“Equine melanoma”的意思、由来-开放百科全书

An equine melanoma is a tumor that results from the abnormal growth of melanocytes in horses. Unlike in humans, melanomas in horses are not thought to be caused by exposure to ultraviolet light.^[1] Melanomas are the third most common type of skin cancer in horses, with sarcoids being the first most prevalent and squamous-cell carcinoma being second.^[2] Melanomas are typically rounded black nodules that vary in size and are usually be found underneath the dock of the tail, in the anal, perianal and genital regions, on the perineum, lips, eyelids, and sometimes near the throatlatch.^[3]

These tumors can be either benign, meaning not cancerous, or malignant, meaning cancerous;^[4] while the benign tumors typically need little treatment to no treatment, the malignant tumors can cause serious problems and can potentially be life-threatening.^[5] Different methods are used to determine if the tumor is malignant and whether it has spread to other organs. Methods used to determine malignancy include fine needle aspirate, biopsy, or complete removal.^[4] To determine if the tumor has metastasized, a rectal examination or an ultrasound can be performed; the most frequent location for metastasis include the lymph nodes, spleen, liver, the abdominal wall, the lungs, and blood vessels.^[6] If the tumor becomes large enough, it can cause weight loss or colic. It may also affect the horse’s ability to turn their head from side to side and eat and drink comfortably if the tumor is on the throat latch area, or cause faecal impaction if tumor is on the anal region.^[3] If melanomas become large and ulcerate, they may become infected.^[5]

Melanoma in grey horses

Grey horses have a higher susceptibility to melanoma than any other coat color, with up to 80% of grey horses developing some kind of melanoma in their lifetime ^[4] and some sources state that 66% of those melanomas will become malignant.^[3] The grey coat color comes from a gene that is responsible for the gradual depigmentation of the horse’s coat; horses with this gene are born darker and over time, they lose their coat pigmentation. The grey gene is the strongest coat modifier, and will act on any base color.^[5] The grey coat color is the result of an autosomal dominant trait that is caused by a 4.6-kb duplication in the 6th intron of the gene syntaxin-17 (STX17).^[7] The region of this mutation contains four genes: NR4A3 (nuclear receptor subfamily 4, group A, member 3), STX17, TXNDC4 (thioredoxin domain–containing-4¢) and INVS (inversin).^[7] To determine what makes grey horses more susceptible to melanomas, researchers have used different techniques such as the Northern Blot technique^[8] and Real-Time PCR.^[9] From these studies, it was concluded that the STX17 gene and the NR4A3 gene are both being over expressed in grey horses, which is responsible for the increased incidences of melanoma in horses with the grey gene.^[7]

Types of melanoma

Not all melanoma tumors are the same; there are four different types of melanomas that can be found in horses.

Melanocytic nevi

This type of tumor is found in younger horses, around 5 years of age, and are usually benign. They can develop on horses of any color as small single masses, less than {{convert|2.5|cm|abbr=on}}, anywhere on the body.^[10]

Dermal melanoma

These tumors are usually benign, but can become malignant over time. They vary in size, and can be found as singles or multiples. They are most commonly found in mature grey horses (less than 15 years old), typically under the tail, around the anus, and on the external genitalia.^[10]

Dermal melanomatosis

These tumors are frequently malignant and have a high tendency to spread to other organs. They are most commonly found in grey horses over the age of 15 as a large coalescing mass under the tail, around the anus, on the external genitalia, or the parotid salivary gland.^[10]

Anaplastic melanoma

These tumors are malignant and frequently spread to other organs. These are rare tumors, typically found in older (more than 20 years of age) non-grey horses.^[10]

Treatment

There are several treatment options when a horse is found to have a melanoma tumor.

Surgical removal

The surgical removal of a melanoma tumor is performed when the tumors are small; this prevents the tumors from spreading to the surrounding areas.^[11]

Intralesional cisplatin

Cisplatin is a chemotherapy drug that is injected into the tumor itself; this drug is commonly used along with surgical removal. That being said, this drug has been shown to resolve tumors with or without surgical removal for at least 2 years.^[12]

Cimetidine

Cimetidine works by slowing tumor growth; it is a histamine blocker that maintains the body’s immune response which aids in the killing of tumor cells. Cimetidine has not been proven to efficiently resolve tumors completely.^[13]

Melanoma vaccine

A vaccine that is similar to the effective canine melanoma vaccine ^[14] has been created for equine melanoma and is being studied at the College of Veterinary Medicine at the University of Florida ^[4]

References

1. ^{{Cite web|url=http://www.nadis.org.uk/bulletins/melanomas-in-horses.aspx|title=NADIS - National Animal Disease Information Service -|website=www.nadis.org.uk|access-date=2016-11-26}}
2. ^{{Cite journal|last=Valentine|first=|year=2006|title=Survey of equine cutaneous neoplasia in the Pacific Northwest|journal=J Vet Diagn Invest.|volume=18|pages=}}
3. ^¹²{{Cite journal|last=Moore|first=J. S|last2=Shaw|first2=E|last3=Buechner‐Maxwell|first3=V|last4=Scarratt|first4=W. K|last5=Crisman|first5=M|last6=Furr|first6=M|last7=Robertson|first7=J|year=2013|title=Melanoma in horses: Current perspectives|journal=Equine Veterinary Education|volume=25|pages=144–151}}
4. ^¹²³{{Cite journal|last=Tannler|first=B|year=2013|title=Equine Melanoma|url=https://vet.purdue.edu/esmc/files/documents/EHUsummer2013singlepg.pdf|journal=Equine Health Update|volume=15|pages=1–2|via=}}
5. ^¹²{{Cite web|url=http://www.horsetesting.com/Equine/Coat_Color/Gray.asp|title=Gray Coat Color/ Melanoma|website=www.horsetesting.com|access-date=2016-11-26}}
6. ^{{cite journal|last1=MacGillivray|first1=Katherine Cole|last2=Sweeney|first2=Raymond W.|last3=Piero|first3=Fabio Del|title=Metastatic melanoma in horses|journal=Journal of Veterinary Internal Medicine|date=July 2002|volume=16|issue=4|pages=452–456|doi=10.1111/j.1939-1676.2002.tb01264.x|pmid=12141308}}{{open access}}
7. ^¹²Pielberg, G., Golovko, A., Sundström, E., Curik, I., Lennartsson, J., Seltenhammer, M., Druml, T., Binns, M., Fitzsimmons, C., Lindgren, G., Sandberg, K., Baumung, R., Vetterlein, M., Strömberg, S., Grabherr, M., Wade, C., Lindblad-Toh, K., Pontén, F., Heldin, C., Sölkner, J., and Andersson, L. (2008). A Cis-acting Regulatory Mutation Causes Premature Hair Graying and Susceptibility to Melanoma in the Horse. Nature Genetics 40(8), 1004
8. ^{{Cite web|url=http://www.lifetechnologies.com/ca/en/home/life-science/dna-rna-purification-analysis/nucleic-acid-gel-electrophoresis/northern-blotting.html|title=Northern Blotting|website=www.lifetechnologies.com|access-date=2016-11-26}}
9. ^Wang, X., Seed, B. (2003). A PCR primer bank for quantitative gene expression analysis. Nucleic Acids Research, 31(24), e154; 1-8
10. ^¹²³{{cite journal|last1=Valentine|first1=Beth A.|title=Equine melanocytic tumors: a retrospective study of 53 horses (1988 to 1991)|journal=Journal of Veterinary Internal Medicine|date=September 1995|volume=9|issue=5|pages=291–297|doi=10.1111/j.1939-1676.1995.tb01087.x|pmid=8531173}}{{open access}}
11. ^Rowe, E.L., & Sullins, K.E. (2004). Excision as treatment of dermal melanomatosis in horses: 11 cases (1994-2000). Journal of the American Veterinary Medical Association, 225(1), 94-96.
12. ^Hewes, C.A., & Sullins, K.E. (2006). Use of cisplatin-containing biodegradable beads for treatment of cutaneous neoplasia in Equidae: 59 cases (2000-2004). Journal of the American Veterinary Medical Association, 229(10), 1617-1622.
13. ^Goetz, T. E., Ogilvie, G. K., Keegan, K. G., and Johnson, P. J. (1990). Cimetidine for treatment of melanomas in three horses. J Am Vet Med Assoc. 196(3), 449-52.
14. ^Bergman, P.J., Camps-Palau, M.A., Mcknight, J.A., Leibman, N.F., Craft, D.M., Leung, C., Liao, J., Riviere, I., Sadelain, M., Hohenhaus, A.E., Gregor, P., Houghton, A.N., Perales, M.A., Wolchok, J.D. (2006). Development of a xenogeneic DNA vaccine program for canine malignant melanoma at the Animal Medical Center. Vaccine, 24(21), 4582-4585.