Outcomes of adjunctive radiation therapy for the treatment of mast cell tumors in dogs and assessment of toxicity: A multicenter observational study of 300 dogs

Abstract

Background Radiation therapy is commonly used as an adjunct to incomplete surgical excision in dogs with mast cell tumors (MCT), but the optimal dose and fractionation regimen have yet to be determined. Hypothesis We assessed outcomes (time to local recurrence, patient survival and toxicity) of a large population of dogs with MCT that received adjunctive radiation therapy. Animals Three hundred dogs with 302 MCT treated using adjunctive radiation therapy. Methods Retrospective observational study. Clinical records of 4 veterinary radiation centers were reviewed. Results Local recurrence rates were similar regardless of radiation protocol with 6.6% of patients developing recurrent cutaneous MCT at a median of 526 days. Local recurrence rate was similar between high and low‐risk MCT. Mast cell tumor related death was reported in 19% of all dogs, with 13% of dogs with low‐risk MCT dying of their disease compared to 29% of dogs with high‐risk MCT. No SC MCT (SCMCT) recurred after radiation therapy and only 7% of dogs with SCMCT were reported to have died of their disease. Mild late toxicity was common in both protocols and severe late toxicity occurred in 1.9% of dogs many years after treatment. Conclusions and Clinical Importance Our study supports the use of adjunctive radiation for the long‐term control of incompletely or narrowly excised cutaneous and SCMCT in dogs. More moderate dose and fractionation protocols may be appropriate in the adjunctive treatment of low‐risk MCT in dogs. Large multicenter prospective studies are required to establish the optimal dose and fractionation for MCT of different risk categories.

Histologic grade has a higher‐weighted value than nodal status as predictor of outcome in dogs with cutaneous mast cell tumours and overtly metastatic sentinel lymph nodes

“…18.19 Scar re‐excision or radiation therapy was offered in the case of incomplete surgical margins; however, reintervention was declined by all owners. Notably, in the low‐grade group only 2 out of 9 (22.2%) dogs with incomplete margins recurred, and this local recurrence rate does not differ much from the one obtained after re‐excision or radiation therapy 17,19 . Conversely, 6 out of 10 (60%) dogs with high‐grade cMCTs and incomplete surgical margins recurred.…”

“…Notably, in the low-grade group only 2 out of 9 (22.2%) dogs with incomplete margins recurred, and this local recurrence rate does not differ much from the one obtained after re-excision or radiation therapy. 17,19 Conversely, 6 out of 10 (60%) dogs with high-grade cMCTs and incomplete surgical margins recurred. This is in accordance with the literature, reporting a significantly higher risk of local recurrence in high-grade cMCTs compared with low-grade tumours with equal surgical margins.…”

“…Second, dogs that did not have adequate tumour control were included in the study. While there is plenty of data supporting that adequate local control improves prognosis, [17][18][19] re-excision of the surgical scar or radiation therapy are not always accepted by owners, thus our population of dogs better reflected daily routine. Also, the two groups were well balanced in terms of completeness of margins.…”

Evaluation of Tumor Grade and Proliferation Indices before and after Short-Course Anti-Inflammatory Prednisone Therapy in Canine Cutaneous Mast Cell Tumors: A Pilot Study

“…The prognosis and subsequent management of the patient after definitive local therapy is dichotomized by the MCT grade. Typically, low-grade tumors require no further treatment, even if incompletely excised, and patients are expected to have good to excellent outcomes, while patients with high-grade tumors are expected to succumb to their disease and require intensive multi-modal therapeutic strategies [1,2,6,[35][36][37][38][39]48,[52][53][54][59][60][61][62][63][64][65][66][67]. This then raises the question of how preoperative glucocorticoid treatment may impact the histological parameters and criteria for grade determination and the immunohistochemical detection of proliferation indices in canine MCTs.…”

Evaluation of Tumor Grade and Proliferation Indices before and after Short-Course Anti-Inflammatory Prednisone Therapy in Canine Cutaneous Mast Cell Tumors

“…The prognosis and subsequent management of the patient after definitive local therapy is dichotomized by MCT grade. Typically, low-grade tumors require no further treatment, even if incompletely-excised, and patients are expected to have good to excellent outcomes; while patients with high-grade tumors are expected to succumb to their disease and require intensive multi-modal therapeutic strategies [1,2,6,[35][36][37][38][39]48,52,55,[60][61][62][63][64][65][66][67][68][69]. This then raises the question of how pre-operative glucocorticoid treatment may impact histological parameters, criteria for grade determination and immunohistochemical detection of proliferation indices in canine MCTs.…”