Effect of Strontium-90 on Squamous Cell Carcinoma in an Eastern Box Turtle (Terrapene carolina); Discussion of Alternative Treatment Modalities

Cheryl B. Greenacre, DVM, Dipl. ABVP - Avian and Royce Roberts, DVM, MS, Dipl. ACVR

Department of Small Animal Medicine (Greenacre) and Radiology (Roberts), College of Veterinary Medicine, University of Georgia, Athens, GA 30602

Abstract: An eastern box turtle (Terrapene carolina) presented with a chronic, proliferative, non-healing, ulcerated lesion at the site of a forelimb amputation performed due to trauma 5 years previously. A histopathological diagnosis of squamous cell carcinoma (SCC) was made on biopsy of the affected tissue. Debulking and treatment with Strontium-90 radiation resulted in little clinical improvement. At 5 months after radiation therapy, the tumor had regrown significantly. At necropsy, the tumor was found to be extending into the coelomic cavity near the lung. Recent research has shown that other treatment modalities including radiation therapy, intralesional cisplatin, carboplatin or fluorouracil, and photodynamic therapy may result in complete regression of SCC.

Introduction

Squamous cell carcinoma (SCC) has been diagnosed in reptiles, including chelonians.¹ Chelonian species in which SCC has been reported include a Ceylon terrapin (Geoyda trijuga) and a European pond turtle (Emys orbicularis). Both cases involved the integumentary system, but the pond turtle also exhibited liver metastasis. SCC has also been reported in snakes and lizards involving the oral cavity, cloaca and integumentary system, none of which were reported to have metastasized.¹ No treatments have been documented for SCC in reptiles other than one report of the use of photodynamic therapy in a Boa constrictor with 2 tumors on the lip margin which did not recur after therapy.² The standard therapy for SCC involves surgical excision and/or radiation therapy.

Recently, intralesional cisplatin was shown to completely regress SCC in horses.³  Intralesional carboplatin completely regressed SCC in an Amazon parrot (Amazona ochracephala) and intralesional fluorouracil was shown to completely regress SCC in a Malayan tapir (Tapirus indicus).^3,4,5

Strontium-90 (Amersham International, Arlington Heights, IL.) applications emit beta radiation which effectively treats to a depth of 2-3 mm. The initial activity of the applicator is 55 millicuries and it has an effective treatment diameter of 7-8 mm.

Case Report

An adult, male eastern box turtle (Terrapene carolina) was found on the side of the road and was presented to the University of Georgia Veterinary Medical Teaching Hospital with a mangled left forelimb involving an open, comminuted humeral fracture with severe soft tissue trauma. The limb was amputated under isoflurane anesthesia and recovery was uneventful except for post-operative wound dehiscence at the proximal most aspect of the incision where it met the carapace. The skin had been closed with 4-0 Nylon in a continuous horizontal mattress pattern. The trauma was such that there was little to no skin reserved for suturing along a 1 cm area along the carapace. Over the next several months repeated suturing, Nexaband application and flushing/debriding of the repeatedly dehiscing area were unsuccessful. Eventually, the area formed a scab and thick granulation tissue bed and the area became quiescent until 5 years later when there was sudden rapid growth and ulcerated character to the tissue. A biopsy of the 2 X 2 cm mass showed marked anisocytosis and anisokaryosis of epithelial cells arranged in concentric circles around keratin with large vesicular nuclei, prominent nucleoli and abundant eosinophilic cytoplasm. Frequently the nuclei were very large and irregularly shaped. The changes were consistent with a diagnosis of SCC.

Radiation therapy with Strontium-90 was begun on the affected tissue requiring 4 different fields (7-8 mm each) to treat the affected area. Each field received 20,000 cGy to the surface. One month later the treated area was dryer in character and showed a 75% reduction in ulcerated surface area (Fig. 1).

Fig. 1.  Eastern box turtle 3 weeks after first Strontium-90 treatment for SCC at an amputation site. Only 25% of the pre-treatment ulceration remains.

Two months after the Strontium-90 radiation therapy, 2 areas approximately 1 X 2 cm each showed signs of regrowth and ulceration. A second treatment with Strontiuim-90 (15,000 cGy surface dose per field) was given to 2 areas. One month later there was visible improvement with little to no ulceration (Fig. 2).

Fig. 2. Eastern box turtle 1 week after second Strontium-90 treatment. Ulceration in treated area almost gone. Tissue in affected treatment depth (2-3 mm) is necrotic and has formed a dry scab.

At 5 months after the second treatment, the patient presented with a 5 X 3 cm, very proliferative, ulcerated mass and respiratory difficulty (Fig. 3). The owner elected euthanasia rather than pursuing additional diagnostic or therapeutic procedures.

Fig. 3. Eastern box turtle 5 months after second Strontium-90 treatment showing recurrence of SCC.

The turtle was euthanatized by initially administering an intramuscular injection (0.5 ml) of tiletamine/zolazepam (Telazol, Fort Dodge Laboratories), face mask administration of isoflurane (AErrane, Anaquest, Madison, WI) and then once unconscious, an intracardiac injection (5 cc) of pentobarbital was administered. Necropsy showed the tumor had extended into the coelomic cavity and was acting as a space occupying mass compressing the lungs, but had not invaded the lung tissue. The tumor measured approximately 5 X 5 cm. Histopathology reconfirmed SCC.

Discussion

Since SCC has been linked to previously aggravated tissue, there is the possibility that the constant wound dehiscence, bacterial infection and surgical trauma may have aggravated the tissue and predisposed it to the formation of SCC. There is also the possibility that the original lesion was not induced by trauma, but was an underlying SCC. Histopathologic examination of the amputated tissue was not done.

Strontium therapy in this case was probably not successsful since the affected tissue was thicker than 2-3 mm. The superficial tissue that was in the effective treatment depth (2-3 mm) did regress; therefore Strontium-90 radiation therapy may be useful for relatively small superficial tumors in turtles.

Strontium was used rather than cobalt due to cost and the close proximity of the underlying lung tissue which is more susceptible to radiation therapy. Iridium implants were deemed impractical due to tissue mobility which would have distorted the implants during motion, thus invalidating radiation dosimetry. Currently available literature suggests treatment with intralesional cisplatin, carboplatin or fluorouracil could be attempted and may have resulted in better success, but clients should be fully aware that these drugs are experimental in reptiles and any side affects, including death are possible.

References

1. Bone LB. Neoplasia. In: Mader DR (ed): Reptile Medicine and Surgery. WB Saunders, Philadelphia, 1996,125-141.

2. Roberts WG, Klein MK, Loomis M, et al.: Photodynamic therapy of spontaneous cancers in felines, canines and snakes with chloroaluminum sulfonated phthlocyanine. J Natl Cancer Inst, 1991, 83(1):18.

3. Theon AP, Pascoe JR, Carlson GP, Krag DN. Intratumoral chemotherapy with cisplatin in oily emulsion in horses. JAVMA, 1993, 202(2):261-267.

4. Miller CL, Templeton RS, Karpinski L. Successful treatment of oral SCC with intralesional fluorouracil in a Malayan tapir (Tapirus indicus), J Zoo Wildlife Medicine, 2000, 31(2):262-264.

5. Wilson GH, Graham J, Roberts R, Greenacre CB, et al. Integumentary neoplasms in psittacine birds: treatment strategies. Proc Ann Conf Assoc Avian Vets, 2000, 211-214.

This Page Last Updated October 16, 2000

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