Equine melanoma

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Melanomas found under the dock of the tail Grey horse melanoma 2.jpg
Melanomas found under the dock of the tail

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 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]

Contents

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 includes the lymph nodes, spleen, liver, abdominal wall, 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 gray horses

Melanomas found on the lip Grey horse melanoma.jpg
Melanomas found on the lip

Gray horses have a higher susceptibility to melanoma than any other coat color, with up to 80% of gray horses developing some kind of melanoma in their lifetime. [4] Some sources state that up to 66% of those melanomas will become malignant. [3] The gray 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 gray gene is the strongest coat color modifier, and will act on any base color. [5] The gray 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 gray 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 gray horses, which is responsible for the increased incidences of melanoma in horses with the gray gene. [7]

Frequency

One study of gray Quarter horses found that 17.7% had melanomas. The average age of the horses was 9.2 years, and melanomas were much more common in older horses than in younger ones. When split by age, prevalence was 52% in horses over 15 years old compared to 10% in horses under. This is lower than in other breeds and the authors postulate it may have been because only a few of the horses were homozygous for gray, that the chestnut allele of extension may be protective against melanomas caused by gray, or that the breed's genetic background may lower the risk. [10]

In Lipizzaners, 50% of gray horses had melanotic tumors. Divided by age, 56% of horses under 16 years and 94% of horses older were affected. [11]

Types of melanoma

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

Melanocytic nevus

This type of tumor is found in younger horses, around 5 years of age, and is usually benign. They can develop on horses of any color as small single masses, less than 2.5 cm (0.98 in), anywhere on the body. [12]

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. [12]

Dermal melanoatosis

These tumors are frequently malignant and have a high tendency to spread to other organs. They are most commonly found in gray 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. [12]

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-gray horses. [12]

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. [13]

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. [14]

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. [15]

Melanoma vaccine

A vaccine that is similar to the effective canine melanoma vaccine has been created for equine melanoma, [16] and is being studied at the College of Veterinary Medicine at the University of Florida [4]

Related Research Articles

<span class="mw-page-title-main">Skin cancer</span> Medical condition involving uncontrolled growth of skin cells

Skin cancers are cancers that arise from the skin. They are due to the development of abnormal cells that have the ability to invade or spread to other parts of the body. Skin cancer is the most commonly diagnosed form of cancer in humans. There are three main types of skin cancers: basal-cell skin cancer (BCC), squamous-cell skin cancer (SCC) and melanoma. The first two, along with a number of less common skin cancers, are known as nonmelanoma skin cancer (NMSC). Basal-cell cancer grows slowly and can damage the tissue around it but is unlikely to spread to distant areas or result in death. It often appears as a painless raised area of skin that may be shiny with small blood vessels running over it or may present as a raised area with an ulcer. Squamous-cell skin cancer is more likely to spread. It usually presents as a hard lump with a scaly top but may also form an ulcer. Melanomas are the most aggressive. Signs include a mole that has changed in size, shape, color, has irregular edges, has more than one color, is itchy or bleeds.

<span class="mw-page-title-main">Lipoma</span> Benign tumor made of fat tissue

A lipoma is a benign tumor made of fat tissue. They are generally soft to the touch, movable, and painless. They usually occur just under the skin, but occasionally may be deeper. Most are less than 5 cm (2.0 in) in size. Common locations include upper back, shoulders, and abdomen. It is possible to have several lipomas.

<span class="mw-page-title-main">Melanoma</span> Cancer originating in melanocytes

Melanoma is the most dangerous type of skin cancer; it develops from the melanin-producing cells known as melanocytes. It typically occurs in the skin, but may rarely occur in the mouth, intestines, or eye. In women, melanomas most commonly occur on the legs; while in men, on the back. Melanoma is frequently referred to as malignant melanoma. However, the medical community stresses that there is no such thing as a 'benign melanoma' and recommends that the term 'malignant melanoma' should be avoided as redundant.

<span class="mw-page-title-main">Gray horse</span> Coat color characterized by progressive depigmentation of the colored hairs of the coat

A gray horse has a coat color characterized by progressive depigmentation of the colored hairs of the coat. Most gray horses have black skin and dark eyes; unlike some equine dilution genes and some other genes that lead to depigmentation, gray does not affect skin or eye color. Gray horses may be born any base color, depending on other color genes present. White hairs begin to appear at or shortly after birth and become progressively more prevalent as the horse ages as white hairs become intermingled with hairs of other colors. Graying can occur at different rates—very quickly on one horse and very slowly on another. As adults, most gray horses eventually become completely white, though some retain intermixed light and dark hairs.

<span class="mw-page-title-main">Silver dapple gene</span>

The silver or silver dapple (Z) gene is a dilution gene that affects the black base coat color and is associated with Multiple Congenital Ocular Abnormalities. It will typically dilute a black mane and tail to a silvery gray or flaxen color, and a black body to a chocolaty brown, sometimes with dapples. It is responsible for a group of coat colors in horses called "silver dapple" in the west, or "taffy" in Australia. The most common colors in this category are black silver and bay silver, referring to the respective underlying coat color.

<span class="mw-page-title-main">Equine coat color genetics</span> Genetics behind the equine coat color

Equine coat color genetics determine a horse's coat color. Many colors are possible, but all variations are produced by changes in only a few genes. Bay is the most common color of horse, followed by black and chestnut. A change at the agouti locus is capable of turning bay to black, while a mutation at the extension locus can turn bay or black to chestnut.

<span class="mw-page-title-main">Benign tumor</span> Mass of cells which cannot spread throughout the body

A benign tumor is a mass of cells (tumor) that does not invade neighboring tissue or metastasize. Compared to malignant (cancerous) tumors, benign tumors generally have a slower growth rate. Benign tumors have relatively well differentiated cells. They are often surrounded by an outer surface or stay contained within the epithelium. Common examples of benign tumors include moles and uterine fibroids.

<span class="mw-page-title-main">Mastocytoma</span> Medical condition

A mastocytoma or mast cell tumor is a type of round-cell tumor consisting of mast cells. It is found in humans and many animal species; it also can refer to an accumulation or nodule of mast cells that resembles a tumor.

<span class="mw-page-title-main">Neurofibroma</span> Medical condition

A neurofibroma is a benign nerve-sheath tumor in the peripheral nervous system. In 90% of cases, they are found as stand-alone tumors, while the remainder are found in persons with neurofibromatosis type I (NF1), an autosomal-dominant genetically inherited disease. They can result in a range of symptoms from physical disfiguration and pain to cognitive disability.

<span class="mw-page-title-main">Mammary tumor</span>

A mammary tumor is a neoplasm originating in the mammary gland. It is a common finding in older female dogs and cats that are not spayed, but they are found in other animals as well. The mammary glands in dogs and cats are associated with their nipples and extend from the underside of the chest to the groin on both sides of the midline. There are many differences between mammary tumors in animals and breast cancer in humans, including tumor type, malignancy, and treatment options. The prevalence in dogs is about three times that of women. In dogs, mammary tumors are the second most common tumor over all and the most common tumor in female dogs with a reported incidence of 3.4%. Multiple studies have documented that spaying female dogs when young greatly decreases their risk of developing mammary neoplasia when aged. Compared with female dogs left intact, those spayed before puberty have 0.5% of the risk, those spayed after one estrous cycle have 8.0% of the risk, and dogs spayed after two estrous cycles have 26.0% of the risk of developing mammary neoplasia later in life. Overall, unspayed female dogs have a seven times greater risk of developing mammary neoplasia than do those that are spayed. While the benefit of spaying decreases with each estrous cycle, some benefit has been demonstrated in female dogs even up to 9 years of age. There is a much lower risk in male dogs and a risk in cats about half that of dogs.

A vaccine-associated sarcoma (VAS) or feline injection-site sarcoma (FISS) is a type of malignant tumor found in cats which has been linked to certain vaccines. VAS has become a concern for veterinarians and cat owners alike and has resulted in changes in recommended vaccine protocols. These sarcomas have been most commonly associated with rabies and feline leukemia virus vaccines, but other vaccines and injected medications have also been implicated.

<span class="mw-page-title-main">Granular cell tumor</span> Medical condition

Granular cell tumor is a tumor that can develop on any skin or mucosal surface, but occurs on the tongue 40% of the time.

<span class="mw-page-title-main">Cancer in dogs</span>

Cancer is the leading cause of death in dogs. It is estimated that 1 in 3 domestic dogs will develop cancer, which is the same incidence of cancer among humans. Dogs can develop a variety of cancers and most are very similar to those found in humans. Dogs can develop carcinomas of epithelial cells and organs, sarcomas of connective tissues and bones, and lymphomas or leukemias of the circulatory system. Selective breeding of dogs has led certain pure-bred breeds to be at high-risk for specific kinds of cancer.

<span class="mw-page-title-main">Spiradenoma</span> Medical condition

Spiradenomas (SA) are rare, benign cutaneous adnexal tumors that may progress to become their malignant counterparts, i.e. spiradenocarcinomas (SAC). Cutaneous adnexal tumors are a group of skin tumors consisting of tissues that have differentiated towards one of the four primary adnexal structures found in normal skin: hair follicles, sebaceous sweat glands, apocrine sweat glands, and eccrine sweat glands. SA and SAC tumors were regarded as eccrine gland tumors and termed eccrine spiradenomas and eccrine spiradenocarcinomas, respectively. However, more recent studies have found them to be hair follicle tumors and commonly term them spiradenomas and spiradenocarcinomas, respectively. Further confusing the situation, SA-like and SAC-like tumors are also 1) manifestations of the inherited disorder, CYLD cutaneous syndrome (CCS), and 2) have repeatedly been confused with an entirely different tumor, adenoid cystic carcinomas of the salivary gland. Here, SA and SAC are strictly defined as sporadic hair follicle tumors that do not include the hereditary CCS spiradenomas and heridtary spiradenocarcinoms of CCS or the adenoid cystic carcinomas.

Oral pigmentation is asymptomatic and does not usually cause any alteration to the texture or thickness of the affected area. The colour can be uniform or speckled and can appear solitary or as multiple lesions. Depending on the site, depth, and quantity of pigment, the appearance can vary considerably.

<span class="mw-page-title-main">Nevoid melanoma</span> Type of skin cancer

A nevoid melanoma is a malignant neoplastic lesion of the skin. It is a type of melanoma, the most dangerous form of skin cancer. Nevoid melanomas are clinically significant because they are difficult to distinguish from a benign nevus of the skin, which requires no treatment and is common on most individuals. Nevoid morphologies represent up to 3% of all cases of melanoma.

Animal-type melanoma is a rare subtype of melanoma that is characterized by heavily pigmented dermal epithelioid and spindled melanocytes. Animal-type melanoma is also known to be called equine-type melanoma, pigment synthesizing melanoma, and pigmented epithelioid melanocytoma (PEM). While melanoma is known as the most aggressive skin cancer, the mortality for PEM is lower than in other melanoma types. Animal-type melanoma earned its name due to the resemblance of melanocytic tumors in grey horses.

Skin cancer, or neoplasia, is the most common type of cancer diagnosed in horses, accounting for 45 to 80% of all cancers diagnosed. Sarcoids are the most common type of skin neoplasm and are the most common type of cancer overall in horses. Squamous-cell carcinoma is the second-most prevalent skin cancer, followed by melanoma. Squamous-cell carcinoma and melanoma usually occur in horses greater than 9-years-old, while sarcoids commonly affect horses 3 to 6 years old. Surgical biopsy is the method of choice for diagnosis of most equine skin cancers, but is contraindicated for cases of sarcoids. Prognosis and treatment effectiveness varies based on type of cancer, degree of local tissue destruction, evidence of spread to other organs (metastasis) and location of the tumor. Not all cancers metastasize and some can be cured or mitigated by surgical removal of the cancerous tissue or through use of chemotherapeutic drugs.

CYLD cutaneous syndrome (CCS) encompasses three rare inherited cutaneous adnexal tumor syndromes: multiple familial trichoepithelioma (MFT1), Brooke–Spiegler syndrome (BSS), and familial cylindromatosis (FC). Cutaneous adnexal tumors are a large group of skin tumors that consist of tissues that have differentiated towards one of the four primary adnexal structures found in normal skin: hair follicles, sebaceous sweat glands, apocrine sweat glands, and eccrine sweat glands. CCS tumors are hair follicle tumors.

<span class="mw-page-title-main">Mastocytoma in dogs</span> Cancer tumor in dogs

A mastocytoma in dogs is a neoplasm (neoplasia) originating from mast cells in the domestic dog, which occurs mainly in the skin and subcutis. Mastocytoma are not only extremely common in dogs, but also tend to be much more malignant in them than in other animal species. The average survival time for malignant tumors is only four months, whereas for benign tumors it is over two years.

References

  1. ↑ "NADIS - National Animal Disease Information Service -". www.nadis.org.uk. Retrieved 2016-11-26.
  2. ↑ Valentine (2006). "Survey of equine cutaneous neoplasia in the Pacific Northwest". J Vet Diagn Invest. 18 (1): 123–126. doi: 10.1177/104063870601800121 . PMID   16566271. S2CID   34083353.
  3. 1 2 3 Moore, J. S; Shaw, E; Buechner‐Maxwell, V; Scarratt, W. K; Crisman, M; Furr, M; Robertson, J (2013). "Melanoma in horses: Current perspectives". Equine Veterinary Education. 25 (3): 144–151. doi: 10.1111/j.2042-3292.2011.00368.x .
  4. 1 2 3 4 Tannler, B (2013). "Equine Melanoma" (PDF). Equine Health Update. 15: 1–2.
  5. 1 2 3 "Gray Coat Color/ Melanoma". www.horsetesting.com. Retrieved 2016-11-26.
  6. ↑ MacGillivray, Katherine Cole; Sweeney, Raymond W.; Piero, Fabio Del (July 2002). "Metastatic melanoma in horses". Journal of Veterinary Internal Medicine. 16 (4): 452–456. doi: 10.1111/j.1939-1676.2002.tb01264.x . PMID   12141308. Open Access logo PLoS transparent.svg
  7. 1 2 3 Pielberg, 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.; Andersson, L. (2008). "A Cis-acting Regulatory Mutation Causes Premature Hair Graying and Susceptibility to Melanoma in the Horse". Nature Genetics. 40 (8): 1004–1009. doi:10.1038/ng.185. PMID   18641652. S2CID   6666394.
  8. ↑ "Northern Blotting". www.lifetechnologies.com. Retrieved 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. ↑ Teixeira; Rendahl; Anderson; Mickelson; Sigler; Buchanan (2013). "Coat color genotypes and risk and severity of melanoma in gray quarter horses". Journal of Veterinary Internal Medicine. 27 (5): 1201–1208. doi: 10.1111/jvim.12133 . PMID   23875712.
  11. ↑ Fleury, Catherine; Bérard, Frederic; Balme, Brigitte; Thomas, Luc (2000). "The Study of Cutaneous Melanomas in Camargue‐Type Gray‐Skinned Horses (1): Clinical–Pathological Characterization". Pigment Cell & Melanoma Research. 13 (1): 39–46. doi:10.1034/j.1600-0749.2000.130108.x. PMID   10761995.
  12. 1 2 3 4 Valentine, Beth A. (September 1995). "Equine melanocytic tumors: a retrospective study of 53 horses (1988 to 1991)". Journal of Veterinary Internal Medicine. 9 (5): 291–297. doi: 10.1111/j.1939-1676.1995.tb01087.x . PMID   8531173. Open Access logo PLoS transparent.svg
  13. ↑ 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. doi:10.2460/javma.2004.225.94. PMID   15239480.
  14. ↑ 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. doi: 10.2460/javma.229.10.1617 . PMID   17107319.
  15. ↑ Goetz, T. E.; Ogilvie, G. K.; Keegan, K. G.; Johnson, P. J. (1990). "Cimetidine for treatment of melanomas in three horses". J Am Vet Med Assoc. 196 (3): 449–52. PMID   2298676.
  16. ↑ 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. doi:10.1016/j.vaccine.2005.08.027. PMID   16188351.
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