Abstract

The Florida Aquarium acquired an adult female Pacific swell shark, Cephaloscyllium ventriosum, from another institution. Although there had been no reports of illness at either facility, it was found dead on exhibit several weeks after arrival. At necropsy, an extremely large (15 cm x 11 cm x 6 cm), creamy white, firm, smooth mass was found extending from the capsular surface of the liver. Histological examination revealed variable numbers of spindle shaped cells with abundant amounts of collagen present in large amorphous aggregates or organized in broad streaming bands. The spindle cells contained slender, oval nuclei with a single prominent nucleolus. Blood vessels were inconspicuous and mitotic figures were absent. The margin between the mass and hepatic tissue was fairly well delineated with occasional clusters of hepatocytes entrapped in the abnormal tissue. The diagnosis was hepatic capsular fibroma. Although fibromas are not malignant tumors, in this case the extremely large size of the mass may have indirectly contributed to the death of the animal.

Contrary to popular belief, sharks do get cancer. However, the number of reported cases in elasmobranchs is small (approximately 30)¹, resulting in the assumption that sharks are relatively resistant to tumor formation. This has led to considerable investigation, as well as misapplication, of potential compounds involved. Shark cartilage proteins and squalamine, an aminosterol from shark liver, have been shown to inhibit tumor angiogenesis^2,4. Squalamine appears to be the most promising candidate for cancer therapy and human clinical trials have been initiated⁶. Cartilage proteins, however, have been found to be fragile and therefore, unconventional cancer treatments such as ingesting shark cartilage tablets are considered to be ineffective.³

Before it can be concluded that elasmobranchs are less likely to develop tumors than other groups of animals, each specimen needs to be evaluated carefully. With greater numbers of animals being kept longer in captivity and with the establishment of thorough necropsy procedures at more facilities, the incidence of tumors identified in elasmobranchs may increase.⁵

Acknowledgements

We would like to thank John D. Strandberg, D.V.M., Ph.D., Dipl. ACVP for his assistance.

References

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2.  Lee A, R Langer. 1983. Shark cartilage contains inhibitors of tumor angiogenesis. Science 221:1185-1187.

3.  Mack A. 1996. Remedies from the deep. Hopkins Medical News, The Johns Hopkins Medical Institutions, Fall:44-47.

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5.  Stoskopf MK. 1993. Neoplasia in sharks. In: Stoskopf, M.K. (ed.) Fish Medicine. W.B. Sanders Company, Philadelphia, PA, Pp. 808-809.

6.  Williams JI. 1998. Squalamine: A new angiostatic steroid. In: Teicher, B.A. (ed.) Antiangiogenic Agents in Cancer Therapy. Humana Press Inc., Totowa, NJ, Pp. 153-174.