Thymic epithelial tumors in dogs

27 September 2021 – News

Thymic epithelial tumors in dogs

Primary thymic epithelial tumors (TET) are rare in dogs, and little is known about their behavior. There are many recognized human histologic subtypes of TET which have a predictive value in humans but, in veterinary medicine, the classification of TET and their associated prognostic significance has been inconsistent. Therefore, the authors of this retrospective multi-institutional study aimed to determine that.

Fifty-one dogs, with tumors that arose from the cranial mediastinum TET and with a diagnosis bases on histopathology were included. In addition to clinicopathologic data, histology samples were reviewed for the following features: mitotic count, percentage of necrosis, presence of Hassall’s corpuscles, lymphocytic infiltrate, cellular pleomorphism and vascular or capsular invasion. The most common clinical signs were dyspnoea, lethargy and coughing. The most common haematologic and biochemical abnormalities were ionised hypercalcaemia and neutrophilia. In 24.7% of the cases, metastasis was confirmed at the time of the diagnosis and identified as a negative prognostic factor.

Most of the dogs underwent surgical excision of the TET and, in 11.8% of the cases, adjuvant chemotherapy and/or radiation therapy was also reported. Besides the lack sufficient follow-up data, one dog that received COP protocol demonstrated a partial reaction and the dog treated with the CHOP protocol did not show any response. Disease progression was confirmed by diagnostic imaging in all cases.

There was a significant difference between the median survival time of the dogs treated surgically (449 days) and non-surgically (74 days). The survival rate was also significantly higher with dogs with only nodal metastasis, comparing to cases of distant metastasis. Presence of myasthenia gravis, an autoimmune condition recognized as secondary to thymomas in veterinary medicine, was significantly associated with shorter survival. However, the degree of cellular pleomorphism on histology was an independent prognostic factor identified in this study.

Yale, AD, Priestnall, SL, Pittaway, R, Taylor, AJ. Thymic epithelial tumours in 51 dogs: Histopathologic and clinicopathologic findings. Vet Comp Oncol. 2021; 1– 9.