Thyroid Cancer in Dogs

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

Key Points

The most common sign of a thyroid tumor is a swelling or lump in the neck region

Thyroid tumors usually are malignant and have a high tendancy to spread

Surgery is best suited for tumors that are freely moveable

Tumors that are invasive or fixed to the tissues of the neck should have radiation therapy

Chemotherapy is usually recommended as an adjunctive treatment for thyroid tumors


Introduction

  • Dogs have two thyroid glands that are located along side of the windpipe in the region of the neck. This gland produces thyroxine, a hormone that regulates the body’s metabolism. Thyroid tumors in dogs are relatively uncommon. Golden retrievers, Beagles, and Boxers between the ages of 9 and 11 are most common to develop this tumor. These tumors are almost always malignant, meaning that they tend to spread to the lungs and lymph nodes and can grow into nearby structures such as the windpipe, blood vessels and esophagus. At the time of diagnosis, 35 to 40% of the dogs will have visible evidence of spread of the tumor to other parts of the body (especially the lungs). As high as 60% of dogs will have the cancer affect both thyroid glands, which causes the glands to malfunction in 50% of these cases. In about 10% of the cases, the tumor will produce excessive amounts of thyroid hormone which can have systemic side effects.

Signs and Diagnosis

  • The most common clinical sign of this tumor is a mass in the neck. Other signs usually are attributable to the tumor affecting the nerves of the voice box and may include a change in the tone of the bark, harsh breathing sounds, difficulty breathing, and rapid breathing. If the nerves that control swallowing have been affected or the esophagus is compressed by the tumor, difficulty swallowing may be noted. Other less common findings include bruising under the skin and swelling of the head. If the tumor produces excessive amounts of thyroid hormone, weight loss, marked increased appetite, muscle wasting, increased thirst and increased urination may be seen.
  • A complete blood count, chemistry profile and urine testing are completed in the initial stages of the evaluation of the patient that has a suspected thyroid tumor. Blood tests can be run to see if the thyroid glands are functioning normally or are hyperactive. A fine needle biopsy of the tumor provides a diagnosis about 50% of the time. Ultrasound of the neck frequently can show the extent of the tumor and demonstrate if the tumor has spread to lymph nodes in the neck. Chest x-rays are important to rule out visible spread of tumor to the lungs.

The Day of Surgery

  • In preparation for surgery, your pet should be fasted starting at 10 PM the night before surgery, however water does not need to be with held. To help prevent heartburn after surgery, a single dose of Pepcid AC (10 mg tablet per 20 pounds of body weight) should be administered at 6 AM at home on the day of 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, and oral analgesics.

Treatment

  • It has been estimated that only 25 to 50% of patients that are presented with a thyroid tumor are candidates for surgery. Only tumors that are not attached to the underlying tissues in the neck should be attempted to be removed. Providing that no visible spread of the tumor can be detected, dogs that have a freely moveable tumor removed can expect to live for another 3 years versus about 6 to 12 months for tumors that are invasive and fixed to underlying tissues.
  • Radiation therapy is used to treat thyroid cancer that is invasive into underlying tissues. Even with these aggressive tumors, the prognosis still can be favorable with 72% of the patients reported to survive 3 years following treatment, providing that there is no visible metastasis.
  • Following removal of these thyroid tumors, chemotherapy is definitely indicated if the resected mass is larger than 100 cm3, as the spread rate approaches 100% in these cases. Thyroid tumors tend to be partially responsive to chemotherapy, therefore, there is value in this treatment modality. Unlike humans, most dogs receiving chemotherapy do not loose their hair and usually have only mild side effects, which may include transient loss of appetite and vomiting.
  • Treatment with radioactive iodine can be successfully used to treat some thyroid tumors. Since this treatment requires a high dose of radioactive iodine, most hospitals do not offer this treatment due to staff safety concerns.

Aftercare

  • After surgery, you can continue to give your pet a prescribed pain reliever to minimize discomfort. In order to minimize bruising and swelling of the surgical site, apply a cold pack to the neck 20 minutes per session for four sessions daily during the first three days after surgery. Do not allow your dog to scratch the incision on the neck. If necessary the neck can be bandaged by one of our doctors to protect the incision. Use a harness to walk your dog instead of a collar so that no pressure is applied to the incision. Your pet may develop a fluid pocket in the region of the surgical site called a seroma, however, the body usually will naturally resorb the fluid over one month after surgery; restricting your dog’s activity for three weeks after surgery will help minimize this complication.
  • If your companion is recovering well following surgery and no complications develop, the healing process will be monitored by the surgeon with one follow-up exam scheduled two weeks after the surgery. Chemotherapy can initiated by our oncologist two weeks after surgery or at the time of radiation therapy.

References

  1. Carver JR, Kaptakin A, Patnaik AK. A comparison of medullary and thyroid adenocarcinomas in 38 dogs. Vet Surg 1995;24:315-319.
  2. Slensky KA, Volk SW, Schwarz T, et al . Acute severe hemorrage secondary to arterial invasion in a dog with thyroid carcinoma. J Am Vet Med Assoc 2003; 223:649-653.
  3. Fineman LS, Hamilton TA, de Gortari A, et al. Ciplastin chemotherpay for treatment of thyroid carcinoma in dogs: 13 cases. J Am Anim Hosp Assoc 1998; 34:109-12.
  4. Harari J, Patterson JS, Rosenthal RC. Clinical and pathologic features of thyroid tumors in 26 dogs. J Am Vet Med Assoc 1986; 188(10): 1160- 1164.
  5. Kent MS, Griffey SM, Verstaete FJM, et al. Computer-assisted image analysis of neovascularization in thyroid neoplasms from dogs. Am J Vet Res 2002; 63:363-369.
  6. Greco DS. Endocrine emergencies. Part II Adrenal, thyroid and parathyroid disorders. Comp Cont Ed Vet 1997; 19(1)
  7. Mayer MN, MacDonald VS. External beam radiation therapy for thyroid cancer in the dog. Can Vet J 2007;48: 761-763.
  8. Turrell JM, McEntee MC, Burke BP, Page RL. Sodium iodide I 131 treatment of dogs with nonresectable thyroid tumors: 39 cases (1990-2003). J Am Vet Med Assoc 2006;229:542-548.
  9. Theon AP, Marks SL, Feldman ES, GBriffey S. Prognostic factors and patterns of treatment failur in dogs with unresectable differentiated thyroid carcinomas treated with megavoltage irradiation. J Am Vet Med Assoc 2000; 216:1775-1779.
  10. Radlinsky MG. Thyroid surgery in dogs and cats. Vet Clin Small Anim 2007; 37:789-798.
  11. Barber LG. Thyroid tumors in dogs and cats. Vet Clin Small Anim 2007; 37:755-773.
  12. Klein MK, Powers BE. Withrow SJ, et al. Treatment of thyroid carcioma in dogs by surgical resection alone: 20 cases (1981-1989) J Am Vet Med Assoc 1995; 2006(7): 1007-1009.
  13. Withrow SJ, Vail D. Tumors of the Endocrine System in Small Animal Clinical Oncology pp 591-608.
  14. Pack LA, Roberts RE, Dawson SD, Dookwah HD. Definitieve radiation therapy for infiltrative thyroid carcinoma in dogs. Vet Radiology Ultrasound, 42(5):471-474, 2001.

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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