Abstract
Neoplasia in elasmobranchs is rarely reported. In a 2013 retrospective study, there was a 0.4% prevalence of neoplasia in elasmobranchs out of 1546 cases submitted for histopathologic analysis from 1994 to 2010.1 It is unknown whether this low prevalence is due to difficulties in surveillance and sampling of individuals or a true resistance to cancer.2-5 With the increased popularity of elasmobranchs in captivity, as well as the increased risks they are facing in the environment, it is becoming more important to describe diseases affecting these species.
In 2019 and 2020, primary hepatic neoplasia was diagnosed in three adult female bamboo sharks at the Aquarium of the Pacific on postmortem examination. Diagnosis by histopathology was most consistent with biliary carcinoma in two specimens and hepatocellular carcinoma in a third. The sharks were housed in an outdoor, recirculating, natural seawater touch pool at the aquarium for at least ten years prior to death. In case 1, an adult female whitespotted bamboo shark (Chiloscyllium plagiosum) was euthanized in March 2019 due to severe skin papillomas. Incidentally on necropsy, an approximately 4-cm-diameter, pale-tan, firm nodule was identified within the hepatic parenchyma. Histopathology confirmed the diagnosis of this nodule as a biliary adenocarcinoma. In case 2, an adult female brownbanded shark (Chiloscyllium punctatum) was removed from exhibit for decreased nutritional status in October 2019. Ultrasound was suspicious for multiple masses within the hepatic parenchyma. Exploratory surgery was pursued, and several large masses were identified within both lobes of the liver. The patient was euthanized due to poor prognosis. At necropsy, nine firm and mottled hepatic masses were identified, ranging in size from 1 to 6 cm in diameter. Histologic findings included multifocal malignant hepatic neoplasia with a dense scirrhous response and intravascular tumor emboli, most consistent with biliary carcinoma. Multifocal tumor emboli were also noted within the gills. In case 3, an adult female whitespotted bamboo shark was culled when liver masses were detected incidentally on coelomic ultrasound during a routine health screening. Necropsy revealed the presence of two hepatic masses, measuring 1 and 3 cm in diameter, most consistent with a high-grade and poorly differentiated hepatocellular carcinoma on histopathology. Immunohistochemistry was performed in two of these cases, and the results were non-contributary to the diagnosis of neoplasia, presumably due to a lack of cross-reactivity between pan-cytokeratin and the elasmobranch tissues.
In sharks, there are few published reports describing hepatic neoplasia, including a hepatic cholangiocarcinoma in a wild-caught blue shark, a hepatocellular carcinoma in a blue shark, and a hepatic capsular fibroma in a swell shark.4,6 Neoplasia is rarely reported in bamboo sharks, with only one published report of a whitespotted bamboo shark diagnosed with a rostral squamous cell carcinoma.7 To the authors’ knowledge, no reports of primary hepatic neoplasia in bamboo sharks have been published to date. Although rare, clinicians at institutions maintaining these animals should consider primary hepatic neoplasms as differential diagnoses in these species and may consider screening for them during routine examinations.
Acknowledgements
The authors would like to thank all supporting staff at Aquarium of the Pacific, including the veterinary technicians, aquarists, and curators.
*Presenting author
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