charlie
14th Aug 2001, 09:00 AM
RE: the arab, wouldnt let me post a reply, so posted new message.
Could be a melanoma, common for greys, especially arab types.
(didnt the vet take any tests etc)anyway:
Miserable Melanomas
Every owner of a gray horse lives in fear of melanomas, those characteristic black or brown nodules that so often appear on the skin around and under the tail. Rightly so, for estimates suggest that more than 80% of gray horses over the age of 15 will develop at least one melanoma tumor during its lifetime. The “why” hasn’t been determined. We know that melanomas are tumors of the melanocytes, the cells that produce skin pigment. We know that in aging gray horses there appears to be a disturbance in the metabolism of melanin, which stimulates local over-production of dermal pigment. But why gray horses are particularly susceptible isn’t yet clear. (One thing is reasonably certain—unlike melanomas in humans, which might be triggered by overexposure to ultraviolet radiation, gray-horse melanomas don’t appear to be linked to an overdose of sun. The shady locations in which they tend to develop, and the fact that the skin of gray horses is black, and thus well-protected from U/V radiation, attest to this.)
Melanomas can be hard or soft, solitary or appearing in clusters. Often, they’re subcutaneous when they first appear, covered by normal skin, but as they develop over time, they become more obvious, and their surfaces can become ulcerated and/or infected. Although they’re generally dark brown, gray, or black in color, it’s also possible for these tumors to be unpigmented (amelanotic), a situation which makes diagnosis considerably more challenging (microscopic examination of biopsy samples being the only way to identify these “invisible” tumors).
The underside of the tail, the perineal and peri-anal regions, and the penis and sheath in males are the most common locations for melanomas to sprout. They also can be found on the ear margins, elsewhere on the head, in the jugular region, and near or on the parotid salivary gland. It’s quite possible for melanomas to spread internally as well, most commonly gravitating to the serosal surfaces of the liver, spleen, and lungs.
Much of the time, melanomas are fairly benign, slow-growing tumors, and are more unsightly than dangerous. They might remain that way for years or even decades. Within each tumor, however, lurks the potential for an overnight change to malignant growth, which swiftly can change the situation from a cosmetic nuisance into something life-threatening.
They might appear as rapidly spreading series of lumps or nodules, or even as vast, rippling sheets of black tumor masses across the tissue. Malignant melanomas can interfere with a horse’s excretory functions, with breeding and foaling, or, if found in other locations on the body, such as the back or neck, with working under saddle or in harness.
Because malignant melanomas frequently appear in multiple sites, and because they have a high rate of metastasis, they can be very difficult to cure. Gray horses aren’t the only ones affected; horses of other coat colors also can develop melanomas. The incidence in non-grays is much lower, but when melanomas do appear in these horses, the tumors are more likely to be aggressive.
All breeds of horses are susceptible to melanomas, but their incidence is probably over-represented in Percherons, Arabians, and Andalusians, all breeds in which the color gray is very common.
Melanomas in dogs and humans have a complex system of classification, but equine melanomas usually are characterized as benign or malignant. They can develop in one of three distinct ways:
a) The melanomas develop slowly, over a number of years, without metastasis, and can remain benign for 10 to 20 years (this is the most common scenario).
b) Benign melanomas that have existed for months or years suddenly assume malignant characteristics and begin to spread rapidly externally and/or internally.
c) Melanomas are malignant from their first appearance and readily metastasize. In rare cases, they might even be congenital (present at birth). Fortunately, this is the least common possibility.
Melanoma Management
As with sarcoids, sometimes melanomas require no treatment at all, if they’re slow-growing and not interfering with any of the horse’s daily functions. Many gray horses exist happily enough for years with benign melanomas that cause them little or no discomfort.
However, just because a tumor appears to be inactive doesn’t mean you should stop monitoring it. There always is the possibility that something will trigger a change to malignancy, so it’s important to examine tumors regularly for changes in size, number, or appearance.
“If you’re the owner of a gray horse,” says Carr, “the best thing you can do is closely monitor him, from the age of about six on up. Melanomas will develop eventually. When they do, talk to your veterinarian early on and discuss treatment—don’t leave it till they get very large.”
Treatments For Melanomas
A bewildering array of treatment options exists for melanomas, and again, as with sarcoids, no one method has emerged as having a uniformly rewarding success rate. Your veterinarian might want to try one or more of the following:
Surgical Excision—The simplest approach for slow-growing, small to moderate-sized tumors (less than three centimeters in diameter) in surgically accessible locations. Large “sheets” of melanoma tissue are not good candidates for surgery, as it would prove very invasive and the chances are slim that you’d be able to remove 100% of the tumor. Even with solitary tumors, rapid recurrence often is a problem, as it’s difficult to tell whether you’ve been able to remove all the abnormal cells. Surgical excision might be used to “de-bulk” a large tumor mass in order to improve the chances of success of other treatment methods, such as one of the following:
Cryonecrosis—As with sarcoids, freezing with liquid nitrogen might help kill the remaining cells in the tumor “bed” after the majority of a large melanoma has been removed by surgery or with surgical lasers. The surface tissue is frozen to -20° Celsius, allowed to thaw, then frozen a second time. This procedure usually can be done with the horse standing and sedated. Combining surgical removal with “cryo” treatment rarely cures melanomas, but it very often can keep the tumors of a manageable size when the freezing is repeated once or twice a year.
Chemotherapy—Cispla-tin, the chemotherapy drug, also has been found to be useful for single, small-to-moderate-sized melanomas, injected intra-lesionally (into the tumor itself) every two weeks for a total of four treatments. (Systemic chemotherapy—in which the drug is injected into the muscle or a vein rather than into the tumor itself—has proven to have little or no effect on equine melanomas.) The results vary depending on how successfully the drug diffuses through the tissues (the injection technique usually involves using a fine-gauge needle and many applications of the drug, five to eight millimeters apart). Encouragingly, though, cisplatin has been used on pregnant broodmares and breeding stallions with no signs of toxicity. Tumors do tend to recur a few months after cisplatin treatment ceases, but horses develop no resistance to the drug, so the treatment can be repeated if necessary.
Radiation—Radiation therapy, similar to that used on sarcoid tumors, also is a possibility if you are lucky enough to have an appropriately equipped veterinary hospital nearby. Says Carr, “We’ve been using radiation therapy on some melanomas in awkward locations with pretty good success.”
Latest Therapy: Cimetidine
One of the most promising advances in the treatment of melanoma is the drug cimetidine (trade name Tagamet). Borrowed from human medicine, where it has been shown to treat malignant melanomas and some other types of tumors, cimetidine has been used with good success in horses since 1985. The drug often is able to reduce the size and number of a horse’s tumors, although veterinarians caution there is no way to tell whether an individual horse will respond to the treatment until it is tried. It’s estimated that 30%-50% of horses treated do respond to some degree. A good response is a 50% reduction in the size and/or number of melanomas, and no further progression of the disease for several years. (In a few cases, cimetidine has even been documented to cause tumors to regress completely, apparently curing the horse.)
Researchers aren’t completely sure how cimetidine works on melanomas, but they do know that in an active melanoma, T suppressor cells are present to dampen the immune response to the abnormal cells. Cimetidine appears to block the activation of these T suppressor cells, thus helping stimulate the body’s anti-tumor defense system. Not surprisingly, cimetidine works best on tumors that are actively growing. Results with tumors that aren’t changing in size or appearance generally have been disappointing.
Although cimetidine is a ray of hope for many owners, it’s an expensive and inconvenient drug, best administered orally at a level of 2.5 milograms/kilograms of body weight, at eight hour intervals, over a course of weeks or months. Giving the drug only once or twice a day doesn’t appear to give nearly the same results. If your horse is going to respond to cimetidine, you’ll start to see a change in the size and/or number of the tumors within two to seven weeks. If that occurs, your veterinarian will continue the therapy until he/she sees no further change for a period of two to three weeks. If your horse’s tumors show no changes after three months of treatment, the therapy should be discontinued, as it will be evident by then that you’ll get no response.
Could be a melanoma, common for greys, especially arab types.
(didnt the vet take any tests etc)anyway:
Miserable Melanomas
Every owner of a gray horse lives in fear of melanomas, those characteristic black or brown nodules that so often appear on the skin around and under the tail. Rightly so, for estimates suggest that more than 80% of gray horses over the age of 15 will develop at least one melanoma tumor during its lifetime. The “why” hasn’t been determined. We know that melanomas are tumors of the melanocytes, the cells that produce skin pigment. We know that in aging gray horses there appears to be a disturbance in the metabolism of melanin, which stimulates local over-production of dermal pigment. But why gray horses are particularly susceptible isn’t yet clear. (One thing is reasonably certain—unlike melanomas in humans, which might be triggered by overexposure to ultraviolet radiation, gray-horse melanomas don’t appear to be linked to an overdose of sun. The shady locations in which they tend to develop, and the fact that the skin of gray horses is black, and thus well-protected from U/V radiation, attest to this.)
Melanomas can be hard or soft, solitary or appearing in clusters. Often, they’re subcutaneous when they first appear, covered by normal skin, but as they develop over time, they become more obvious, and their surfaces can become ulcerated and/or infected. Although they’re generally dark brown, gray, or black in color, it’s also possible for these tumors to be unpigmented (amelanotic), a situation which makes diagnosis considerably more challenging (microscopic examination of biopsy samples being the only way to identify these “invisible” tumors).
The underside of the tail, the perineal and peri-anal regions, and the penis and sheath in males are the most common locations for melanomas to sprout. They also can be found on the ear margins, elsewhere on the head, in the jugular region, and near or on the parotid salivary gland. It’s quite possible for melanomas to spread internally as well, most commonly gravitating to the serosal surfaces of the liver, spleen, and lungs.
Much of the time, melanomas are fairly benign, slow-growing tumors, and are more unsightly than dangerous. They might remain that way for years or even decades. Within each tumor, however, lurks the potential for an overnight change to malignant growth, which swiftly can change the situation from a cosmetic nuisance into something life-threatening.
They might appear as rapidly spreading series of lumps or nodules, or even as vast, rippling sheets of black tumor masses across the tissue. Malignant melanomas can interfere with a horse’s excretory functions, with breeding and foaling, or, if found in other locations on the body, such as the back or neck, with working under saddle or in harness.
Because malignant melanomas frequently appear in multiple sites, and because they have a high rate of metastasis, they can be very difficult to cure. Gray horses aren’t the only ones affected; horses of other coat colors also can develop melanomas. The incidence in non-grays is much lower, but when melanomas do appear in these horses, the tumors are more likely to be aggressive.
All breeds of horses are susceptible to melanomas, but their incidence is probably over-represented in Percherons, Arabians, and Andalusians, all breeds in which the color gray is very common.
Melanomas in dogs and humans have a complex system of classification, but equine melanomas usually are characterized as benign or malignant. They can develop in one of three distinct ways:
a) The melanomas develop slowly, over a number of years, without metastasis, and can remain benign for 10 to 20 years (this is the most common scenario).
b) Benign melanomas that have existed for months or years suddenly assume malignant characteristics and begin to spread rapidly externally and/or internally.
c) Melanomas are malignant from their first appearance and readily metastasize. In rare cases, they might even be congenital (present at birth). Fortunately, this is the least common possibility.
Melanoma Management
As with sarcoids, sometimes melanomas require no treatment at all, if they’re slow-growing and not interfering with any of the horse’s daily functions. Many gray horses exist happily enough for years with benign melanomas that cause them little or no discomfort.
However, just because a tumor appears to be inactive doesn’t mean you should stop monitoring it. There always is the possibility that something will trigger a change to malignancy, so it’s important to examine tumors regularly for changes in size, number, or appearance.
“If you’re the owner of a gray horse,” says Carr, “the best thing you can do is closely monitor him, from the age of about six on up. Melanomas will develop eventually. When they do, talk to your veterinarian early on and discuss treatment—don’t leave it till they get very large.”
Treatments For Melanomas
A bewildering array of treatment options exists for melanomas, and again, as with sarcoids, no one method has emerged as having a uniformly rewarding success rate. Your veterinarian might want to try one or more of the following:
Surgical Excision—The simplest approach for slow-growing, small to moderate-sized tumors (less than three centimeters in diameter) in surgically accessible locations. Large “sheets” of melanoma tissue are not good candidates for surgery, as it would prove very invasive and the chances are slim that you’d be able to remove 100% of the tumor. Even with solitary tumors, rapid recurrence often is a problem, as it’s difficult to tell whether you’ve been able to remove all the abnormal cells. Surgical excision might be used to “de-bulk” a large tumor mass in order to improve the chances of success of other treatment methods, such as one of the following:
Cryonecrosis—As with sarcoids, freezing with liquid nitrogen might help kill the remaining cells in the tumor “bed” after the majority of a large melanoma has been removed by surgery or with surgical lasers. The surface tissue is frozen to -20° Celsius, allowed to thaw, then frozen a second time. This procedure usually can be done with the horse standing and sedated. Combining surgical removal with “cryo” treatment rarely cures melanomas, but it very often can keep the tumors of a manageable size when the freezing is repeated once or twice a year.
Chemotherapy—Cispla-tin, the chemotherapy drug, also has been found to be useful for single, small-to-moderate-sized melanomas, injected intra-lesionally (into the tumor itself) every two weeks for a total of four treatments. (Systemic chemotherapy—in which the drug is injected into the muscle or a vein rather than into the tumor itself—has proven to have little or no effect on equine melanomas.) The results vary depending on how successfully the drug diffuses through the tissues (the injection technique usually involves using a fine-gauge needle and many applications of the drug, five to eight millimeters apart). Encouragingly, though, cisplatin has been used on pregnant broodmares and breeding stallions with no signs of toxicity. Tumors do tend to recur a few months after cisplatin treatment ceases, but horses develop no resistance to the drug, so the treatment can be repeated if necessary.
Radiation—Radiation therapy, similar to that used on sarcoid tumors, also is a possibility if you are lucky enough to have an appropriately equipped veterinary hospital nearby. Says Carr, “We’ve been using radiation therapy on some melanomas in awkward locations with pretty good success.”
Latest Therapy: Cimetidine
One of the most promising advances in the treatment of melanoma is the drug cimetidine (trade name Tagamet). Borrowed from human medicine, where it has been shown to treat malignant melanomas and some other types of tumors, cimetidine has been used with good success in horses since 1985. The drug often is able to reduce the size and number of a horse’s tumors, although veterinarians caution there is no way to tell whether an individual horse will respond to the treatment until it is tried. It’s estimated that 30%-50% of horses treated do respond to some degree. A good response is a 50% reduction in the size and/or number of melanomas, and no further progression of the disease for several years. (In a few cases, cimetidine has even been documented to cause tumors to regress completely, apparently curing the horse.)
Researchers aren’t completely sure how cimetidine works on melanomas, but they do know that in an active melanoma, T suppressor cells are present to dampen the immune response to the abnormal cells. Cimetidine appears to block the activation of these T suppressor cells, thus helping stimulate the body’s anti-tumor defense system. Not surprisingly, cimetidine works best on tumors that are actively growing. Results with tumors that aren’t changing in size or appearance generally have been disappointing.
Although cimetidine is a ray of hope for many owners, it’s an expensive and inconvenient drug, best administered orally at a level of 2.5 milograms/kilograms of body weight, at eight hour intervals, over a course of weeks or months. Giving the drug only once or twice a day doesn’t appear to give nearly the same results. If your horse is going to respond to cimetidine, you’ll start to see a change in the size and/or number of the tumors within two to seven weeks. If that occurs, your veterinarian will continue the therapy until he/she sees no further change for a period of two to three weeks. If your horse’s tumors show no changes after three months of treatment, the therapy should be discontinued, as it will be evident by then that you’ll get no response.