Abstract

A 23-year old female Atlantic bottlenose dolphin, Tursiops truncatus, was diagnosed with lingual squamous cell carcinoma (SCC). She was the second in a group of four dolphins housed together to develop oral carcinoma. The first dolphin had a 100-cm³ tumor confined to the frenulum which occupied the entire inter-mandibular space. She has been treated with laser and chemotherapeutic agents. The second dolphin had a history of oral lesions that was first observed 12 years prior to diagnosis. Her oral pathology was typified by numerous lesions (<1mm) on the frenulum that rapidly extended to the tongue surface. These multi-focal lesions went through cycles of waxing and waning for eight years. Approximately four years prior to diagnosis, a pale 1.5x1x1-cm lesion with an irregular border began growing from the left lateral aspect of the tongue. Bacterial and viral cultures of the affected area were non-diagnostic. Blood work was within the normal range, except for a slightly elevated erythrocyte sedimentation rate. Serum titers for viral and fungal panels were negative.

A biopsy of the tongue was performed using a Harmonic Scalpel (Ethicon Endosurgery, Cincinnati, OH) to maximize hemostasis. Tissues were then submitted for histopathology. Additional tissues were submitted for immunohistochemistry, PCR and electron microscopy. Microscopically, atypical squamous cells were seen with infrequent mitoses. The tissue was subsequently classified as a squamous cell carcinoma of low-grade malignancy.

Following diagnosis, an Accuvet 810nm Diode laser (ECS Sharplan Medical Systems, 250 First Avenue, Suite 300, Needham, MA 02494-2814) was used to excise the tumor and to ablate ulcerated surfaces on the frenulum and the tongue. The treatment plan was to perform laser every eight to twelve weeks until all lesions were removed or treated. Follow-up treatments were initiated when re-growth occurred or new lesions developed. Standard laser safety procedures, including protective eyewear and smoke evacuation, were used. Three years post diagnosis, the excised area of the tongue appears normal grossly. Numerous other lesions on the lingual surface, soft palate and on the frenulum have been excised or ablated with laser.

The etiology of oral squamous cell carcinoma in dolphins has recently been attributed to the papillomavirus. Papilloma viruses have been found in wild dolphins and whales as well as in other marine mammals. It is unknown when or why transformation to squamous cell carcinoma occurs, but UV radiation, immunosuppression, injury or irritation to the area may play a role. As all dolphins in this group are affected with oral pathology to varying degrees, it is likely that the virus is infectious, or that these dolphins previously acquired the virus in the wild.

The apparent benign nature of these lesions prior to transformation to SCC may be misleading. They may persist for many years before undergoing malignant change. It is important that biopsies are obtained on oral lesions that persist longer than several weeks. Following diagnosis, lesions should be excised and carefully monitored for reoccurrence.

Acknowledgements

Gregory D. Bossart, Harbor Branch Oceanographic Institute; Ruth Ewing, University of Miami; Louis M. Herman, KBMML/TDI; Adam A. Pack, KBMML/TDI; and Staff and Volunteers, KBMML/TDI