Skin Cancer in Dogs

Skin cancer (adenocarcinoma) is an overgrowth of cells that make up the sebaceous glands. Sebaceous glands are the oil secreting glands that lubricate the skin and fur. If cells that make up a gland overgrow, a firm, raised growth will appear on the skin. Skin adenocarcinomas are most frequently found on the eyelids, face and head, though they can appear anywhere on the body. The growth may be itchy and become red and inflamed, bleed, or develop an infection. Adenocarcinomas in dogs are often benign and surgical removal has a positive prognosis.The most common tumor appearance in dogs is the skin tumor. Not always correlated to frequent sun exposure, some breeds are at a higher risk of having skin tumors than others. This includes Boxers and Retrievers. Age does play a factor, with later stage adults and seniors being the most frequent to display symptoms. Tumors are grouped into two segmentations, benign (non-cancerous) and malignant (cancerous). If you notice a lump or build-up, on your dogs body (especially face), see a veterinarian as soon as possible.

Characteristics of skin adenocarcinoma in dogs:

• Common in dogs 7 years and older
• One or more “wart-like” growths on the skin, 2mm to 1cm in diameter
• May appear anywhere but frequently seen on eyelids, face or head
• Yellow, brown or black in color
• Loss of hair on and/or around the growth
• Itchiness
• Redness or inflammation
• Bleeding or ulceration
• May develop secondary infection

Types

Skin adenocarcinomas fall into three general types:

• Sebaceous Adenoma - Sebaceous adenomas are an overgrowth of sebocytes (the secreting cells of the sebaceous gland). The growth may extend into the subcutaneous tissues.
• Sebaceous Ductal Adenoma - Sebaceous ductal adenomas are formed from the sebaceous gland ducts and are made up of keratin and oil. They may extend deep into the dermis.
• Sebaceous Epithelioma - Sebaceous gland epitheliomas are comprised of the basal progenitor cells. They contain melanocytes and may appear dark in color.

Growths located on the eyelids arise from Meibomian sebaceous glands. These tumors are identical to those located elsewhere on the body but are referred to as “Meibomian adenomas.”

The exact cause of skin adenocarcinomas is unknown. These growths are not infectious and not transmitted between animals or from animals to humans. Risk factors include:

• Hormonal dysfunction
• Age (dogs over the age of 7 years)
• Genetic predisposition (breeds include Basset Hounds, Beagles, Cairn Terriers, Cocker Spaniels, Dachshunds, Miniature Poodles, Samoyeds, Shih Tzus, Siberian Huskies, and West Highland White Terriers)

If you notice a lump on your pet’s skin, it is always a good idea to schedule an appointment to bring the pet in for an examination. It is very important to bring your pet to the veterinarian if you notice a growth changing in size, shape or color or if you notice bleeding or pet discomfort (itching, chewing at the site).

Visual examination of a skin mass can give the veterinarian an idea of the type of growth. Definitive diagnosis is made through microscopic examination of tissue.

Tissue Collection Methods:

• Fine needle aspirate – a needle is inserted into the mass to collect contents. The contents are ejected onto the surface of a microscopic slide for examination.
• Biopsy – a small portion of the mass is removed and placed in formalin (or other preservative) to be examined.
• Impression Smear – a microscopic slide is pressed against the mass (often used with ulcerated masses) to transfer cells for examination.

Tissue Examination Methods:

• Cytology – a slide preparation is examined for the presence of abnormal cells. Often used for rapid or preliminary screening.
• Histopathology – examination of tissue that has been prepared and stained. Samples are often sent to a laboratory for examination and diagnosis by a veterinary pathologist (may take longer than 24 hours).

X-rays or ultrasound may be performed to rule out the presence of internal masses or metastasis.

Once the veterinarian has examined the growth and cytology, the most common treatment route is surgical removal. The majority of skin adenocarcinomas are benign, technically an overgrowth of cells rather than a malignant tumor with metastatic potential.

Surgical Removal

Surgical removal of small growths can be done under local anesthesia during the veterinary appointment in most cases. Anesthetic is injected in and around the growth under the skin. After a few minutes, the growth is cut from the skin with a surgical blade and the area sutured closed and bandaged.

General

Surgical removal of larger growths, growths in vulnerable areas (like the eyelid, nose, ears), or growths deep under the skin may require general anesthesia for surgical removal. An appointment will be made for another day and the pet will undergo surgery to remove the growth and be released the same day if there are no complications.

Histopathology

After surgical removal, the veterinarian may send the growth out for histopathology to determine that the entire mass was indeed excised.

Radiotherapy/Chemotherapy

If a skin adenocarcinoma is determined to be malignant, radiotherapy and/or chemotherapy may be used to destroy any remaining cancer cells and prevent growth in other areas.

Rate of regrowth is low with benign skin adenocarcinomas as long as the entire mass has been removed. Skin adenocarcinomas tend to develop on numerous areas of the skin throughout the years so the pet may require future growths to be removed.

Sebaceous epitheliomas have a higher rate of regrowth and may recur after surgery.

If your pet has had a growth removed, he may need to revisit the veterinarian weekly for 2-3 weeks to examine healing. Your pet may need an Elizabethan collar (e-collar or cone) to prevent scratching at or licking the incision site.

Be sure to administer any pain medications and/or antibiotics as directed by your veterinarian to keep the pet comfortable and prevent infection. The incision site should heal within 2-3 weeks if no infection or difficulties arise. Report any bleeding, redness, swelling or loss of sutures to your veterinarian.

In cases of malignant tumors, your veterinarian may recommend ongoing chemotherapy or radiation treatment and follow up x-rays.

There is no method of prevention of skin adenocarcinoma. Always examine your pet’s skin for any new growths or changes in current growths and report these to your veterinarian.