Tumors of the skin are probably the most common tumors seen in dogs and can be of many different types. Those that originate in the epithelium, the outermost layer of the skin, include papillomas (warts), cornifying epitheliomas found within the layers of skin, various forms of follicle cell tumors, tumors of the sebaceous glands, tumors of the sweat glands, hepatoid gland tumors also known as perianal tumors, anal sac tumors, squamous cell carcinoma, and basal cell tumors. We also encounter soft-tissue sarcomas, and various round cell tumors including plasmacytomas, mast cell tumors, lymphoma, histiocytoma and transmissible venereal tumors. Dogs can also develop melanomas, either malignant or benign.
Papillomas (warts) are benign, found on the surface of the skin or mucous membranes and caused by viruses that seem to target specific areas of the skin, the eyelids, in the genital region, on lips, gums, tongue, palate and throat. They may appear singly or in large numbers. They are most common in young dogs or older dogs with decreased immunity.
Dogs can get several different types of tumors associated with sebaceous glands (glands that secrete a lubricating substance). These are usually benign masses, solitary or multiple, raised and firm, and can be pink, yellowish or darkly pigmented. They can be oily, ulcerated and frequently the hair is gone around them. They are most commonly found on the belly, but can be anywhere on the animal. Sebaceous gland adenocarcinomas are malignant tumors and much less common in dogs. They usually are found in older dogs and appear similar to the benign form. A trained pathologist must make the determination of benign or malignant.
Lipomas are benign fatty tumors, usually found in the tissues just under the skin (subcutaneous). They are very common in middle-aged and older dogs, especially if the dog is a little overweight. They are usually well circumscribed, soft to firm to the feel and move easily within the tissue. Surgical removal should be considered if the lesion is cosmetically troubling or if it is growing rapidly or interfering with the dogs ability to move about. Sometimes lipomas infiltrate into underlying tissues; get these removed as soon as possible.
Mast cell tumors are malignant, invade surrounding tissues and difficult to treat successfully. They account for a little more than 20 percent of all canine skin tumors diagnosed. They are on the skin or in the subcutaneous tissues. They can be bumpy or smooth, easy or difficult to palpate the limits or edges, soft or firm, ulcerated or free of hair, red or dark and either singly or in multiple locations. They are found more commonly in older dogs who may show signs of metastasis and excessive histamine release, resulting in gastrointestinal distress, bleeding, delayed wound healing and, in final stages, shock. Most common sites of metastasis are lymph nodes, spleen, liver and bone marrow.
If your pet has any suspicious lumps or bumps, get it to your veterinarian as soon as you can. If the lesion is malignant, early detection is the key to successful treatment.
Dr. David Gross of Edmonds graduated from Colorado State University’s veterinary school in 1960 and was in private practice for 10 years. He retired in 2006 as Professor and Head of Veterinary Biosciences, at the University of Illinois, Urbana-Champaign. Dr. Gross is the author of “Animals Don’t Blush,” which describes the unique patients and even more unique clients of a veterinary practice in Sidney, Montana in the early 1960s. The book is available at the Edmonds Bookshop.