Dog Skin Tumors

Introduction

Most owners will find unexplained lumps and bumps on their dog at some point in time. Many different types of masses can appear either on (cutaneous), or just under (subcutaneous), a dog's skin. It is important for dog owners to have these lumps checked by a veterinarian, especially if the masses are new, bleeding, oozing and/or rapidly growing. Many skin masses are harmless, but others can be malignant or become malignant and need to be taken seriously.

Causes & Prevention

Causes of Skin Tumors
Canine skin masses can be caused by a number of things, such as infection (bacterial, viral, fungal), cancer (neoplasia) or simple accumulation of fat. Other forms of skin lumps include pimples, pustules, hives, hematomas, cysts, blisters (vesicles), abscesses, lick granulomas and skin tags. Some other recognized cutaneous and subcutaneous masses that can affect domestic dogs are listed below. Please remember, this is a cursory overview that is extremely generalized. Only a veterinarian can diagnose exactly what any particular lump or bump is, and what its consequences to the dog and the owner may be.

Lipoma - Superficial uncomplicated fatty tumors called lipomas are common in dogs, especially as they grow older. These masses tend to be smooth and fairly soft beneath the skin; they almost feel like a large grape that is loose under the skin but close to its surface. Most lipomas do not require medical treatment. However, some owners opt to have them removed surgically for cosmetic reasons. Sometimes, lipomas develop stalk-like projections or extentions that connect them to nearby tissues. These are called pedunculated lipomas. While they do not usually cause particular problems in dogs, they can be quite dangerous to horses as a cause of strangulating intestinal colic.
Papilloma – Papillomas are benign tumors that can arise from skin, mucous membranes, conjunctiva of the eyes and ducts associated with glands. They usually are not dangerous or painful. This is the common "wart". Squamous cell carcinoma – These tumors are often rough, reddish or grey and resemble a cauliflower. They can be ulcerated, which basically means they look like an open, oozing or bleeding wound, and they seem to be most common on the underside of affected dogs – on the belly, scrotum, legs, feet and/or muzzle.
Basal cell tumor – Most basal cell tumors are single, hairless nodules on a narrow stem or stalk. Sometimes they are ulcerated.
Sebaceous gland tumor/adenoma – Sebaceous adenomas are usually fairly small (often less than one inch in diameter). They tend to be smooth, pink and common on and around the eyelids and legs of older dogs. Anal sac apocrine gland tumor – Apocrine adenocarcinomas are the most common canine anal sac tumor and are seen most commonly in older females.
Soft tissue sarcoma – Soft tissue sarcomas can really vary in size, shape and appearance. Sometimes they grow rapidly, while other times they grow very slowly.
Mast cell tumor – Mast cell tumors are very common in dogs. They can appear as solitary or multiple nodules and most commonly are found on the trunk, around the anus and on the legs. Lymphoma – Lymphoma is one of the most common cancers in domestic dogs. While lymphoma is characterized by tumors of lymphoid tissue in the lymph nodes, liver, spleen, bone marrow or elsewhere, a skin (cutaneous) form causes raised, round-ish nodules that congregate in epithelial cells.
Melanoma – Melanomas are usually darkly pigmented masses that tend to show up in dark areas of skin. When melanoma growths are found on the nail bed or in the mouth, they frequently are malignant.
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.
Histiocytoma – Histiocytomas are typically fast-growing, dome-shaped growths that are most common in young adult dogs.
Again, this is just a partial list of the types of lumps and bumps that an owner may notice on his dog. A veterinarian is in the best position to help owners diagnose and, if necessary, treat any skin tumors.

Prevention
There is no realistic way to prevent 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.

Special Notes
Skin tumors are common in domestic dogs. They may be nothing more than a cosmetic bother, but they may reflect a much more serious medical condition. Either way, dogs with skin tumors should be seen by a veterinarian.

Symptoms & Signs

Introduction
Skin tumors are among the most common tumors in dogs. Fortunately, many of these masses are benign. Canine skin tumors have a number of causes. Many skin growths are likely to be either papillomas ("warts"), lipomas (fatty tumors) or sebaceous gland adenomas. Some of the most common skin and subcutaneous tumors in dogs include:

Tumors of Epthelial Origin: papilloma, intracutaneous cornifying epithelioma, squamous cell carcinoma, basal cell tumors/carcinoma, hair follicle tumors (trichoepithelioma, pilomatrixoma, trichoblastoma, others), sebaceous gland tumors, hepatoid gland (perianal) tumors, tumors of the sweat gland (apocrine gland tumors), ceruminous gland tumors and anal sac tumors.
Tumors of Mesenchymal Origin: soft-tissue sarcomas.
Round Cell Tumors: plasmacytoma, mast cell tumor, lymphoma, histiocytoma, transmissible venereal tumor.
Melanocytic Tumors: melanoma.
Papillomas
Papillomas are benign tumors of the skin and oral cavity mucous membranes. They are caused by site-specific papilloma viruses and tend to occur in young dogs (6 months to 4 years) and in immunocompromised older adults. These lesions often appear on the eyelids, in the genital region or on the lips, gums, tongue, palate and throat. Commonly called "warts," papillomas are more common in Cocker spaniels, Kerry blue terriers, Miniature schnauzers and pugs. They normally present as small, discrete round growths with a rough or pedunculated surface, and they often show up in large numbers.

Papillomas are contagious between dogs, but not to people or cats. Uncommonly, benign papillomas can metastasize to squamous cell carcinoma.

Sebaceous gland tumors
There are several different types of canine sebaceous gland tumors. Nodular sebaceous hyperplasia, sebaceous epitheliomas and sebaceous adenomas are benign tumors most commonly seen in older dogs – especially Poodles, Cocker spaniels, Miniature schnauzers and terriers (sebaceous hyperplasia and adenomas), and Lhasa apsos, Shih tzus, Siberian huskies and Irish setters (sebaceous epitheliomas). These benign masses can be solitary or multiple and usually are raised, firm, wart-like or cauliflower-like growths ranging from a few millimeters to several centimeters in diameter. They can be pink, yellow-ish or darkly pigmented and can be oily, ulcerated or alopecic (hair loss on and around the lesion). In dogs, they are especially common on the ventral abdomen (on the belly), although they can show up anywhere.

Sebaceous gland adenocarcinomas, which are malignant tumors, are much less common in dogs. They appear similar to the benign sebaceous gland tumors and normally are solid, firm ulcerated or reddened masses on the trunk, legs, head and eyelids, especially in older animals.

Lipomas
A lipoma is a benign fatty tumor usually comprised of mature fat cells in subcutaneous tissue. Lipomas are extremely common in middle-aged and older dogs, especially Dobermans, Labradors and Miniature schnauzers. These tumors are normally well-circumscribed, soft to firm masses in the subcutaneous tissue (just under the skin) and usually are movable. In some cases, lipomas become rapidly infiltrative into underlying muscle, tendon and fascia; these tumors should be surgically and aggressively removed. Treatment is only necessary when the tumor is cosmetically unacceptable, rapidly growing or interfering with mobility.

Mast cell tumors
Mast cell tumors are malignant, highly invasive and difficult to treat with complete success. They are the most common cutaneous (skin) tumor of dogs. Mast cell tumors can appear on the skin or in the underlying tissue. They take a variety of forms and can be bumpy or smooth, poorly or well circumscribed, soft or firm, hairless or ulcerated, red or dark, and solitary or in multiple places. They appear more commonly in older dogs and in certain breeds, including Boxers, Pugs, Boston terriers, Labradors, Weimaraners, Beagles, Chinese Shar peis and Golden retrivers.

When you groom or pet your dog, always be alert for any suspicious lumps or bumps, with or without accompanying or persistent sores.

Diagnosis & Tests

Introduction
Most pet owners will eventually find a lump somewhere on their dog's body. The lump may be something as simple as a pimple or an allergic reaction to an insect bite. On the other hand, sometimes skin masses are much more serious. Wise owners will have their dogs examined by a veterinarian to assess the significance of any skin bumps that they detect.

How Skin Tumors are Diagnosed
One of the most common procedures used to identify the makeup of a skin tumor is a fine needle aspirate. During this procedure, the veterinarian or her assistant will gently insert a needle into the mass, pull back on the stopper of the syringe and then squirt the extracted fluid and cells onto a glass slide for examination under a microscope. This is a quick and easy way to diagnose many skin tumors, especially fatty tumors called lipomas. A somewhat more complicated technique is to perform a biopsy. This involves surgically removing a piece of the mass and tissue surrounding it using a scalpel, local anesthetic and sedation. The pathology laboratory often can make a more definitive diagnosis from a biopsy tissue sample than from cells removed by fine needle aspiration. Another useful diagnostic tool is an impression smear. This simple procedure involves pressing a glass slide onto the surface of the mass and then examining the transferred cells under the microscope. A skilled veterinarian can identify many types of tumors from microscopic assessment of cells by these various methods.

Sometimes, however, the attending veterinarian will elect to surgically remove a mass rather than sampling only a piece of it. There are pros and cons to using this as a diagnostic approach, which the veterinarian can discuss with the owner. When removing a mass suspected of possibly being malignant, the surgeon attempts to remove the entire lump and a fairly wide margin of normal, non-cancerous tissue completely surrounding it. The sample is submitted to a pathology laboratory for microscopic analysis and determination of the precise cellular composition of the tumor. Of course, it is not always possible to remove the tumor and enough nearby tissue to be sure that all cancerous cells have been removed. This is especially true of masses on the face and lower limbs, where the often is not enough room around the tumor to get the wide margins that veterinary surgeons hope for.

Special Notes
It is important for the medical team to know exactly what type of mass they are dealing with, so that they can come up with the best management and treatment protocol for their patient. These diagnostic tools are usually quite successful in identifying the composition of the tumor.

Treatment Options

Introduction
Most pet owners will find a lump on their dog at some point in time. While these masses may be harmless, sometimes they masses are malignant, dangerous and require prompt medical attention.

Treatment Options
The options for treating - or at least for managing - skin tumors depends entirely upon the cause of the tumor. For example, benign fatty masses (lipomas) rarely require treatment, other than perhaps for cosmetic reasons if they bother the owner or are in a location that bothers the dog. Many owners decide to have lipomas removed because they do not like the look or feel of them on their dogs.

Most veterinarians recommend that malignant skin masses be removed at the first opportunity. Aggressive surgical resection, with wide margins around the tumor site, is typically the treatment of choice. The removed tissue will be submitted to a pathology laboratory to assess whether all of the tumor cells associated with the mass have been removed. If it appears that malignant cells extend close to the surgical margins, a second surgery may be necessary. Radiographs (X-rays) may be recommended to determine whether cancerous cells have spread to nearby lymph nodes or to other areas, particularly to the bone marrow and/or lungs. Blood tests typically will be conducted as well as part of treatment to assess the dog's overall health and response to treatment.

In many cases, radiation and/or chemotherapy treatments will be used in addition to or in lieu of surgical resection to improve the success rate – especially when wide surgical margins cannot be achieved. Owners must recognize that tumors can recur post-operatively, despite whatever heroic treatment efforts are taken by the veterinary team. Regular rechecks are important for dogs with malignant skin tumors, even after they are treated.

Prognosis
As with diagnostic and treatment protocols, the prognosis for dogs with lumps and bumps on their skin depends entirely upon the cause of those masses. A veterinary oncologist (cancer specialist) or dermatologist (skin specialist) may be consulted for advanced diagnostic and treatment protocols.