History

A 2-year-old 340-g sexually intact male bearded dragon (Pogona vitticeps) that was a red morph was referred because of a 1-month history of vomiting and regurgitation and a 1-day history of hematemesis. The animal had been mildly lethargic and inappetent after exiting brumation. Blood work performed by the referring veterinarian revealed severe leukocytosis (32.3 X 10³ WBCs/μL; reference range,¹ 1.45 X 10³ to 19.0 X 10³ WBCs/µL) and severe hyperglycemia (1,339 mg/dL; reference range,² 108 to 333 mg/dL). Results were negative for a direct fecal smear and fecal float examination. Radiography revealed loss of coelomic detail, with no evidence of gastrointestinal obstruction (not shown). The bearded dragon was being fed hornworms, Dubia roaches, leafy greens, and squash. Five other bearded dragons were kept in the same household but had no direct access to each other.

Clinical and Gross Findings

At presentation, the animal was quiet, alert, and responsive but slightly lethargic. Physical examination revealed no meaningful findings. Contrast CT revealed a soft tissue–attenuating mass on the lesser curvature of the stomach, with smaller, similar soft tissue–attenuating nodules throughout the hepatic parenchyma. Euthanasia, via IV propofol and pentobarbital, was elected based on a poor prognosis.

Grossly, the animal had appropriate body condition, with ample adipose stores in the coelomic fat pads. The stomach was empty, and a 1 X 1 X 0.7-cm, tan, firm, well-demarcated mass expanded the gastric wall and raised the overlying mucosa (Figure 1), which had multiple pinpoint red foci consistent with ulcerations. The associated area of the serosa had a 1 X 1.2-cm oval depression, with a darker tan outer rim. The liver was diffusely bright yellow and friable, with multiple, 1- to 3-mm-diameter, light tan, firm, well-demarcated nodules randomly distributed throughout the parenchyma. No other meaningful gross tissue alterations were noted.

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Photographs of the gastric mucosa (A) and liver (B) of a 2-year-old 340-g sexually intact male bearded dragon (Pogona vitticeps) with a 1-month history of vomiting, regurgitation, anorexia, and lethargy. A—A raised, well-demarcated mass expands the gastric wall and elevates the overlying mucosa, which has pinpoint dark red ulcerations. B—The liver is diffusely yellow with a light tan, firm, 3-mm-diameter nodule (arrowhead).

Citation: Journal of the American Veterinary Medical Association 260, 10; 10.2460/javma.20.03.0165

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Histopathologic Findings

Histologic examination of the gastric mass revealed a well-demarcated, unencapsulated, densely cellular neoplasm that expanded the gastric submucosa, raised the overlying mucosa, and infiltrated the serosa (Figure 2). The neoplasm was composed of tightly packed acini and nests of polygonal cells, which occasionally formed pseudorosettes, supported by a fine fibrovascular stroma. The neoplastic cells had variably distinct cell borders and a small amount of eosinophilic cytoplasm. Nuclei were oval with finely stippled chromatin and often indistinct nucleoli. The mitotic count was 22/2.37 mm². Anisocytosis and anisokaryosis were moderate, with approximately 5-fold variation in nuclear size. Neoplastic cells invaded blood vessels and lymphatic vessels in the gastric submucosa and serosa. The overlying gastric mucosa was often ulcerated. The surrounding gastric tissue contained few lymphocytes and heterophils. Multiple nodules composed of similar neoplastic cells were scattered throughout the liver. Nuclear pleomorphism was more severe than in the gastric wall, with up to a 10-fold variation in nuclear size. The mitotic count was 21/2.37 mm². Diffusely, hepatocytes were markedly distended by coalescing lipid vacuoles. No other metastases or clinically important histologic findings were observed in other tissues. Approximately 5% of the neoplastic cells in the stomach had strong cytoplasmic immunoreactivity for somatostatin (Figure 3). Neoplastic cells were immunonegative for synaptophysin and chromogranin A. Neoplastic cells in the liver tested negative for all immunomarkers. All positive and negative external (mammalian) and internal control tissues reacted appropriately. Gastric tissue was used as the internal reptilian positive control.

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Photomicrographs of a cross section of the gastric mass (A) and hepatic mass (B) from Figure 1. A—A well-demarcated, unencapsulated, densely cellular mass markedly expands the gastric submucosa, raising and extending into the overlying mucosa and infiltrating the serosa and lymphatic vessels. H&E stain; bar = 2 mm. Inset—Notice that the acini and nests of polygonal cells occasionally form pseudorosettes. H&E stain; bar = 10 µm. B—A moderate number of nodules composed of neoplastic cells, similar to those described in the gastric wall, are scattered throughout the hepatic parenchyma. Hepatocytes surrounding the mass are markedly distended by coalescing lipid vacuoles. H&E; bar = 200 µm. Inset—Neoplastic polygonal cells form nests and acini separated by a fibrovascular stroma. H&E; bar = 60 µm.

Citation: Journal of the American Veterinary Medical Association 260, 10; 10.2460/javma.20.03.0165

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Photomicrograph of somatostatin immunohistochemistry of the gastric mass, showing that approximately 5% of the neoplastic cells demonstrate strong cytoplasmic immunoreactivity for somatostatin. Somatostatin immunohistochemistry; bar = 20 µm.

Citation: Journal of the American Veterinary Medical Association 260, 10; 10.2460/javma.20.03.0165

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Morphologic Diagnosis and Case Summary

Morphologic diagnosis and case summary: gastric neuroendocrine carcinoma (NEC) with hepatic metastasis in a bearded dragon.

Comments

An NEC with hepatic metastasis was diagnosed based on the clinical signs, hyperglycemia, histopathologic findings, and immunohistochemistry (IHC). Gastric NECs are unique epithelial tumors derived from enteroendocrine cells and are commonly reported in bearded dragons.^3–7 Though NECs can arise in many different tissues, gastric NECs are relatively rare in domestic species, with reports mainly in dogs and cats.^8–10 Metastasis is commonly described in bearded dragons, with reported sites including the liver, kidney, lungs, intestine, spleen, oviduct, adrenal gland, and heart.^3–7 In our case, metastases were limited to the liver, one of the most common organs involved in metastatic gastric NECs.⁷ Clinical signs in bearded dragons with gastric NECs are often nonspecific gastrointestinal signs, including regurgitation, diarrhea, anorexia, weight loss, melena, and lethargy.^3–7 Differential diagnoses include gastrointestinal parasitism, foreign bodies, adenoviral infections, constipation, and hepatic lipidosis.⁶ Affected bearded dragons are often ≤ 3 years old,^3–7 similar to the animal of the present report.

Potential clinical diagnostics include routine hematology and serum biochemistry, imaging (such as ultrasonography or CT), fine-needle aspiration biopsy (FNAB), and endoscopic biopsy.³ In this case, both blood work and CT were performed and largely ruled out other differential diagnoses. Clinicopathologic abnormalities, where known, are frequently characterized by hyperglycemia, with variable degrees of anemia and aberrations in WBC counts.^3,4,6,7 This bearded dragon had hyperglycemia and leukocytosis; reported WBC counts are variable, with some animals developing leukopenia rather than leukocytosis.³ In bearded dragons, production of somatostatin presumably inhibits the production of glucose-regulating hormones, including insulin, leading to severe hyperglycemia.^3,4,7 Hyperglycemia is otherwise uncommon in bearded dragons, and diabetes mellitus has rarely been reported in reptiles,¹¹ making it a highly unlikely differential diagnosis for hyperglycemia. Imaging techniques, including CT or ultrasonography, may divulge soft tissue–attenuating masses in the gastric wall or other tissues where metastases occur. In this case, an iodinated contrast agent helped to distinguish normal from neoplastic gastric tissue on CT.

Additional techniques not utilized in this case include FNAB (performed on the liver rather than the gastrointestinal mass due to the risk of gastrointestinal perforation) and endoscopic biopsy. Hepatic FNABs reveal neoplastic epithelial cells in crowded, disorganized clusters with intact bare nuclei, suggestive of a neuroendocrine origin.³ Endoscopic biopsy of the gastric mucosa can also be used, but biopsy of the mucosa overlying a neoplasm may not be diagnostic unless the mass is ulcerated, the sample includes submucosal tissue, or both because these neoplasms are largely limited to the submucosa.⁶

Gastric NECs in bearded dragons form masses in the gastric submucosa, characterized histologically by the formation of acini, nests, and pseudorosettes by polygonal neoplastic cells.^3,4,6,7 The neoplastic cells can have marked nuclear pleomorphism and high mitotic counts, as observed in this case. Invasion into submucosal vessels and metastases to the previously listed tissues are commonly described.⁷ In the animal of the present report, the metastatic lesions had more severe anisokaryosis than the primary gastric tumor, suggesting it was less differentiated. Previous reports^3,7,12 have attempted to classify gastric NECs according to the World Health Organization (WHO) classification scheme in humans. The current WHO classification does not grade human NECs, as they are uniformly high grade by definition¹³; however, WHO classification continues to separate small- and large-cell types of NECs. The neoplasm in this animal was considered a small-cell type. The prognostic importance was unknown, as the prognosis in bearded dragons with this neoplasm is poor.³

Immunohistochemistry is frequently utilized for diagnostic confirmation of neuroendocrine neoplasms. The IHCs performed in this case revealed that approximately 5% of the neoplastic cells were immunoreactive for somatostatin and were not immunoreactive for chromogranin A and synaptophysin. Gastric NECs in bearded dragons are often immunopositive for somatostatin, though neoplastic cells frequently have variable to faint reactivity, suggesting they are most consistent with a somatostatinoma.^3,7 In other reports,^4,7 neoplastic cells are variably immunoreactive for chromogranin A, synaptophysin, gastrin, pancreatic polypeptide, and glucagon, whereas they are immunonegative for neuron-specific enolase, protein gene product 9.6, endorphin, vasoactive intestinal peptide, and insulin. As with most nonmammalian species, failure of mammalian antibodies to cross-react with reptilian tissues can be a challenge with IHC, emphasizing the need for internal positive controls. Additionally, neoplastic cells may have low expression of certain immunomarkers when less differentiated.⁷

Another important histologic finding included severe hepatic lipidosis. Fat deposition in the liver occurs frequently in captive reptiles and can be influenced by the animal’s nutritional status, species, sex, and season.¹⁴ The severity of this animal’s lipidosis was likely multifactorial, resulting from pathologic and physiologic responses associated with the history of inappetence and recent brumation, respectively.

Gastric NECs are unique entities reported with seemingly increasing frequency in young bearded dragons. Clinicians need to be aware of this differential diagnosis for bearded dragons with severe hyperglycemia and nonspecific gastrointestinal signs. Recognition is especially important due to the poor prognosis and high metastatic rate. Potential causes or predisposing factors such as heritable mutations are unknown. In humans, some duodenal somatostatinomas are associated with an autosomal dominant mutation in the tumor suppressor gene NF1, suggesting there may be a potential heritable susceptibility in bearded dragons.¹⁵ Additional research is needed to establish any predisposing factors unique to bearded dragons, possible associations with the morph of bearded dragon, and the prevalence of gastric NECs in these animals.