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.