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Is That a Skin Tumor?


© Text Copyright 2008, Tufts University. All rights reserved. Reprinted with permission from Your Dog,May 2008.

No portion of this article may be reproduced without permission of the copyright holder. Reprinted with permission from Text Copyright , Tufts University. All rights reserved. Reprinted with permission from Your Dog,May ..

Any lumps and bumps on your dog's skin — whether large or small— warrant prompt veterinary diagnosis. Here's why.

There's no need to panic if you happen to spot a strange lump, bump or scabby sore on your dog's skin. But it would be wise to have the animal examined by your veterinarian.

It's quite possible that an unsightly growth will be nothing more than a harmless wart or cyst. On the other hand, you might discover a skin tumor in an early stage of development — a potentially worrisome situation, depending on the type of tumor. It might be an excessive but harmless proliferation of fat or other tissue. Or it could be an early sign of a lethal skin cancer. An estimated 25 percent of all dogs will develop cancer at some point in their lives — and skin is by far the most commonly affected organ.

The most important thing an owner can do is to have a veterinarian examine any lump or bump as soon as it becomes apparent.Benign Growths

Skin growths that are unlikely to pose a serious or long-term health threat are referred to as benign. Although some of these growths can become alarmingly large, they are typically small, well defined and inconsequential. Their cells do not normally spread to adjacent tissue and involve other organs in the way that potentially deadly malignant tumors do.

Common canine skin growths include cysts (skin-covered, pea-sized sacs filled with a liquid or a thick, cheesy substance) and warts(hard, rough-surfaced lumps that are often  by viral infections). Such growths occur frequently in the life of a typical dog. Some animals may have several of them at the same time, but unless they become ulcerated or seriously annoy an animal, they typically don't require treatment.

Among the most frequently diagnosed benign tumors in dogs are accumulations of soft, fatty tissue that develop just beneath the skin surface. According to Margaret McEntee, DVM, an associate professor of oncology at Cornell University's College of Veterinary Medicine, these growths (called lipomas) are usually small — perhaps the diameter of a large coin — but they can become "quite sizable." In fact, she says, "The largest lipoma that I've seen was nearly the size of a basketball."

In most cases, notes Dr. McEntee, a lipoma will be harmless, and it will not have to be removed. In some instances, however, a large mass of the fatty tissue will develop in a dog's axillary area — at the top of a fore-limb — and will inhibit the animal's ability to walk or run, in which case its surgical removal will be advisable. Also, she points out, a grossly enlarged lipoma is apt to be unsightly and may be removed for cosmetic reasons. If surgery is performed, she says, removal of the mass is usually easy to accomplish. "We don't know why lipomas develop," says Dr. McEntee. "Thin dogs get them as frequently as overweight dogs. It's possible that there is some hereditary component. Certain breeds — Labrador retrievers, for example — seem to develop them more often than other breeds."

Adenomas, another type of benign skin tumor, develop in an animal's sebaceous glands, which are mostly associated with hair follicles. "They are usually quite small," says Dr. McEntee. "Animals tend to have quite a few of these skin growths on various areas of their bodies. Adenomas seem to be especially prevalent in certain breeds such as miniature poodles and cocker spaniels." While adenomas are usually benign, she notes, cancerous growths called adenocarcinomas sometimes develop in the same glands. And a malignant glandular tumor called a perianal adenocarcinoma can develop in the tissues around a dog's anus.

Malignant Growths

Unlike benign tumors such as lipomas and most adenomas, malignant skin tumors —lesions that have the potential to grow uncontrollably, to travel (metastasize) and to invade other tissues and organs in a dog's body — must be treated without delay whenever possible. According to Dr. McEntee, the most frequently diagnosed skin malignancy by far is a mast cell tumor. These growths, she says, account for about 20 percent of all canine skin tumors, including the various benign growths.

Mast cells are essentially white blood cells, important immune cells whose ingredients include histamine (a chemical that is released by the immune system as part of an allergic reaction) and heparin (an anticoagulant substance). Mast cells are found in a dog's skin and other tissues, such as cartilage and bone. Although mast cell tumors appear most often in golden retrievers and Labrador retrievers, the condition is by no means associated only with those breeds. Boxers, for example, are also at elevated risk, as are a number of other canine breeds.

Another type of canine skin malignancy — less common than mast cell tumors but of serious concern — is squamous cell carcinoma, which affects the flat, scaly cells on the outer layer of the skin. Dogs that have lightly pigmented skin — especially white dogs —are especially predisposed, regardless of breed. Direct and prolonged exposure to solar radiation is a significant contributing factor for squamous cell cancer; thus, a dog that habitually lies on its back basking in bright sunlight is at especially high risk.

Other relatively common types of canine skin cancers include melanomas, which form in pigmented skin cells; fibrosarcomas, which form in fibrous tissue; and hemangiopericytomas, which form near blood vessels.

An owner can reduce the risk of canine squamous cell cancer by limiting an animal's exposure to direct sunlight, especially if it is lightly pigmented or pure white. Otherwise, there is no known way to prevent the occurrence of either benign or malignant skin tumors. "The most important thing for owners to do," advises Dr. McEntee, "is to have a veterinarian look at any new lump or bump as soon as it becomes apparent. In some cases, the veterinarian will recommend that you just keep an eye on the lesion and see if it changes in appearance. In other cases, a biopsy or other diagnostic measures will be recommended. And, of course, in still other cases, the veterinarian may recommend surgery or another type of treatment."

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