Causes of Skin Tumors in Dogs
Skin tumors are among the most common tumors in dogs. Fortunately, most of them are benign. Skin tumors can be caused by many different things, including infection (bacterial, viral or fungal), cancer (neoplasia) or the simple accumulation and compaction of fat. Skin masses may be pimples, pustules, hives, hematomas, cysts, blisters, abscesses, lick granulomas or skin tags. Some of the most common cutaneous (within the skin) and subcutaneous (underneath the skin) masses that affect domestic dogs are listed below. This is a very general overview. Only a veterinarian can accurately diagnose what any particular lump is, and how it should be treated.
- Abscess – A skin abscess is a localized collection of pus, usually found at the site of a puncture or bite wound, formed by the disintegration of tissue. Most abscesses are caused by a bacterial infection, but occasionally they are caused by fungi or other microorganisms. Abscesses usually are quite painful.
- Anal Sac Apocrine Gland Tumor – Apocrine adenocarcinomas are the most common canine anal sac tumor. They are most common in older females.
- Basal Cell Tumor – Most basal cell tumors are single, round, hairless nodules located on a narrow stem or stalk. Like many other masses, basal cell tumors can ulcerate. They typically are found on the head, neck and shoulders of older dogs.
- Dermoid Cysts – Dermoid cysts are small, benign cysts typically seen in young dogs. They arise from the dermis (inner) layer of the skin and usually are covered with hair. They are most common in Boxers and Rhodesian Ridgebacks. Fortunately, they don’t pose a health risk to dogs.
- Hemangioma/Hemangiosarcoma – Hemangiomas are benign tumors made up of newly formed blood vessels clustered tightly together. They commonly occur on the skin and in the spleen of dogs. Hemangiosarcomas are malignant masses that usually metastasize or spread to distant locations and bleed profusely if cut or disturbed. Some reports suggest that German Shepherd Dogs have an increased risk of developing hemangioma and hemangiosarcoma.
- Hematoma – A hematoma is a localized collection of blood, usually clotted, that can occur anywhere in the body. Hematomas are often found along the edges of a dog’s ear flaps.
- Histiocytoma – Cutaneous histiocytomas are fast-growing, dome-shaped growths most commonly seen in young adult dogs. Histicytomas can be found anywhere on a dog’s body. Flat-Coated Retrievers seem particularly predisposed to developing this type of tumor. Other breeds that may be at increased risk include the American Staffordshire Terrier, Boston Terrier, Boxer, Cocker Spaniel, Dachshund, Doberman Pinscher, English Springer Spaniel, Great Dane, Miniature Schnauzer, Labrador Retriever, Rottweiler, Scottish Terrier, Shetland Sheepdog, Shar-Pei and West Highland White Terrier.
- Lipoma – Lipomas are benign tumors of fatty tissue. They are grouped with skin tumors because they often are quite superficial, located just beneath the skin. Lipomas are extremely common in dogs, especially as they age. Middle-aged and older Doberman Pinschers, Cocker Spaniels, Dachshunds, Labrador Retrievers, Weimaraners and Miniature Schnauzers are particularly affected by lipomas. It is important to differentiate lipomas from more serious skin masses. Lipomas are normally well-circumscribed, smooth and fairly movable. They can range in size from a small grape to a cantaloupe. Lipomas are most commonly found along a dog’s rib cage or in the chest area. They occasionally develop stalk-like projections that connect them to nearby tissues; these are called “pedunculated lipomas.” Most lipomas don’t require medical treatment, unless they are near a joint and interfere with a dog’s movement. Some owners opt to have lipomas removed surgically for cosmetic reasons.
- Lymphoma – Lymphoma is one of the most common cancers in domestic dogs. While lymphoma is typically characterized by tumors of tissue in the lymph nodes, liver, spleen and/or bone marrow, there is a skin form that causes raised, round nodules.
- Mast Cell Tumor – Mast cell tumors are the most common skin tumors in domestic dogs. They can develop on the skin (cutaneous) or in underlying tissue (subcutaneous). Mast cell tumors take a variety of forms: they can be bumpy or smooth, poorly or well circumscribed, soft or firm, hairless or ulcerated, red or dark, and solitary or in multiple places. Most commonly, mast cell tumors appear on a dog’s trunk, around its anus or on its legs. These are malignant masses that are highly invasive and difficult to treat with complete success. They appear most commonly in older dogs and in Boxers, American Staffordshire Terriers, Pugs, Boston Terriers, Labrador Retrievers, Weimaraners, Beagles, Dachshunds, Chinese Shar Peis, English Bulldogs, Bull Terriers, Fox Terriers and Golden Retrievers.
- Melanoma – Melanomas are brown or black pigmented nodules that usually show up on dark areas of a dog’s skin or in its mouth or eyes. Many canine melanomas are malignant.
- Papilloma – Papillomas, also known as “warts,” are benign tumors that arise from skin, mucous membranes and/or ducts associated with glandular tissue. They are small, discrete round growths with a rather rough surface. They often are pedunculated, which means that they have a stem-like stalk connecting them to normal tissue. Papillomas can show up in large numbers, but fortunately they usually are not dangerous or painful. Papillomas are caused by viruses and tend to be seen in young dogs and immunocompromised adults. Papillomas are more common in Poodles, Cocker Spaniels, Kerry Blue Terriers, Miniature Schnauzers and Pugs. The lesions often appear on the eyelids, in the genital region, on the back or on the lips, gums, tongue, palate or muzzle. Viral papillomas are transmissible between dogs, but not from dogs to people or cats. Uncommonly, papillomas may metastasize to squamous cell carcinoma. They also can ulcerate and bleed, causing discomfort.
- Perianal Adenoma – Perianal adenomas are masses that develop from the glands surrounding the anus. They look like small clusters of grapes, and they often bleed. Perianal tumors can be extremely irritating to affected dogs. Older, intact males are predisposed to developing these masses. Castration of young males usually prevents perianal adenomas from forming. They can also be surgically removed, although regrowth is common.
- Sebaceous Gland Tumor – Sebaceous gland tumors are small benign masses that can be solitary or appear in a group and usually are raised, firm, wart-like or cauliflower-like, ranging from a few millimeters to several centimeters in diameter. They can be pink, yellowish or darkly pigmented and may be oily, ulcerated or alopecic (hairless). In dogs, they are especially common on the belly (ventral abdomen), but they can show up anywhere. They also are often seen on and around the eyelids and legs of older dogs. There are several different types of canine sebaceous gland tumors, including nodular sebaceous hyperplasia, sebaceous epitheliomas and sebaceous adenomas. These are most commonly seen in older dogs – especially Beagles, Poodles, Dachshunds, Cocker Spaniels, Miniature Schnauzers, Lhasa Apsos, Shih Tzus, Malamutes, Siberian Huskies and Irish Setters.
- Sebaceous Cysts – Sebaceous cysts are one of the most common skin cysts found in companion dogs. A “cyst” is a closed sac-like space that contains a liquid or semi-solid substance of some sort. Most cysts are harmless. However, they occasionally develop into malignant growths, and they can also become infected. Dogs have a number of sebaceous glands along the top of their necks and on their backs. These glands produce oils, called “sebum”, which lubricate the hair coat and skin. If the tiny pores that open the sebaceous glands to the skin become plugged, a cyst can form, because the glands will continue to produce sebum. Sebaceous cysts are not particularly dangerous. However, than can become extremely large and painful. Surgical removal is the treatment of choice.
- Soft-Tissue Sarcoma – Soft tissue sarcomas can vary greatly in size, shape and appearance. These tumors may grow rapidly, but they typically are slow-growing masses.
Squamous Cell Carcinoma – Squamous cell carcinoma is a malignant type of skin cancer which can cause serious health problems in affected dogs. These tumors are typically rough, reddish or grey and bumpy like a cauliflower. They can ulcerate and become open, oozing, bleeding wounds. Squamous cell carcinomas are most commonly found on a dog’s belly, scrotum, legs, feet, lips and/or muzzle. Long-term exposure to sunlight increases the risk of this type of cancer. Squamous cell tumors should be surgically removed if possible; chemotherapy and/or radiation may also be appropriate.
- Transmissible Venereal Tumor – These masses occur on the genitalia of both male and female dogs. They frequently are weeping, ulcerated and rough on the surface. As their name indicates, these tumors are contagious between dogs.
This is a generalized and partial list of the types of lumps and bumps that can occur on or just under a dog’s skin. Your veterinarian is the best person to help you diagnose and, if necessary, treat any skin tumors.
There is no reliable way to prevent most skin tumors. Dogs that have a primarily white coat are prone to developing malignant melanoma more commonly than other dogs and probably should not be exposed to sunlight for prolonged periods of time.
Skin tumors are common in domestic dogs. They may be nothing more than a cosmetic bother, but sometimes they reflect a much more serious medical condition. When you groom or pet your dog, always be alert for any suspicious lumps or bumps, with or without accompanying or persistent sores. Either way, dogs with skin tumors should be seen by a veterinarian.