade osteosarcoma. Osteoid production is closely associated with the neoplastic cells.