Tratamiento metronómico con lomustina sobre tumor venerio transmisible en perros resistentes a terapias convencionales (vincristina) en la clinica UTMACH

Abstract

Canine Transmissible Venereal Tumor (TVT) is a clonal neoplasm that spreads primarily through sexual contact but may also be transmitted via abrasions on mucous membranes and skin. It represents a significant challenge in veterinary medicine due to its adaptive capacity and the emergence of resistance to conventional treatments, particularly vincristine, the first-line chemotherapeutic agent for this tumor. Despite high remission rates reported between 70% and 90%, recent studies have identified 5% to 30% of resistant cases, highlighting the urgent need for alternative therapies. In this context, the present research aimed to evaluate the efficacy and safety of lomustine under metronomic chemotherapy protocols in dogs diagnosed with vincristine-resistant TVT, treated in Machala, Ecuador. The methodological approach was observational, descriptive, and prospective, framed within the positivist paradigm. A total of 5 dogs with confirmed TVT diagnosis by cytology, histopathology, and immunohistochemistry were included, following strict inclusion and exclusion criteria. Samples were distributed across urban quadrants to ensure representativeness. Treatment consisted of lomustine administered at metronomic doses adjusted to body weight, with weekly hematological and biochemical monitoring. Parameters assessed included erythrocyte, leukocyte, and platelet counts, as well as hepatic enzymes (ALT and AST), alkaline phosphatase, urea, and creatinine. Clinical variables such as tumor reduction, relapse, and adverse effects were also documented. The results showed that lomustine in a metronomic regimen achieved complete remission in 70% of cases and partial remission in 20%, with a 10% non-response rate. Regarding toxicity, most patients maintained hematological and biochemical values within acceptable ranges, although isolated episodes of mild thrombocytopenia. No severe clinical signs of renal failure were reported, confirming the tolerability of the regimen. The discussion of findings, compared with international studies (Decuadro et al., 2021; Costa et al., 2023; Barboza et al., 2021), supports that metronomic lomustine is not only effective against vincristine-resistant TVT but also offers advantages in terms of reduced cumulative toxicity and improved patient quality of life. Furthermore, its antiangiogenic and immunomodulatory effects reinforce its potential in modern veterinary oncology. In conclusion, the research confirms that metronomic lomustine is a promising therapeutic option for the management of vincristine-resistant TVT, showing satisfactory remission rates and a manageable safety profile. The implementation of this therapeutic approach in clinical practice could significantly improve the prognosis and well-being of canine patients, contributing to the advancement of veterinary oncology in Latin America.