During a routine physical exam, a 1.2-cm, round, raised, hairless lesion was found on the right thoracic region of the body of an 18-year-old, intact, male, California Sea Lion (Zalophus californianus). After a few weeks of training, a voluntary biopsy of the lesion was taken and sent for histopathology. Histopathologic examination revealed mast cell tumor, and steps were taken for removal.
Under protected contact, the animal allowed surgical excision of the mass with the use of local anesthesia. Rather than close the surgical excision with sutures, the wound was allowed to close using second-intention healing. Histopathologic examination revealed a well-differentiated mast cell tumor with 1 mitosis in 10 HPF limited to the dermis. Clean lateral surgical margins were obtained, but neoplastic cells extended to the deep margin.
In domestic animals, incomplete margins do not guarantee a high rate of local recurrence as previously reported.1,2 Some patients with incomplete excision had no evidence of mast cell disease on histopathology when a second surgery to expand surgical margins was performed. The hypothesis for this occurrence is that the immune system clears the microscopic disease due to inflammation and healing which occurs from the initial surgery.3
Rather than attempt re-excision after the finding of incomplete margins, surveillance and periodic wound cytology were elected. In addition, a full body ultrasound was performed to check for metastasis. Thirty days later, another biopsy of the surgical area was taken, and there was no evidence of mast cell neoplasia. Fine-needle aspirates of the area every 3 months were performed to check for reoccurrence for over a year. After 2 years, there has been no clinical or cytology evidence of recurrence or metastasis in this animal.
The authors thank the staff and trainers at Gulf World by Dolphin Discovery.
* Presenting author
1. Bostock DE. Neoplasms of the skin and subcutaneous tissues in dogs and cats. Br Vet J. 1986;142:1–19.
2. Patnaik AK, Ehler WJ, MacEwen EG. Canine cutaneous mast cell tumor: morphologic grading and survival time in 83 dogs. Vet Pathol. 1984;21:469–474.
3. Murphy S, Sparkes AH, Smith KC, Blunden AS, Brearley MJ. Relationships between the histological grade of cutaneous mast cell tumours in dogs, their survival and the efficacy of surgical resection. Vet Rec. 2004;154:743–746.