Clinical, pathologic, and immunohistochemical prognostic factors in dogs with thyroid carcinoma

Background: Prognostic markers for dogs with thyroid tumors are limited. Hypothesis/Objectives: To identify clinical, pathologic, and immunohistochemical prognostic factors for dogs with thyroid tumors. Animals: Seventy dogs with thyroid neoplasia. Methods: Retrospective study. Dogs with thyroid neoplasia were included when follow-up information and formalin-fixed paraffin-embedded tumor samples were available. Immunohistochemistry (IHC) was performed for thyroglobulin, calcitonin, Ki-67, and E-cadherin. Correlation of tumor variables (diameter, volume, localization, scintigraphic uptake, thyroid function, IHC) with local invasiveness and metastatic disease was performed on all tumor samples. Forty-four dogs treated by thyroidectomy were included in a survival analysis. Results: Fifty dogs (71%) had differentiated follicular cell thyroid carcinoma (dFTC) and 20 (29%) had medullary thyroid carcinoma (MTC). At diagnosis, tumor diameter (P=.007; P=.038), tumor volume (P=.020), tumor fixation (P=.002), ectopic location (P=.002), follicular cell origin (P=.044), and Ki-67 (P=.038) were positively associated with local invasiveness; tumor diameter (P=.002), tumor volume (P=.023), and bilateral location (P=.012) were positively associated with presence of distant metastases. Forty-four dogs (28 dFTC, 16 MTC; stage I-III) underwent thyroidectomy. Outcome was comparable between dogs with dFTC and MTC. Macroscopic (P=.007) and histologic (P=.046) vascular invasion were independent negative predictors for disease-free survival. Although time to presentation, histologic vascular invasion and Ki-67 were negatively associated with time to metastases, and time to presentation was negatively associated with time to recurrence, no independent predictors were found. E-cadherin expression was not associated with outcome. Conclusions and Clinical Importance: Prognostic factors have been identified that provide relevant information for owners and clinicians