1. Auburn University College of Veterinary Medicine
METASTATIC MELANOMA IN A WARMBLOOD MARE
DeAnna Cotton, MPH
Class of 2014
Allison Stewart
BVSc, MS, DACVIM
DACVECC
Fernanda Cesar, DVM
Auburn University College of Veterinary Medicine

2. SIGNALMENT 14 year old Warmblood mare
                       
SIGNALMENT
14 year old Warmblood mare
Presented for radiation therapy and melanoma vaccine

3. REFERRAL HISTORY Aggressive melanoma on the crest of the neck
Metastatic mass within the left prescapular lymph node
Diagnosed as a melanoma 2 months previously
Treatment with oral cimetidine was unsuccessful
Mass had rapidly enlarged and became ulcerated

4. REFERRAL HISTORY Surgical debulking prior to referral
Neoplastic cells extended to the margins

5. CLINICAL FINDINGS Bright, alert, responsive
Normal temperature: (100.2ᵒF)
Pulse: 48 bpm Respiratory Rate: 12 bpm
Weight: 1180 lbs. (536 kg)
Capillary refill time: (<2 seconds)
GI sounds: present in all quadrants
11 cm diameter ulcerated mass on crest of neck
12 cm mass involving left prescapular lymph node
Three 1 cm masses at base of tail

6. Multiple masses in the area of the prescapular lymph node
CONFIRMATION OF DIAGNOSIS
Ultrasound examination to determine the depth of masses and proximity to adjacent structures
Multinodular shoulder mass 5 cm from left carotid artery
Multiple masses in the area of the prescapular lymph node

7. CONFIRMATION OF DIAGNOSIS
Cytology of a fine needle aspirate from the prescapular mass
Neoplastic melanocytes
Spindle shaped with moderate anisocytosis and anisokaryosis

8. FURTHER DIAGNOSTICS No abnormalities were detected on:
Rectal examination
Abdominal and thoracic ultrasound
Abdominocentesis cytology
Thoracic radiographs
Chemistries, CBC, and fibrinogen

9. THERAPAEUTIC PLAN
Surgical removal of the prescapular lymph node was not performed due to the close proximity of the carotid artery
A combination of radiation therapy and melanoma vaccine was recommended for palliative therapy with the hope the mare could return to athletic performance

10. MELANOMA VACCINE
Canine tyrosinase melanoma vaccine Oncept® (Merial Pharmaceuticals)
Once every 2 weeks for 4 doses
Then every 6 months for life

11. ONCEPT® Mechanism of action: The melanocytes over express tyrosinase
Vaccine contains plasmid DNA that expresses the gene coding for human tyrosinase
After injection, the plasmid DNA is taken up by muscle cells which then express the human tyrosinase protein.
An immune response is stimulated toward the melanoma cells which express tyrosinase

12. RADIATION THERAPY Twice a week for 6 treatments
6 Gray applied to each mass
Performed under triple drip general anesthesia after a 12 hour fast
PCV, total protein, and a rebreathing examination were performed prior to anesthesia
No radiation side effects such as skin desquamation or thermal burn occurred

13. Patient under linear accelerator
RADIATION THERAPY
Patient transport
Patient under linear accelerator

14. RADIATION THERAPY Gamma rays damage DNA in chromosomes
Cell death occurs after cells attempt meiosis
Mass reduction occurs over several months
Day of arrival
After 6th treatment

15. LONG TERM MONITORING
Plan involves the referring veterinarian to coordinate with a local veterinary oncologist and continue the melanoma vaccines while monitoring for alterations in mass size
The horse can immediately return to athletic performance

16. STATE OF THE ART TREATMENT
Aggressive radiation therapy and use of the canine melanoma vaccine appears to be a promising treatment combination to potentially control aggressive metastatic melanomas
These treatments work best for microscopic disease, therefore early intervention after radical surgical excision is recommended
Randomized studies to prove the effectiveness of these therapies are required

17. OUTCOME Benefits of radiation and vaccine therapy: Non painful
Throughout radiation and vaccine therapy the mare was not in any discomfort and was able to continue light exercise
Mass reduction should continue over the next 6 months

18. OUTCOME TO BE CONTINUED
Patient being exercised during treatment

19. UPDATE: CREST OF NECK IMPROVED
June 2012
Healing of surgical site
Resolution of mass

20. CREST OF NECK IMPROVED August 2012 No longer ulcerated
Regrowth of hair

21. CONTINUED GROWTH OF PRESCAPULAR LYMPH NODE
June Left picture, seems to be improved
Aug Rt picture, metastasized with smaller nodules surrounding the lymph node.

22. PRELIMINARY CONCLUSION
Horse has continued light work and appears healthy and happy
Primary mass was controlled with surgical debulking and radiation therapy
However, the prescapular mass continues to grow and metastasize
Prognosis is guarded to poor

23. FURTHER READING
1. Fidel, J. Radiation Therapy in Horses: Something to Consider. In Proceedings of ACVIM Conference. San Antonio, TX, June 2008.
2. Fleury, C, Bérard F, Leblond A, Faure C, et al. The study of cutaneous melanomas in Camargue-type gray-skinned horses (2): epidemiological survey. Pigment Cell Res. 2000;13:47–51.
3. MacGillivray, K, Sweeney RW, Del Piero F. Metastatic melanoma in horses. J Vet Intern Med. 2002;16(4):452–456.
4. Phillips, J. Novel Treatments for Equine Melanoma. In Proceedings of ACVIM Conference. Denver, CO, June 2011.