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Melanomas
In Grey Horses May Hold The Clue For Survival In Other Species |
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It is interesting that Tesio in his book,
"Breeding The Race Horse", described the inheritance
of the grey coat color similar to the
inheritance of a disease or defect. On the other hand, the grey horse can
survive melanoma tumors better than any other species that develops them.
While horse owners worry about their grey horse’s tumors, scientists
recognize that the horse must harbor the secret to surviving melanoma.
In the 1970’s I experimented on some otherwise healthy, melanoma-bearing
, retired grey horses by administering autogenous tumor vaccines made by Dr Vincent
Saurino in Boca Raton FL. In one individual horse after receiving a series of
vaccinations made from his own tumor, some areas of skin including the tumors
on his tail lost its black pigment. This is a process called vitiligo. More recent
research shows that it may hold the key to the cure for melanoma.
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Pre-op Melanoma |
I recently met a researcher, Dr John Powderly, whose expertise
on melanoma in several species, including man, has led him to do more work
on immunotherapy and the possible triggering of vitiligo. In mice, man,
horse and a special breed of swine called Sinclair swine, vitiligo has
been associated with melanoma regression.
Sinclair swine are the most dramatic example of the power of vitiligo in the
cure of melanoma. 84% of these miniature, black swine are born with cutaneous
nevi which develop into melanomas within the first six weeks of life. Greater
than 50% of the tumors spread to internal organs. Some of these die by the age
of 6 weeks. Many survive their malignancy as vitiligo begins around 6 months
of age. The tumors then undergo regression. The black pigs turn totally white
as their tumors shrink. Experiments in these swine have shown that the vitiligo
process, though not well understood, is enhanced by hormones and immune competance.
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Post-op |
I have seen unusually developing white skin in horses in response to
hormones, inflammatory insults from infestations to trauma and even post
surgical procedures.
Melanoma-associated-vitiligo and immune mechanisms against pigment cell
antigens occur in the Sinclair swine and the grey horse. If the vitiligo
is a manifestation
of the immune system’s breaking of self-tolerance, then the white patterns
indicate that antigens on melanocytes can be distinguished as targets. In studies
in mice and man, the development of non-pigmented skin occurs in body stripes
which corresponds to a dermatome, or body segment. The striped patterns of vitiligo
suggest unique dermatome-specific antigens. Since melanocytes originate embryologically
at the site of the central nervous system (neural crest), it makes sense to derive
a vaccine from nervous (dendritic) tissue. Dr Powderly is working on development
of a dendritic melanoma vaccine. This is an effort to immunologically turn on
the vitiligo process and achieve regression of the melanoma.
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5 Weeks Post-op |
There have been four documented cases in man of melanoma regression
associated with vitiligo. In all cases vitiligo had crept over the dermatome
where the primary melanoma was situated, and the tumor regressed. These
are rare cases in man, but it is the pattern of regression seen in Sinclair
swine where the vitiligo is generalized.
Vitiligo in the horse is sometimes bilaterally symmetrical and segmental
when it appears to be immune and/or homonally regulated. In my experience
it is not
as common in other coat colors as it is in grey horses, where the pattern is
often random. Although I have not seen spontaneous total regression of melanomas
in the horse as occurs in Sinclair swine, I have seen and had reports of retarded
growth and even partial regression of melanomas in horses that have had some
form of immunotherapy. I have not been aware of the role that vitiligo may play
in the process; however, when I have debulked a rapidly growing melanoma from
the perineum or tail and left it to heal as an open wound, the remaining black
tumor tissue is replaced by healthy pink granulation tissue. Skin then heals
over the pink tissue. I’ve always believed that granulation tissue in the
secondary healing process has an increased immune capability, and it would appear
to be true when granulation tissue replaces melanoma in the grey horse.
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As we anticipate some breakthrough in development
of an immune stimulant in the fight against melanoma in man, we continue
to look to animal models for some clues on the direction the research
should take. Veterinarians will continue to use their tools of immunotherapy
and surgery to enhance the grey horses’ ablity to coexist with
his melanoma. The grey horse perhaps holds the secret to survival from
melanoma for us, his caretakers.
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