Squamous Cell Carcinomas in Inland Bearded Dragons (Pogona vitticeps)

There are an expanding number of reptiles being kept as pet and display animals, and the increasing lifespans of these animals is attributable to a better understanding of their husbandry and nutritional needs, as well as to advancements in veterinary care. As reptiles are living longer, neoplasia is being identified more frequently in these animals. Squamous cell carcinoma (SCC) has been described in many species of reptiles, including lizards, snakes, chelonians, and a tuatara (Ramsay et al., 1996; Garner et al., 2004; Sykes and Trupkiewicz, 2006; Anderson et al., 2010). This case report details the findings of SCC in a bearded dragon (Pogona vitticeps) as well as the findings from a retrospective study estimating the prevalence of this cancer in bearded dragons.

An 8-yr-old male inland bearded dragon presented for evaluation of a mass on the right upper eyelid. The dragon was purchased as a juvenile by the current owner and housed in a 20-gallon (80-L) glass terrarium with newspaper substrate. Light was provided by a fluorescent ultraviolet (UV)-B bulb and a heat lamp, and additional heat was provided by a red incandescent bulb and an undercage heating pad. The lights were left on 12–15 h per day, and the UV bulb was changed approximately every six months. The bearded dragon's daily diet consisted of spinach, carrots, and mealworms, and adult crickets were offered three times per week. The crickets were dusted with powdered calcium and vitamins prior to being offered, but they were not gut loaded. Water was provided fresh daily in a shallow bowl that was too small to allow adequate soaking. The eyelid mass was first noted by the owner two months prior to presentation and continued to grow steadily.

On physical exam, the lizard was noted to be quiet, alert, and responsive. The bearded dragon weighed 440 g and was considered thin, with a body condition score of 3/9. The mass measured approximately 1.5 cm in diameter, and it expanded and effaced the right eyelid and obscured the eye, preventing the eye from being visualized. The mass was ulcerated on the lateral aspect. No other significant findings were noted on the physical examination. A fecal sample was collected via cloacal wash, and no intestinal parasites were noted on a fecal direct smear or flotation. Blood was drawn from the ventral coccygeal vein for a complete blood count (CBC) and in-house plasma chemistry panel (Abaxis VetScan VS1, Abaxis, Inc., Union City, CA). Abnormal findings included an elevated hematocrit, leukocytosis with an absolute heterophilia, elevated aspartate transaminase (AST), mild hyperglycemia, hypophosphatemia, hypopro-teinemia, and hyponatremia (Table 1). The leukocytosis, heterophilia, and hyperglycemia were thought to be secondary to inflammation and infection associated with the mass. The elevated AST was considered to be most likely of muscle origin, but hepatic damage could not be ruled out. Although the dragon was not clinically dehydrated, the elevated hematocrit may have indicated a subclinical dehydration, but the decreased protein and sodium levels were suggestive of adequate hydration or even overhydration. The hypophos-phatemia was not considered clinically significant. An impression smear made from the ulcerated surface of the mass demonstrated erythrocytes, leukocytes, squamous epithelial cells, and a mixed population of bacilli and cocci bacteria.

Dorsoventral and lateral orthogonal radiographs were taken of the body and the head. No abnormalities were noted on the radiographs of the body. On the radiographs of the head, a soft tissue mass could be seen lateral and slightly dorsal to the right orbit, but there was no evidence of skeletal involvement (Figs. 1, 2). Ultrasound of the mass using a 12.5 MHz probe showed it to be a solid soft tissue mass with no cavitations, and the underlying eye appeared to be normal. No invasion of the mass into the globe was noted.

Lidocaine/prilocaine cream (Lidocaine and Prilocaine Cream, 2.5%/2.5%, E. Fougera and Co., Melville, NY) was applied topically to the lateral surface of the mass. Five minutes later, approximately 0.05 mL of 1% lidocaine (1% Lidocaine HCl Injection, USP, Hospira, Inc., Lake Forest, IL) was injected in multiple locations in the mass. Ten minutes after the local anesthetic was delivered, a 4 mm biopsy punch (Biopsy Punch, Miltex, Inc., York, PA) was used to obtain a biopsy from the middorsolateral aspect of the mass. The biopsy site was closed with a single cruciate suture using 4–0 monofilament polydioxanone (Webmax^TM, Webster Veterinary Supply, Sterling, MA). Because of the superficial infection associated with the mass, the bearded dragon was prescribed 10 mg/kg enrofloxacin (compounded in-house using Baytril^® 100 [100 mg/mL, Bayer Healthcare, LLC, Shawnee Mission, KS] diluted to 11.4 mg/mL in a 50:50 mixture of Ora-Sweet^® and Ora-Plus^® [Paddock Laboratories, Inc., Minneapolis, MN]) PO q 24 h. Meloxicam (Metacam^®, 1.5 mg/mL, Boehringer Ingelheim Vetmedica, Inc., St. Joseph, MO) 0.2 mg/kg PO q 24 h was prescribed to manage pain and inflammation. The biopsy from the eyelid mass was submitted and the histopathologic diagnosis was squamous cell carcinoma.

The bearded dragon presented four weeks later for reassessment and surgical removal of the mass. Its body weight had increased to 455 g, and the mass was approximately 50% larger than previously noted (Fig. 3). A CBC and plasma chemistry profile were repeated (Table 1). Abnormal CBC findings included a decrease in the hematocrit and an absolute heterophilia, although the white blood cell count had decreased to a normal level. Abnormal plasma chemistry findings included hypouricemia, mild hyperglycemia, and hypercalcemia.

An intraosseous (IO) cannula was placed in the left tibia, and proper placement was confirmed radiographically. Isotonic crystalloid fluids (Normosol-R^®, Hospira, Inc.) were administered IO at a rate of 3 mL/h. Anesthesia was induced with 10 mg/kg propofol (Propoflo^TM, 10 mg/mL, Abbott Laboratories, North Chicago, IL) administered IO. The dragon was intubated with an uncuffed 2.5 mm ID endotracheal tube (Hudson RCI^®, Teleflex Medical, Research Triangle Park, NC) and maintained on 2.5% isoflurane (Isoflo^®, Abbott Laboratories) and 1 L oxygen with intermittent positive pressure ventilation. Heart rate was monitored by a Doppler probe placed on the ventral thorax. The lizard was placed in ventral recumbency, with the head slightly elevated and rotated to the left using folded surgical towels. The mass was excised with a 5–7-mm margin. Because there was not a sufficient amount of tissue available to reconstruct the eyelid, the eye was subsequently enucleated and the orbit exenterated. The skin was closed with 3–0 monofilament nylon suture (Webster Veterinary Supply). Buprenorphine (Buprenex^® Injectable, 0.3 mg/mL, Reckitt Benckiser Pharmaceuticals, Inc., Richmond, VA) 0.2 mg/kg and ampicillin (Polyflex^®, 250 mg/mL, Fort Dodge, Inc., Overland Park, KS) 22 mg/kg were administered IM perioperatively. Recovery from anesthesia was prolonged, and oxygen was administered via positive pressure ventilation with continued Doppler monitoring for approximately 4 h postoperatively until the lizard could be extubated. Approximately 1 h postoperatively, 0.06 mg/kg atropine (Atropine Sulfate Injection, 1/120 grain, Med-Pharmex, Inc., Pomona, CA) was administered IM because of bradycardia. Following extubation, the dragon was moved to an animal intensive care unit (AICU) heated to 36°C (95°F). IO fluids were maintained at 2 mL/h overnight.

The following morning, the lizard was noted to be depressed, and there was a small amount of serosanguinous drainage from the surgical incision. The animal's hemato-crit was re-evaluated and found to have decreased to 18%; this was attributed to intraoperative hemorrhage and hemo-dilution with IO fluid therapy. The IO fluids were decreased to 1 mL/h and 22 mg/kg iron dextran (Ferrodex^® 100, 100 mg/mL, Agri Laboratories Ltd., St. Joseph, MO) and 0.22 mL/kg vitamin B complex (Vitamin B Complex 150, Neogen Corp., Lexington, KY) were administered IM. Enrofloxacin and meloxicam were administered orally as previously prescribed. Mealworms, crickets, and chopped greens were offered, but the lizard did not eat. Two days after the surgery the lizard was more alert and showing interest in food. IO fluids were discontinued that afternoon, and the IO cannula was removed. The lizard was discharged to the owner with instructions to continue the oral medications as prescribed.

Histologically, the eyelid and associated soft tissues were effaced by a squamous cell carcinoma. The tumor was comprised of anastomosing cords and nests of neoplastic epithelial cells that differentiated from peripheral basal type cells to central squamous cells in a variably ordered fashion with occasional abrupt dyskeratosis, frequently oriented around accumulations of necrotic cellular debris or keratin pearls. The neoplastic cells were noted to have moderate anisokaryosis with large vesicular nuclei, multiple nucleoli, and occasional mitoses. Portions of the tumor were noted to be inflamed or necrotic. No vascular invasion was noted in the examined sections, but tumor cells abutted all examined tissue margins. The eye had some mild cataractous change in the superficial lenticular fibers, mild rhabdomyolysis in the periorbital skeletal muscle, and some mild dilation and hyperplasia of the periocular glands and the harderian gland, presumably as a result of partial obstruction of the duct attributable to the regional neoplastic process. No neoplastic cells were evident in the ocular tissues.

The sutures were removed four weeks postoperatively. The lizard survived for 16 months with no visible evidence of tumor recurrence. When the lizard died, gross examination of the carcass showed no macroscopic evidence of tumor regrowth, but a full postmortem examination was not performed because of severe autolysis.

A review of the records of two zoological pathology laboratories (Northwest ZooPath, Monroe, WA and Zoo/Exotic Pathology Service, West Sacramento, CA, unpublished data) from 2001–2011 identified 12 reports of SCC in bearded dragons, which represented 6% of all neoplasms diagnosed in bearded dragons. On review of these 12 cases, 9 (75%) were noted to have occurred in the eyelids or the periocular tissues. Of the other three (25%) SCCs, one was located on the rostral mandible, one was located adjacent to the vent, and one was on the proximal right rear leg. These findings suggest a predilection of SCCs in bearded dragons in proximity to a mucocutaneous junction (11/12, 91.6%), particularly in the periocular tissues (9/12, 75%).

Additional case information was only available for one (8.3%) of the bearded dragons from the retrospective study. The bearded dragon was treated surgically, and even though the tumor cells extended to the deep margins of the submitted tissue, there had not been any obvious regrowth of the SCC, and the animal was still alive 17 months after surgery at the time of this writing.

Squamous cell carcinoma is a common malignant tumor of the skin and oral cavity of animals. These tumors are typically raised and proliferative but may also present as an erosive lesion (Liptak and Withrow, 2007; Vail and Withrow, 2007). The proliferative lesions can vary from a firm plaque to a more hyperplastic cauliflower-like lesion that is often ulcerative (Vail and Withrow, 2007). Erosive lesions typically start as a shallow crusting that can develop into a deep ulcer (Vail and Withrow, 2007). Histologically these tumors are comprised of nests and infiltrative cords of poorly differentiated squamous cells, occasionally undergoing asynchronous maturation. The cells may form central cores of compressed, laminated keratin, often referred to as “keratin pearls,” or individual cells may be keratinized (dyskeratosis) (Fig. 4). SCCs tend to be locally aggressive and slow to metastasize (Liptak and Withrow, 2007).

In mammals, SCCs typically arise on unpigmented or lightly pigmented skin (Vail and Withrow, 2007). They comprise 15% of cutaneous tumors in cats and 5% in dogs (Vail and Withrow, 2007). In cats, 66% of all eyelid tumors are SCCs, and it is the most commonly documented oral tumor (Miller and Dubielzig, 2007). SCCs in mammals have been linked to exposure to UV light, papillomavirus infection in the dog and cat, and cigarette smoke and tobacco exposure in cats and humans (Liptak and Withrow, 2007; Macy, 2007; Miller and Dubielzig, 2007; Vail and Withrow, 2007).

In reptiles, SCCs are infrequently reported. In a retrospective study of neoplasia in reptiles from the Philadelphia Zoo from 1901 to 2002, the prevalence of neoplasia in reptiles was 2.33% (Sykes and Trupkiewicz, 2006). Of these, 22.4% of the tumors were located in the skin, and 4.1% were SCCs. In that report, neoplasia was documented in 3% of 736 lizard submissions, and 9.1% of those tumors were located in the skin, but the prevalence of SCCs was not noted. In a report of neoplasia in snakes from the Sacra-mento Zoo from 1981–1991, the prevalence of neoplasia was 23.1%, with 10.3% being SCCs (Ramsay et al., 1996). In a retrospective study evaluating neoplasia in lizards from 1994–2002 using pathology reports from Northwest Zoo-Path, the overall prevalence of neoplasia was 6.2%, of which 2.5% were SCCs (Hernandez-Divers and Garner, 2003). In a second study from Northwest ZooPath on neoplasia in reptiles from 1994–2003, the overall prevalence of neoplasia in reptiles was 9.8%, with 4.1% being SCCs (Garner et al., 2004). In this second report, the prevalence of neoplasia in lizards was 8.5%, of which 5.5% were SCCs. The authors also documented that neoplasia was found in 8.6% of agamid submissions, but there were no SCCs reported in that group. A study confined to diseases of the family Agamidae identified neoplastic lesions in 18% of bearded dragon submissions. The most common sites were tumors of the skin or subcutaneous tissues (42%) and included SCCs (Reavill and Schmidt, 2009).

SCC has been reported in multiple species of reptiles. In snakes, it has been documented in the diamondback rattlesnake (Crotalus adamanteus), western gaboon viper (Bitis gabonicrhinoceros), water moccasin (Agkistrodonpiscivorus), Puerto Rican boa (Epicrates inornatus), boa constrictor (Boa constrictor), Argentine boa (Boa constrictor occidentalis), sand boa (Eryx conicus), California king snake (Lampropeltis getula californiae), and Texas rat snake (Elaphe obsoleta lindheimeri) (Roberts et al., 1991; Ramsay et al., 1996; Sykes and Trupkiewicz, 2006; Anderson et al., 2010). In lizards, SCC has been documented in the veiled chameleon (Chamaeleo calyptratus), Jackson's chameleon (Chamaeleo jacksoni), sand lizard (Lacerta agilis), common tegu (Tupinambis teguixin), black-spotted tegu (Tupinambis nigropunctatus), Round Island skink (Leiolopisma telfairii), gila monster (Heloderma suspectum), and leopard gecko (Eublepharis macularius) (Hernandez-Divers and Garner, 2003; Sykes and Trupkiewicz, 2006). In chelonians, SCC has been documented in the loggerhead sea turtle (Caretta caretta), Ceylon terrapin (Geomyda tritugu), European pond turtle (Emys orbicularis), red-eared slider (Trachemys scripta elegans), British Indian turtle (Melanochelys trijuga), spiny soft-shell turtle (Apalone spinifera spinifera), common snake-necked turtle (Chelodina longicollis), yellow-footed tortoise (Geochelone denticulata), Hermann's tortoise (Testudo hermanni), and Eastern box turtle (Terrapene carolina) (Greenacre and Roberts, 2000; Zwart, 2002; Sykes and Trupkiewicz, 2006). There is one report of a SCC in a tuatara (Sphenodon punctatus), and SCC has not been documented in crocodilians.

SCCs have been found primarily in the skin, subcutis, and oral cavity of affected reptiles, but there are a few reports of atypical locations, such as the base of the rattle in a diamondback rattlesnake, the ear canal of a leopard gecko, the intermandibular space of a European pond turtle, and the cloacal mucosa of a tuatara (Ramsay et al., 1996; Sykes and Trupkiewicz, 2006; Anderson et al., 2010). There is also one report documenting a SCC in the periorbital tissues of a veiled chameleon. Metastasis of SCC is rare, but it has been documented in a diamondback rattlesnake, a loggerhead sea turtle, and a European pond turtle (Anderson et al., 2010).

Other tumors that have been documented in bearded dragons include myelogenous leukemia, lymphoblastic leukemia, malignant peripheral nerve sheath tumor, hepatic adenocarcinoma, myxoma, malignant melanoma, malignant chromatophoroma, lipoma, myxosarcoma, poorly differentiated sarcoma, spindle cell sarcoma, chondrosarcoma, bile duct carcinoma, renal carcinoma, gastric neuroendocrine carcinoma, interstitial cell tumor, hemangiosarcoma, hemangioma, thyroid papillary carcinoma, and fibrosarcoma (Suedmeyer and Turk, 1996; Mikaelian et al., 2001; Tocidlowski et al., 2001; Hernandez-Divers and Garner, 2002; Garner et al., 2004; Reavill and Schmidt, 2009; Ritter et al., 2009; Lyons et al., 2010).

Treatment options for SCC in dogs and cats include surgery or cryosurgery (which can be curative with radical excision early in the course of the disease) and radiotherapy (using orthovoltage radiotherapy, strontium 90 plesiotherapy, proton beam radiation therapy, or brachytherapy-198gold seeds) (Liptak and Withrow, 2007; Miller and Dubielzig, 2007; Vail and Withrow, 2007). Other treatment options include photodynamic therapy, chemotherapy (mitoxantrone, actinomycin D, doxorubicin/cyclophospha-mide combinations, bleomycin, cisplatin), or combination therapies, such as intralesional carboplatin with external beam radiotherapy or surgical removal with intralesional cisplatin, 5-fluorouracil, and carboplatin (Roberts et al., 1991; Miller and Dubielzig, 2007; Vail and Withrow, 2007).

In treating SCC in reptiles, surgical excision remains the most commonly reported therapy. However, a boa constrictor with SCC was successfully treated with photodynamic therapy with no recurrence (Roberts et al., 1991). Strontium-90 radiation therapy coupled with surgical debulking was used to treat SCC in an Eastern box turtle, but this regimen was unsuccessful (Greenacre and Roberts, 2000).

In conclusion, the overall prevalence of SCC in reptiles appears to be low. In bearded dragons, there seems to be a predilection for these tumors to occur near a mucocutaneous junction, primarily the eyelid or periocular tissues. In the two cases that were available for follow-up, surgical removal, even with incomplete excision, carried a good prognosis for long-term survival. Because appropriately cared for bearded dragons require a UV light source, additional investigation into a correlation between SCC and UV light exposure may be beneficial in determining whether a cause-effect relationship exists.