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The Newsletter of the Colorado Herpetological Society

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Veterinary, Medicine, and Health

Reptiles and Cancer

by Kevin T. Fitzgerald, Ph.D., D.V.M.

Medieval anatomists named the disease cancer ("the crab") after its tendency to reach out claw-like, pincer-like, to tissues far removed from its initial sites of origin. Tumor, from the Latin for swollen, was first used in 1597. A tumor is an abnormal proliferation of cells not caused by infection or inflammation. In general, a benign or "good" type of tumor remains localized, is slow-growing and not invasive, has cells recognizable for their tissue of origin, and does not metastasize or spread to distant sites in the body. Malignant tumors are rapidly growing, not well-localized, invasive, cannot be recognized for their tissue of origin, and readily spread through blood, lymph or compression to other locations in the body. A neoplasm, literally a "new growth", has come to mean a tumor and neoplasia is cancer. Many tumor cells lose any physiologic purpose, but some tumor cells retain the function of the original tissue of origin.

A carcinogen is any agent capable of causing cancer. Oncology is the study of cancer as performed by oncologists. As our understanding of cancer clarifies and expands it is becoming apparent that this disease is dependent upon genetic factors, the immune status of the animal, viruses, trauma, radiation, hormones, chemicals, nutrition and various combinations of causative agents. Now that we have briefly defined our terminology, let us examine the incidence and types of tumors seen by veterinarians in captive reptiles.

Many times herpetologists will hear or read that reptiles, like many other lower vertebrates (the shark, for example), enjoy a much lower incidence of cancer than mammals. Be wary of such sweeping and unsubstantiated generalizations. The last fifteen years have produced an astonishing body of documentation of both the appearance and the incidence of tumors in reptiles. Thus, a wide variety of both benign and malignant tumors have been shown to occur in lizards, turtles and snakes. Let us now focus upon those specific tumors that I have seen in private practice over the last 13 years and that have been confirmed by a veterinary pathologist.

Fibromas (benign connective tissue masses), lipomas (benign masses of fat cells), hemanglomas (benign tumors of blood vessel walls) and renal adenomas (benign cystic lesions usually of one kidney) have all been documented in our practice in snakes, lizards and turtles. Boas in particular have been seen frequently with lipomas, but this is perhaps because of their popularity and because we see many boas at our practice. Several iguanas and one box turtle have been presented with growths on the face that when biopsied are reported as benign papillomas, basically the same as warts.

As far as malignant tumors are concerned, these are also encountered in our practice. We have seen fibrosarcoma in Burmese pythons, Reticulated pythons and Boa constrictors, osteosarcoma in a fence lizard, a red-eared slider and a monitor, and adenocarcinoma in the liver of both a monitor and a box turtle. Furthermore, oral carcinomas have been recorded in the gums of one rat snake and one aged box turtle. Finally, we documented a leiomyosarcoma in the intestine of an adult Burmese python.

So statements such as "reptiles appear to have a lower incidence of cancer than other vertebrates" remain unsubstantiated. Professional and amateur herpetologists, zookeepers, veterinarians and pathologists must pool their knowledge to ascertain the actual incidence of cancer in reptiles. For many years, no necropsies were undertaken, no biopsies were done, and no tissue diagnoses were sought from pathologists. It is my impression that the incidence of cancer has been lower in reptiles not because these animals enjoy some inherent protective mechanism, but rather because of the lack of necropsies, biopsies and trained pathological diagnosis. Another complicating factor is a reluctance on the part of the pet-owning public to provide the monetary support to establish such concrete diagnosis. Many owners of obviously sick animals and unwilling to invest the sums necessary to ascertain the source of the animal's problems.

In conclusion, cancer does appear in both captive and in wild reptiles and this is important in and of itself since these animals can serve as models to understand the behavior and trajectory of such tumors in humans and domestic animals. An inter-disciplinary effort must begin among collectors, zookeepers, herpetologists, veterinarians and comparative pathologists in order to obtain comprehensive documentation which would help us to understand cancer more thoroughly not only in reptiles, but also in ourselves and our other fellow creatures.

Kevin T. Fitzgerald, Ph.D., D.V.M.
Staff Veterinarian
Alameda East Veterinary Hospital
9870 East Alameda
Denver, Colorado 80231
(303) 366-2639