Skin Tumors in Dogs

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Article Written by Dr. Daniel A. Degner, Board-certified Veterinary Surgeon (DACVS)

Key Points

Skin tumors can be benign or malignant

A biopsy of the tumor is needed to make the diagnosis prior to surgery

Surgical removal of the mass is the best option in most cases and the prognosis is dependant on the type of the tumor


Anatomy of the skin

The skin is made of 2 major layers, the epidermis and the dermis. Beneath the skin is a fatty layer with connective tissue called the subcutaneous tissue. The epidermis consists of epithelial cells (cells that are stuck together). The deep layer of the epidermis is actively growing, producing cells that gradually move to the surface of the skin. The dermis is a connective tissue layer that contains hair follicles, sebaceous gland (oil-producing glands) and sweat glands.

 

Definitions

Commonly, terms are used interchangeably and mean the same thing.

Mass is a lump or growth in the body's tissues.

A tumor is a growth and can be benign or malignant

Neoplasm is a lump, mass, and tumor. This word means new ("neo") growth (plasm) of cells.

Cancer is a tumor that by definition is malignant.

Malignant tumor has cells that are invasive into adjacent tissues and can metastasize (spread) to other parts of the body

Benign tumor means that it does not spread and it is just an annoying mass.

Metastatic tumor is a tumor that spread from another tumor in the body.

Metastasize means spreading of a tumor to another part of the body (typically through the blood stream or lymphatics)

 

Types of skin Masses that originate in the skin

Histiocytoma is a benign button tumor that typically is pink, raised is relatively hairless. Believed to potentially be induced by a virus, these tumors commonly will resolve spontaneously in most dogs. These can look identical to a mast cell tumor.
Mast cell tumor is considered a malignant tumor, that is the "imitator of tumors". Therefore it can look like almost any type of tumor. In general, the "button" type of this tumor is a pink, raised, hairless tumor that may swell if it is pinched, rubbed or massaged.
Basal cell carcinoma, more commonly found in cocker spaniels, is almost always a benign tumor of the skin and originates from the deep layer of the epidermis called the basal cell layer. Because this basal cell layer also surrounds hair follicles and sweat or sebaceous glands, they can also originate from these structures. This tumor located within skin of the head, neck and shoulders, is well-circumscribed, may be black in color.

Epidermal inclusion cyst is an accumulation of sebaceous gland secretions in a pocket within the skin or in the subcutaneous tissues. This is really not a tumor, but will feel like one. Sometimes these masses will rupture to the surface and the greasy central material of the mass will leak. These masses can become infected and be very painful to the pet.

Calcinosus circumscripta is a deposit of calcium within the skin. Secondary inflammation may also be seen. This mass, although not a cancer, may mimic the appearance of such. They commonly are very firm masses located almost anywhere on the body. These may be secondary to trauma, injections, and foreign bodies.
Melanomas, when located anywhere except in the mouth, lips, and toenail beds, have a low spread rate. When located in latter 3 sites, they commonly have a high tendency to spread to regional lymph nodes and the lungs. These tumors sometimes are black, yet other times do not have the black color as they have little pigment within the cells.
Plasmacytoma (extramedullary form) when found on the skin commonly is a benign mass. This type of tumor is malignant if it has spread from another part of the body. In order to prove that this type of tumor has not spread from the bone marrow to the skin, additional tests should be done to make sure that this the the case (bone marrow biopsy, serum electrophoresis, and evaluation of the the bones for tumor lesions with x-ray, CT, or bone scan). This tumor may appear to be a pink nodule within the skin.
Squamous cell carcinoma s a malignant cancer of the skin. This tumor is firm, nodular, frequently ulcerated, and extend deeply into the dermis of the skin. This tumor is locally invasive, but the spread rate is relatively low to moderate, depending on its site on the body.
Hair follicle tumors exist in two main forms: the trichoepithelioma and the pilomatricoma. Both of these are benign. They are typically hairless and look like a basal cell carcinoma.  
Sebaceous gland tumors originate from the oil producing cells in the skin. Sebaceous adenomas are benign, small, pink, lobulated (bumpy), and on the skin surface. Sebaceous epithelioma are benign masses that are most commonly found on the margin of the eyelids. Sebaceous gland carcinomas (see photo right) grow quickly, frequently are ulcerated, locally invasive and have a variable spread rate to other regions on the body.
Soft tissue sarcomas are malignant tumors that vary in their potential to metastasize. Grade 1 tumors have a 5 to 10% spread rate, grade 2 tumors have a 20 to 25% spread rate, and grade 3 tumors have a 50% spread rate. The growth rate may be slow or rapid and vary in their appearance. They commonly are not ulcerated, but as they outgrow their blood supply they can become ulcerated.

 

Diagnosis

Initial evaluation should first involve a fine needle biopsy of the tumor. A core biopsy of the tumor may collected if a fine needle biopsy is not providing a diagnosis. Chest x-rays and fine needle biopsy of regional lymph nodes is indicated in patients that have suspected cancer. Abdominal ultrasound may also be indicated to look for spread of the tumor to internal organs. Blood testing including a complete blood count and chemistry profile, and a urinalysis should be done to evaluate the patient's internal organ health.

 

The day of surgery

Please make sure that your companion has been fasted prior to surgery and that the prescribed dose of Pepcid AC has been administered. The surgeon will contact you after the surgery to give you a progress report on your companion after the surgery. Our anesthesia and surgical team will prescribe a pain management program, both during and after surgery that will keep your companion comfortable. This will include a combination of general anesthesia, injectable analgesics, local anesthetics, oral analgesics and anti-inflammatory medication.

 

Treatment

The hair coat surrounding the tumor is clipped. Cancerous tumors mandate removing the tumor and about an inch or more of normal tissue surrounding the tumor. Benign tumors can be removed by only removing the tumor and a small amount of normal tissue surround the tumor.

 

Aftercare

Following surgery, the patient will receive pain-relieving medication to ensure a comfortable recovery. A combination of nonsteroidal anti-inflammatory, local anesthetics, and narcotics may be needed to control pain. At home, the incision should be checked for signs of infection. Your pet should not lick the incision, as this could open the incision or cause infection. If necessary, an Elizabethan collar can be placed on your companion to prevent licking and chewing at the surgical site. Antibiotics may be indicated after the surgery in some cases. Exercise should be restricted for about 3 weeks after surgery.

Frequently Asked Questions After Surgery

When should my dog have the first bowel movement after surgery?

  • Many dogs will not have a bowel movement for the first 4 to 5 days after surgery
  • Reasons that a dog will not have regular bowel movements after surgery include:
    • The dog has been fasted prior to surgery
    • Dogs do not eat well during the hospital stay
    • They frequently do not eat well when they go home
    • They are fed highly digestible food that produces little stool
    • Pain medication that contain narcotics (such as morphine, fentanyl patches, and tramadol) can be constipating
  • If a pet does not have a bowel movement on the 5th day of being home, a stool softener such as metamucil can be fed
    • Dose of metamucil is 1 tsp per 25 Kg mixed in with each meal (canned dog food); feed immediately after mixing, as the metamucil will gel the food and may make it less palatable

My pet had surgery and will not eat.  What can be done?

  • Dogs
    • Most pets will not eat their regular dog food after surgery, especially if it is kibble.
    • Offer a cooked diet having a 1:1 ratio of a protein source and carbohydrate source.  The protein source can be any meat (example: chicken breast, turkey breast, lean hamburger) that is low in fat and should be cooked (drain off all fat after the meat has been cooked).   The carbohydrate can be pasta, potato or white rice.
    • Try canned dog food; to enhance the flavor sprinkle a very small amount of garlic powder or chicken or beef broth (Chicken-in-a- MugTM or Beef-in-a-MugTM products)
    • Try Gerber strained meats for babies such as the chicken, beef, turkey, or veal
    • Try Hill's A/D diet available at most veterinary hospitals
    • Hand feeding: place a small amount of food in the mouth so that your dog gets the flavor
    • Warm the food slightly in a microwave, as the food will be more aromatic; stir the food before feeding and test the temperature on the bottom side of your wrist; it should only be luke warm.
    • Remember that most pets will not eat the first day or two after they get home from surgery
  • Cats
    • Offer smelly foods that contain fish such as tuna or smelly cat foods
    • Try Gerber strained meats for babies such as the chicken, beef, turkey or veal
    • Hand feeding:  with your finger place a small amount of food on the roof of your cat's mouth; use a syringe to get soft food into the mouth
    • Warm the food slightly in a microwave as the food will be more aromatic; remember to stir the food before feeding and test the temperature; it should be only luke-warm
    • Some cats will only eat dry food, try kibble if your cat normally has been fed that food
    • Petting and stroking your cat frequently will help to stimulate appetite
    • Remember that most pets will not eat the first day or two after they get home from surgery
    • Appetite stimulants such as cyproheptadine may be helpful
    • If your cat refuses to eat anything for 7 days a stomach tube or nasogastric tube should be placed to provide nutrition so that a serious liver problem (hepatic lipidosis) does not develop

My pet is vomiting.  What can be done?

  • The first thing for you to discern is whether your pet is vomiting or regurgitating.  Both will result in fluid or food being brought up.  Vomiting always will have heaving or retching of the abdomen prior to expulsion of the vomitus.  Regurgitation is not associated with heaving and the pet usually just opens the mouth and fluid or food will be expelled.  Usually the regurgited material will be clear or brown colored fluid. 
  • Next is to identify the cause of the vomiting or regurgitation.
  • Causes and treatment of vomiting after surgery
    • When some pets return home after a stay in the hospital they may drink excessive amounts of water at one time and then vomit; if this appears to be the case, the water should be limited to frequent smaller amounts.
    • Medications such as antibiotics, narcotics or nonsteroidal anti-inflammatory medication commonly cause vomiting after surgery.  In order to see which medication is causing the problem, the administration of each drug should be separated 2 hours apart.  Usually the pet will vomit or appear nauseated (drooling and sick look) within 1 hour of administration of the medication that they are sensitive to.  The antibiotic in some cases may be changed to a different one, or may be discontinued. 
    • Stomach upset from anesthesia is a potential cause of vomiting and will pass within a couple of days. 
    • An uncommon cause of vomiting after surgery is internal organ failure.  Blood testing will confirm this problem. For this reason vomiting should not be ignored if it persists for more than 24 hours.
    • If your pet had surgery of the bowels or stomach, vomiting is always a concern, as it may indicate that infection of the abdominal cavity, called peritonitis, is present.  Do not ignore this sign.
    • Symptomatic treatment of vomiting involves withholding food for 12 to 24 hours, then introducing small amounts of bland food such as rice and lean cooked hamburger, if your pet does not vomit after that then gradually wean him/her back onto the regular diet after 3 days.  In order to decrease the acidity of the stomach, Pepcid AC 0.5 mg/kg can be given by mouth twice daily for 5 days.  Metoclopramide and Cerenia are good anti-vomiting medications for dogs and cats.  You should always consult a veterinary healthcare professional before administering medication.
  • Causes and treatment of regurgitation after surgery
    • The most common cause of regurgitation is reflux of acid from the stomach into the esophagus while your pet is under anesthesia.  Acidic fluid from the stomach can cause a chemical burn of the esophagus and result in a bad case of heart burn, called esophagitis.  This results in poor motility of the esophagus, therefore water and food will accumulate in this structure.  In most cases, esphagitis is self-eliminating and will resolve within two or three days. 
    • If the esophagitis is severe the esophagus may develop one or more strictures.  A stricture is a narrowing or stenosis of the esophagus and does not allow passage of food down the esophagus, in regurgitation that lasts longer than one week.  This problem should be brought to the attention of your pet's doctor within the first two weeks so that it can be treated by ballooning the stricture (minimally invasive procedure, as it is done with the aide of an endoscope).  If an esophageal stricture is chronic surgery is needed.
    • Symptomatic treatment of regurgitation caused by esophagitis includes feeding bland food, and administering a coating agent (sucralfate) and an acid blocker (omeprazole or other).  Consult a veterinary health care professional if the regurgitation continues for more than a couple of days.

How do I know that my dog is in pain following surgery?

  • Signs of pain include
    • crying
    • biting if you get near the surgical site
    • grimacing (lips are pulled back and the the dog looks anxious)
    • tragic facial expression
    • panting
    • restlessness and unable to sleep; pacing
    • if abdominal surgery was done the pet will not lie down on the incision, or will continually sit up in spite of appearing very tired
    • the worst pain will be for the first 2 to 3 days after surgery

What can I do to control my dog's pain?

  • Narcotic medications that control pain: tramadol, butorphanol, Duragesic (fentanyl patch)
  • Anti-inflammatories used to control pain: Deramaxx, Rimadyl, Previcox, or Etogesic
  • If an orthopedic surgery has been done cold packing the surgical site may be helpful
    • A cold pack may be a pack of frozen peas, crushed ice in a Ziploc bag, or a cold gel pack; place a thin barrier between the skin and the cold pack.  An alternative to a cold pack is to freeze water in a styrofoam cup; after frozen cut the bottom of the styrofoam cup out. Cool the surgical site around the incision by rubbing the exposed ice directly on the skin in a circular pattern.  Cooling the surgical site helps to numb the area.

How do I know that my cat is in pain following surgery?

  • Pain is more difficult to assess in cats versus dogs, as signs can be more subtle and they usually do not vocalize when in pain
  • Signs of pain in a cat include the following:
    • biting if you get near the surgical site
    • growling or deep cry
    • not wanting to eat
    • hiding and not wanting to be near owner (remember that this could also be caused by the cat just being upset about leaving home and coming back)

What can be done for pain at home for my cat?

  • Pain medication such as buprenorphine or a Duragesic (fentanyl) patch
  • Tylenol will kill a cat as they lack abundant glutathione enzyme in the liver
  • Anti-inflammatories can be used, but the dose is much less than dogs

Is it okay for my pet to lick the incision?

  • If a dog licks the incision, the healing process may be delayed.
  • Licking can remove stitches and cause the incision to open
  • Licking can become a severe habit that is difficult to break
  • Licking can cause infection as the mouth has many bacteria
  • Dogs will frequently lick the incision when the owner is not watching such as at night time; if the skin looks red or excoriated the most common cause is from licking.
  • To stop your pet from licking the following can be tried:
    • Elizabethan collar can be placed on the neck; this will not help stop your pet from scratching at the region
    • Cervical collar (bite not collar) is a less awkward device and can be effective at stopping a pet from licking the surgical site
    • A tee shirt can be used to cover an incision on the chest or front part of the abdomen; gather the waist of the shirt up over the dog's back and wrap an elastic band around this part of the shirt.
    • A bandage or sock can be used to cover an incision on a limb; fasten the top of the sock to the dog's limb with tape.
    • Bitter apple can be applied around the incision; many dogs will continue to lick  after application of this topical
    • Bitter Apple and Liquid HeetTM (obtain this from a drugstore...it is used for sore muscles) mixed in a 2:1 ratio can be applied around the skin incision
    • Antipsychotic medication in some cases is needed

Board-certification by the American College of Veterinary Surgeons

What does it mean?

  • Four years of advanced training in surgery beyond the Doctor of Veterinary Medicine Degree

  • Experience in the development of new surgical treatments

  • Rigorous examination by the American College of Veterinary Surgeons to ensure competency in advanced surgical techniques

  • Assurance that a veterinarian is a surgical specialist

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