Canine and Feline Thymic Epithelial Tumors (Thymomas and Thymic Carcinoma)

Thymic epithelial tumors (TETs) are rare neoplasms in dogs and cats, classified as thymomas and thymic carcinomas, with all thymomas considered malignant. These tumors disrupt T-cell development by expressing abnormal major histocompatibility complex class II and autoimmune regulator proteins, leading to autoreactive T cell release and autoimmune disorders such as myasthenia gravis. Clinically, TETs present with respiratory signs and paraneoplastic syndromes. Diagnostic evaluation involves histopathology, immunohistochemistry, and molecular assays. Treatment options include surgical excision, radiation therapy, chemotherapy, and targeted therapy, with surgery offering the best prognosis. This chapter discusses treatment options for TETs, focusing on small molecule inhibitors, immunotherapy, and nutritional support. A sequential approach to small molecule inhibitors is recommended, starting with imatinib, followed by toceranib, and then sirolimus, highlighting their potential to induce remission and manage autoimmune diseases. Immunotherapy, particularly immune checkpoint inhibitors (ICIs), is explored for its promise in treating TETs due to high PD-L1 expression and CD8 + lymphocyte infiltration. However, ICIs are associated with a higher incidence of immune-related adverse events (irAEs) in TET patients compared to other cancers, necessitating further clinical trials to evaluate their efficacy and safety.