Prognostic Impact of a Histologic Grading Scheme in Dogs Diagnosed With Rib Chondrosarcoma

Data regarding the outcome of canine rib chondrosarcoma is sparse and varied. While grade of tumour is associated with outcome for canine appendicular chondrosarcoma, the association of grade with outcome for canine rib chondrosarcoma is unclear. This study aimed to correlate the grade of canine rib chondrosarcoma with median survival time. Retrospectively, cases of primary rib chondrosarcoma were identified, and tumours were graded based on a 3-tier adapted human grading scheme. Twenty-two patients were included in the survival analysis. The median survival time was 1427 days (range: 27-3354 days). This was not significantly different for patients with grade I versus II versus III (p = 0.82), grade I-II versus III (p = 0.34), or grade I versus II-III (p = 0.49). No variables assessed including age, weight, tumour location (cranial vs. caudal thorax; left vs. right hemithorax), tumour location on rib (proximal, middle, and distal), radiographic appearance (lytic, proliferative, or mixed), elevated serum alkaline phosphatase activity, grade, grade specific histologic features (matrix production, architecture, pleomorphism, cellularity, necrosis, and total score), adjunct therapy post-surgical excision, development of metastatic disease post-surgery, or local recurrence post-surgery were found to impact the risk of death due to chondrosarcoma. In this limited group of patients, the grading scheme reported here, and the other variables assessed did not appear to offer additional prognostic information. However, this data must be interpreted considering the small sample size and thus low statistical power. Additional studies are needed to determine the true impact of grade on outcome for canine rib chondrosarcomas.