A 4.5-year-old Ranchu goldfish (Carassius auratus) presented in May 2015 for evaluation of a slow-growing facial mass of six months' duration. Anesthetized physical exam revealed a 1.5 cm-diameter mass on the left rostral head. The mass was noted to be protruding into the oral cavity with reduction of the lumen by roughly 20%. The mass was also noted to be causing exophthalmia of the left eye. Punch biopsies of the mass were obtained and submitted for histologic analysis. Histologic features of the mass were consistent with a benign myxoma, a tumor previously reported in cyprinids.1 Alcian blue stained the myxoid matrix strongly.
Surgical debulking, intralesional chemotherapy, or radiation therapy were proposed to the owner as potential therapies. The owner elected to pursue palliative intralesional chemotherapy. Several studies have shown promise for treatment of tumors via intralesional administration of bleomycin in veterinary patients2-4 including fish.5 Bleomycin (Cardinal Health) was diluted with saline, then 2.5 U/kg was injected in grid fashion throughout the tumor, utilizing both an intra- and extra-oral approach with the patient under general anesthesia with buffered MS-222. A dose of 0.2 mg/kg meloxicam was also administered IM to control pain and inflammation. The owner reported no adverse effects following administration. Roughly one month after initial bleomycin injection, the owner reported that the tumor had shrunk by roughly 60% of its original size; however, by week 11 post administration, tumor growth was noted once again. Fourteen weeks after initial bleomycin administration, a second intralesional treatment was performed. Mild lethargy was noted during the first 2 days post administration. The owner reported a 20–30% reduction in tumor size following this injection, but once again tumor expansion was noted at 8 to 9 weeks post administration.
At this time, the decision was made to attempt radiation therapy. Due to the owner's financial and time constraints, a dosing regimen of megavoltage radiation delivered in 8 Gray fractions once monthly was selected. For administration of the radiation therapy, the patient was anesthetized with buffered MS-222 on a recirculating system and positioned in dorsal recumbency. Two radiation therapy sessions were performed, and the owner reported no adverse effects following each treatment. However, this dosing regimen was not effective at maintaining the tumor at its initial size, and tumor growth was noted at each monthly visit. The owner elected to euthanize the patient 23 days after the final radiation session due to progressive lethargy and inappetence.
Although these treatment modalities of intralesional chemotherapy and radiation therapy have not been successful at curing disease, they remain potentially useful treatment options that can be used for palliation. Further research into these modalities is needed, as it may be that adjustment of dose and frequency of administration could yield promising results for teleost patients.
The authors would like to thank the doctors, technical staff, and veterinary students of the UC Davis Companion Avian and Pet Exotic Service and the Medical and Radiation Oncology Services for their continued collaboration and excellent assistance in the treatment of this patient.
* Presenting author
+ Student presenter
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3. Kelly JM, Belding BA, Schaefer AK. Acanthomatous ameloblastoma in dogs treated with intralesional bleomycin. Veterinary and Comparative Oncology. 2001;8(2):81–86.
4. Brunner CH, Dutra G, Silva CB, Silveira LM, Monteiro Martins MD. Electrochemotherapy for the treatment of fibropapillomas in Chelonia mydas. Journal of Zoo and Wildlife Medicine. 2014;45(2):213–218.
5. Grosset C, Summa N, Rodriguez Jr. CO, Cenani A, Sheley MF, McCarthy MA, Tanner J, Phillips KA, Hunt G, Groff JM. Excision and subsequent treatment of a leiomyoma from the periventiduct of a koi (Cyprinus carpio koi). Journal of Exotic Pet Medicine; in press.