TUMORS IN REPTILES

• INTRODUCTION

Tumors or neoplastic lesions are common in reptiles. The incidence of the disease in this class is comparable with that of mammals and birds. The highest prevalence occurs in snakes, followed by lizards while it is relatively low in turtles and tortoises. Several factors have been identified to predispose tumor development in reptiles, such as viruses, genetic predisposition, and hormonal alterations. Contrary to older beliefs, which suggested that cancers are rare in reptiles, more systematic analysis and longitudinal studies have noted that cancers in reptiles have an overall prevalence of 9.8%.

• ETIOLOGY

Although most tumors in reptiles are spontaneous in origin, several viruses have been identified for their carcinogenic potential in association with tumors. In fact, factors predisposing to tumor development in reptiles continue to be elucidated. A genetic predisposition is suspected in several recent reports of genetically related reptiles. Hormone profile alterations may also predispose reptiles to neoplastic disease.

Turtles and tortoises have a relatively low incidence of neoplasia (10.3%) and possibly a lower than expected incidence of metastasis. Indeed, thyroid adenocarcinoma is the most commonly reported single tumor of endocrine origin reported in chelonia.

Snakes are the class of Reptilia most commonly reported as affected by neoplasia. In fact, the hematopoietic and lymphoid systems are most commonly affected, followed by neoplasia of epithelial origin.

Lizards have a median incidence of neoplastic disease compared with snakes, turtles, and tortoises, and the lymphoma is the most commonly reported single neoplasia of lizards.

• DIAGNOSIS

At present, history, physical examination, clinical pathology, imaging, and microscopic evaluation are minimum requirements. Neoplasia is more common in older reptiles, but has been described in young animals, such as monitor lizards as young as 5 months of age.

The differential diagnosis for a mass in a reptile is similar to those of companion mammals and include inflammatory diseases such as abscesses, granulomas (parasitic, fungal, protozoal, or bacterial), nutritional deficiencies such as hypovitaminosis A. Complete blood count and plasma biochemistry results can be used to determine the relative health of the patient, to identify systemic manifestations of disease, and for surgical planning.

Radiography and ultrasonography are the most widely used imaging tools for reptilian patients. Advanced imaging such as computed tomography and MRI are becoming more widely used in reptile medicine. Endoscopy can be used in reptiles to assess internal structures and obtain samples for diagnosis. In fact, biopsy of lesions is indicated to determine underlying neoplastic or other cause. Eventually, microscopic evaluation of tumor types is an important step in the diagnosis of neoplasia and to differentiate neoplastic processes from infectious or inflammatory causes.

• TREATMENT

As ectotherms, reptiles affected by neoplasia further require excellent husbandry to include diet, appropriate humidity, and optimum temperature zones.

Surgery is a commonly used and effective means to treat neoplasia and is often curative in cases with easily accessible and resectable tumors. Although, the most common neoplastic complications of surgical intervention are recurrence of the neoplasm at the surgical site, infection, and metastasis.

Chemotherapy involves the application of a chemical agent that targets and damages neoplastic and proliferative tissue. Chemotherapeutic efficacy and appropriate dosing regimens for reptiles remain minimally investigated and poorly understood. As with mammalian patients, chemotherapy carries the risk of immunosuppression. Therefore, frequent monitoring of complete blood counts in reptile patients undergoing chemotherapy is required. Prophylactic antibiotic therapy may be administered to prevent bacterial infections of the patient secondary to the immunosuppressive effects of chemotherapy.

Electrochemotherapy has provided acceptable reptile patient outcomes, including fibropapillomas of green sea turtles. This therapy is likely to provide the best outcomes for patients with tumors that are benign or that have a low risk of metastasis because its effects are limited to localized disease. However, based on the administration of the electrical pulses, electrochemotherapy is considered painful and thus analgesia, heavy sedation, and/or anesthesia must be provided

• SUPPORTIVE CONSIDERATIONS FOR REPTILE PATIENTS WITH NEOPLASIA

As ectotherms, immune response depends on providing the appropriate temperature gradient. As prey species, appropriate places for rest, sleep, and unencumbered natural behaviors must be provided. Hydration and nutrition must be provided in order to obtain the best effects of the drugs and treatments administered. Analgesia and antibiosis must also be carefully considered in these species.

For outpatient analgesia, enteral medications such as tramadol and nonsteroidal anti-inflammatory drugs are commonly used. Nutritional support of oncology patients is of paramount importance regardless of species.

IMAGES

REFERENCES:

• De Santi, M., Cruz, N., Barranco, G., Lima, G., Menezes, M., Matiz, O. S., ... & Werther, K. (2020). Cutaneous melanoma in a red-footed tortoise (Chelonoidis carbonaria). Journal of Exotic Pet Medicine, 34, 44-47.

• Christman, J., Devau, M., Wilson-Robles, H., Hoppes, S., Rech, R., Russell, K. E., & Heatley, J. J. (2017). Oncology of reptiles: diseases, diagnosis, and treatment. Veterinary Clinics: Exotic Animal Practice, 20(1), 87-110.

• Divers, S. J., & Stahl, S. J. (Eds.). (2018). Mader's Reptile and Amphibian Medicine and Surgery-E-Book. Elsevier Health Sciences.