Skin Tumors in Animals


Tumors are abnormal growths of cells. Skin tumors are diagnosed more frequently than other tumors in animals because the skin is constantly exposed to many tumor-causing factors in the environment. Chemicals, solar radiation, and viruses, Hormonal abnormalities and genetic factors may also play a role in the development of skin tumors.
All of the various layers and components of skin have the potential for developing distinctive tumors. Distinguishing a tumor from an inflammatory disease can sometimes be difficult. Tumors are usually small lumps or bumps, but they also can occur as hairless, discolored patches, rashes, or non-healing ulcers.

Tumors may be benign or malignant (cancerous). Malignant tumors can spread and cause harm to the animal. Distinguishing a benign tumor from a cancerous tumor requires specialized knowledge and laboratory equipment. A veterinarian can perform a fine needle aspiration of cells or a biopsy (which removes a small amount of tissue from a tumor) for evaluation.
Treatment for a particular tumor depends largely on the type of tumor, its location and size, and the overall physical condition of the dog. For benign tumors that are not ulcerated and do not impair the dog's normal routine, treatment may not be necessary. This may be the most prudent option, especially in aged animals.
There are several treatment options for cancerous tumors and benign tumors that inhibit normal activities or are cosmetically unpleasant. For most tumors, surgical removal is the most effective option. It is also probably the least costly option and the one with the fewest side effects. If malignancy is suspected, tissue surrounding the tumor will also be removed to increase the chance that none of the tumor cells are left behind. For tumors that cannot be completely removed, partial removal may prolong the life of the dog. Radiation treatment or chemotherapy may also be used to provide your pet with a better outcome.
In addition to skin and hair follicle tumors, there are also tumors that affect the ceruminous glands.
(Ceruminous glands are specialized sudoriferous glands (sweat glands) located subcutaneously in the external auditory canal)

Apocrine Gland Tumors of the Anal Sac
These tumors most commonly appear as deep, firm, masses near the anal sacs. As the tumors grow, they may compress the rectum and induce constipation. Chemotherapy and radiation treatment may also be provided. Few animals live more than a year after this type of tumor has been diagnosed.
Basal Cell Tumors and Carcinomas
Basal cells lie at the base of the top layer of the skin (the epidermis). A benign growth of these cells is a basal cell tumor. A malignant growth is a basal cell carcinoma.
Benign, Nonviral, Wart-like Tumors
These tumors are not, in the strictest sense, warts though they may look a lot like warts. These tumors are often easy to remove and there is little threat to the overall health of the animal.
Blood Vessel Tumors
Blood vessel (vascular) tumors of the skin and soft tissues are growths that closely resemble blood vessels. Some forms are benign while others are highly malignant.
Histiocytic Cell Tumors
These tumors form a group of poorly defined skin diseases all characterized by a proliferation of cells called histiocytes (tissue macrophages). The cause for these diseases is unknown..
Keratinized Skin Cysts
Some animals develop cysts that are filled with keratin, a skin protein. Such cysts have a hard or solid core. Most are malformations of hair follicles and may be the same color as the hair. There are several kinds of keratinized skin cysts. The ones found in animals include isthmus catagen cysts, matrix cysts, hybrid cysts (panfollicular cysts), and dermoid cysts.Dermoid cysts are congenital (the animal is born with them). Surgical removal is the best treatment. Do not attempt to remove the cysts by squeezing them because this can spread the cyst contents into the surrounding tissues..
Lipomas and Liposarcomas
Lipomas are benign tumors of fat (adipose tissue) and are common in animals. Lipomas generally occur in older, obese females, most commonly on the trunk and near the tops of the legs.
Lipomas are one of the most common benign tumors of the skin in dogs.
Liposarcomas are rare tumors in all domestic animals. Most are recognized in older male animals in which they usually develop on the chest and legs. Wide surgical removal (removing both tumor and some surrounding tissue) is most often recommended. Recurrence is common, so follow up radiation treatment may be required.
Mast Cell Tumors
Mast cell tumors are named for the type of cell from which they grow. Mast cells are involved in allergic reactions. They release histamine, which causes irritation and itching, and other chemicals that may cause shock. Mast cell tumors may be seen in animals of any age but occur most commonly in animals 8 to 10 years old. They may develop anywhere on the body surface as well as in internal organs, but the limbs (especially the back of the upper thigh), lower abdomen, and chest are the most common sites. Tumors located near mucous membranes or on the lower surface of the body are more likely to spread than mast cell tumors in other areas.
These tumors vary greatly in size and rate of growth. Animals can also develop signs associated with the release of toxins from the malignant mast cells. For example, up to a quarter of animals with mast cell tumors also have stomach ulcers due to histamine release. Diagnosis is by microscopic examination of fine needle aspirations, impression smears, or biopsy samples.
A melanoma is a dark-pigmented skin tumor that may be either benign (not cancerous) or malignant (cancerous). Benign melanomas are diagnosed much more frequently in animals than malignant melanomas. They most commonly develop on the head and forelimbs in middle-aged or older animals.
Malignant melanomas most commonly develop in older animals. The lips, mouth, and nail beds are the most common sites of development. Malignant melanomas on haired skin are rare, and most arise on the lower abdomen and the scrotum. Males are affected more often than females.
Treatment consists of complete surgical removal. However, the spreading nature of the tumor may make this difficult. When present on a toe, amputation of the involved toe is the standard treatment. When present on the mouth, surgical removal of part of the jaw may allow for complete tumor removal and an acceptable postsurgical cosmetic appearance and survival. Melanomas are generally considered resistant to radiation treatment, and there is no established chemotherapy known to be highly effective. Typical survival times for animals with malignant melanomas range from 1 to 36 months. A vaccine that helps shrink the size of malignant melanomas in animals and prolong survival was conditionally licensed by the US Department of Agriculture in 2007.
Perianal (Hepatoid) Gland Tumors
Perianal gland tumors are a type of tumor found near the anus in animals. They occur mostly in a specialized gland found in the anal sac. The tumors appear as one or (more commonly) multiple lumps 0.2 to 4 inches (0.5 to 10 centimeters) in diameter. Larger tumors commonly form ulcers and bleed. In addition, large tumors can compress the anal canal and make defecation difficult.
Up to 95% of male animals with these tumors are cured by castration. Surgical removal of the tumors may be used to remove extremely large or ulcerated tumors that have become secondarily infected. Surgery is the treatment of choice for females but may need to be repeated because recurrence is common in females. Radiation treatment is also an option and may be prescribed either alone or in combination with surgery. Laser surgery and cryosurgery (freezing) are other options, but because fecal incontinence is very common following extensive surgery involving the sphincter, this option is used only when tumors cannot be removed using regular surgical techniques..
Sebaceous Gland Tumors
The sebaceous glands secrete the oil known as sebum into the hair follicles and onto the skin. Tumors of sebaceous glands are common in dogs.
Sebaceous gland adenocarcinomas are a rare malignant form of sebaceous gland tumor. They occur in middle-aged or older animals.. They spread within the skin and may spread to regional lymph nodes late in the disease.
For malignant adenocarcinomas, surgery is the treatment of choice. Your veterinarian will remove not only the tumor but also tissue around the tumor, including involved lymph nodes. In addition, chemotherapy and radiation treatment may also be prescribed. Animals that develop a sebaceous gland overgrowth or adenoma often develop new tumors at other sites.
Squamous Cell Carcinomas
Squamous cell carcinomas are malignant tumors. They can be found in all domestic animals. In animals, these are the most frequently diagnosed carcinomas of the skin. Two forms occur in animals—skin and subungual. Skin squamous cell carcinomas are tumors of older dogs. Bloodhounds, Basset Hounds, and Standard Poodles are at greatest risk. They appear on the head, lower legs, abdomen, and rear. Most appear as firm, raised, frequently ulcerated patches and lumps. Sometimes they can grow outward with a surface like a wart. Some are caused by prolonged sun exposure. These usually develop on the lower abdomen, especially on or near the pubic area in white-skinned, shorthaired breeds such as Dalmatians, Bull Terriers, and Beagles. They develop on the underside of animals because the poorly haired skin offers minimal shielding from ultraviolet radiation. Many animals sun themselves lying on their backs. They also get some solar radiation that reflects from the ground. Before a malignant tumor develops, animals develop solar keratosis. Solar keratosis is thickened and discolored skin. Thus, finding areas on your dog where the skin is thick and discolored is cause for a veterinary checkup. Early diagnosis is important for successful treatment.
Sweat Gland Tumors
There are 2 types of sweat glands in animals, called apocrine and eccrine. Apocrine gland cysts are found in middle-aged or older animals. They can occur either in or outside of hair follicles. They appear most commonly on the head and neck. One or more cysts develop in the middle to upper skin layer with a loose association with hair follicles. Another form is more diffuse and involves cysts within the glands associated with multiple hair follicles in uninjured skin. Both forms of apocrine gland cysts are benign (not cancerous). Treatment is by surgical removal, though this may be difficult if the cysts are diffused.
Tumors Originating Outside the Skin (Metastatic Tumors)
All malignant tumors, wherever they originate, are capable of spreading to the skin. However, the spread of a primary tumor from inside the body to the skin is unusual. Although the appearance is variable, the tumors that spread to the skin are usually multiple, ulcerated lumps. As these tumors grow, they extend deeper into the skin and surrounding tissue. Generally, it is difficult to identify the primary tumor based on the signs in the skin. This is because only a small population of cells in the primary tumor will spread to the skin, and these cells may have different microscopic features than the primary tumor. When tumors have spread from other areas of the body to the skin, the primary tumor usually grows and spreads quickly and the outlook for a positive outcome is guarded. Treatment for these tumors involves a whole-body approach that deal with both the skin tumors and the primary tumor(s).
Warts (Papillomas)
Warts are caused by papillomaviruses. The virus is transmitted by direct contact or by contact with contaminated items such as bedding, clothing, dishes, and other items . It is also possible that insects may spread papillomaviruses. There are several distinct papillomaviruses. Warts have been reported in all domestic animals and are most common in animals and horses.
Multiple warts of skin or mucus membranes generally are seen in younger animals. Single warts are more frequent in older animals, but they may not always be caused by viral infection. The period between the initial infection and the development of visible warts varies but normally takes several months.
Most warts appear as bumps with a hardened surface resembling a cauliflower. When multiple warts are present they may be sufficiently characteristic to make a working diagnosis. However, there are many things that look like warts and a definitive diagnosis may require identification of the virus or its effects on individual cells (a change known as koilocyticatypia or koilocytosis).

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