Influence of treatment on the outcome of dogs with incompletely excised grade-2 mast cell tumors.

In this study we compared the outcomes of dogs with incompletely-excised grade-2 mast cell tumors (incompletely- excised grade-2 MCTs) either adjuvantly treated or not. Dogs with a grade-2 mast cell tumour (MCT) excised either incompletely or with narrow (<5mm) margins, without local recurrence or metastasis at the time of presentation and with a minimum follow-up of 10 months were included in the study. Dogs were separated in 2 groups: treatment (surgery, radiation therapy, chemotherapy or combination of those) and no-treatment. The original excision was incomplete in 90 dogs and narrow in 25 dogs. Ninety-two cases (80%) were treated and 23 (20%) were not treated, but only monitored. Pathology after revision excision found no signs of residual disease in 47/56 cases (84%). Local recurrence was confirmed in 7 dogs, suspected but not confirmed in 2 dogs. Metastatic disease was confirmed in 13 dogs and suspected but not confirmed in 11 dogs. Forty-six dogs died and 69 were still alive at the time of data collection. The 1-yr and 2-yr survival rates were 92% and 82%, respectively. No statistical differences were found regarding disease-free intervals, survival times, recurrence rates, metastatic rates, 1-year and 2-year survival rates between groups, or depending on treatment modality within the treatment group. Based on the finding that the outcome of incompletely-excised grade-2 MCTs was unaffected by adjuvant treatments, this study suggests that immediate systematic adjuvant treatment of incompletely-excised grade-2 MCTs may not be recommended over attentive monitoring and action upon uncommon recurrence.