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thyroid cancer can affect dogs and cats

Dog Thyroid Cancer – Signs, Symptoms, & Life Expectancy

It is never easy to hear that your furry friend has cancer. As pet parents, we worry about every lump and bump that we find. Thankfully, most of them are benign. Even the ugliest of lumps (the ones you are sure are cancer) are usually nothing to worry about.

Have you detected an unusual lump on your dog’s thyroid gland? Not sure where the thyroid gland is located?

The gland is in the neck near the trachea. If you have found a lump, try not to panic. It’s vital that you bring your dog to a veterinarian ASAP for an accurate diagnosis.

If you’re dog has been diagnosed with thyroid cancer, this post will take care of all your questions and concerns. This includes information about the thyroid gland and its importance, signs, how a diagnosis is made, the stages of cancer, and the ultimate prognosis/life expectancy.

The Dog’s Thyroid Gland – What It Does

The thyroid gland, located in the neck near the trachea (windpipe) and has two lobes, one on each side of the trachea. It’s controlled by the hypothalamus and the pituitary gland, located at the brain’s base.

Without a thyroid gland, the body wouldn’t be able to maintain regular metabolic activity. People and/or pets with a condition known as hypothyroidism (Hashimoto’s Thyroiditis) tend to feel tired and sluggish because of this.

The hormones released by the thyroid gland are essential in controlling the metabolism of cells. The organs that rely on the thyroid hormones are the heart, liver, kidneys, muscles, and nervous systems. 

Recognized Thyroid Disease in Dogs

It’s important to understand that disorders of the thyroid gland are complicated. Even diagnosis can be tricky. The 3 main types of thyroid disease in dogs include:

Hypothyroidism in Dogs

This means the dog has an underactive thyroid. It is a common disorder in dogs. Signs include fatigue, weight gain, haircoat, and skin changes.

Hyperthyroidism in Dogs

This disease increases a dog’s metabolism. This endocrine disorder causes the body to produce too much of the thyroid hormone. Signs include weight loss, anxiety, and diarrhea. Hyperthyroidism is rare in dogs.

Lymphocytic Thyroiditis

This is a common condition in dogs that actually leads to hypothyroidism. It’s thought that more than 50% of hypothyroidism in dogs develops from lymphocytic thyroiditis.

Evidence suggests it could be a disease caused by defective immunoregulation. An ultimate reason hasn’t been determined. Some factors that contribute to thyroiditis including excessive salt (iodine) is a factor in other species.

Read more about this form of thyroiditis below.

About Thyroid Cancer in Dogs

Thyroid cancer is considered rare in dogs and it’s still entirely known what causes it. It occurs when an abnormal cell forms in the thyroid gland, which creates more cells that are abnormal. The cells grow quickly and take over the normal cells, eventually blocking the thyroid gland from working properly.

The most common form of thyroid disease in dogs is lymphocytic thyroiditis.

This condition causes a dog to produce too many thyroid hormones. It can cause weight gain, irritability, thickening of the skin and coat, hair loss (alopecia), increased thirst (polydipsia), and increased urination (polyuria).

While the thyroid gland is essential for all dogs the last thing you want is for it to produce too much of a good thing.

Thyroid cancer can spread to the lungs

Two Important Hormones Released by the Thyroid Gland

Thyroxine (T-4)

Responsible for normal growth and development.

Triiodothyronine (T-4)

Helps to regulate metabolism.

If a dog develops thyroid cancer, the growing tumor blocks the normal function of the thyroid gland. This makes it very difficult for the dog to keep up with daily activities.

Thyroid cancer must be treated as soon as possible to prevent it from spreading to other parts of the body.

Thyroid Cancer in Dogs vs Thyroid Gland Function

A thyroid tumor doesn’t necessarily affect how the thyroid gland actually functions. However, it is possible for your dog to have hypothyroidism or hyperthyroidism at the same time.

Signs & Symptoms of Thyroid Cancer in Dogs

Unfortunately, dogs with thyroid tumors may have no signs of disease. There could be a mass on the underside of the neck, but it may not be immediately noticeable to the pet parent. If there is a tumor that compressed the windpipe (trachea), it can cause coughing, difficulty breathing (rapid breathing or shortness of breath).

If the tumor presses on the esophagus, the dog may begin gagging or have difficulty swallowing.

Other Signs of Thyroid Cancer in Dogs Include:

  • Facial swelling
  • Change in the sound of their bark
  • Loss of appetite
  • Weight loss
  • Lump or painless swelling in the neck area
  • Bleeding or discharge from the eyes or ears.

In the rare occurrence of hyperthyroidism, the dog may experience a rapid heart rate with an abnormal rhythm.  Signs include rapid heart rate and abnormal rhythm.

Dogs with hyperthyroidism will also have increased hunger and thirst. Muscle tremors are also possible.

Can Thyroid Cancer Spread to Other Parts of the Body?

Unfortunately, thyroid cancer can spread to other parts of the body. The most common sites of metastasis (spread) include the heart, lungs, and central nervous system.

Much like lymph nodes in people with thyroid cancer, a dog’s lymph nodes can become enlarged and swell in areas near the thyroid gland, which may indicate the spread of the tumor to those regions.

Breeds Predisposed to Thyroid Problems

Golden Retrievers are at increased risk of developing two types of canine thyroid cancer: anaplastic thyroid cancer and lymphocytic thyroid cancer.  One reasons for a higher prevalence in Golden Retrievers has to do with genetics. Some Golden Retrievers may have a higher concentration of thyroid cells due to a mutated gene.

It’s important to note that while environmental exposures may play a role, it doesn’t mean they are responsible for all cases related to Golden retrievers. About half of these dogs won’t develop any tumors at all during their lifetime.

Half of all thyroid cancers in dogs are diagnosed in the following breeds:

  • Bernese Mountain Dogs
  • Golden Retrievers
  • Keeshonden
  • Standard Poodles
  • Mixed-Breed Dogs

Although these dogs may be more likely to develop thyroid cancer, it can occur in any breed.

Diagnosing Thyroid Cancer in Dogs

If you suspect your dog may have a tumor or an enlarged thyroid gland, do not hesitate to take him/her to the veterinarian.

Tumors are diagnosed with a physical examination and bloodwork. The veterinarian will also palpate around the neck looking for a mass or growth. The following are typical tests a veterinarian may suggest when seeking a diagnosis.

X-Rays and Ultrasounds

To determine whether your dog is suffering from thyroid cancer, your veterinarian will conduct a physical exam and review your pet’s medical history, including potential exposure to pesticides and radiation. Your vet may also use imaging procedures such as X-rays and ultrasounds.

Blood Test

A blood test is often necessary to confirm a diagnosis of thyroid cancer in dogs. Blood tests are essential because sometimes tumors elsewhere in the body release substances that circulate throughout the bloodstream and elevate certain hormones, such as thyroxine (T4).

Tissue Sample/Tissue Biopsy

A definitive diagnosis of thyroid cancer is only made after analyzing a tissue sample from the tumor during surgery or some other form of biopsy.

Abdominal Ultrasound

Abdominal ultrasound (radiography) is a painless and safe way for a veterinarian to view the dog’s organs. If cancer is suspected, an abdominal ultrasound can help determine whether the cancer has spread.

The most common sign of thyroid in dogs is a mass in the neck.

Staging Thyroid Cancer in Dogs

After making an initial assessment, veterinarians will perform additional diagnostics to determine the stage to develop a treatment plan.

Staging is used to determine how much the cancer has grown or spread. When staging the thyroid cancer, the veterinarian may also want to do additional bloodwork, urinalysis, and chest x-rays.

Unfortunately, about 40% to 50% of dogs with thyroid cancer will have metastasis (spreading) to other parts of the body. – source: VCA Canada – Know Your Pet

The 5 Stages of Canine Thyroid Cancer:

Early Stage

Cells are only slightly abnormal. The tumor is small, well defined, and encapsulated; it may be removed entirely via surgery and radiation therapy (also called “thyroid remnant ablation”).

Intermediate Stage

Cells continue to divide without control, but the tumor has not yet invaded nearby tissue or produced distant metastases; treatment here varies from those in later stages depending on specific characteristics that will be identified during testing.

Late Stage

This type can spread into nearby organs as well as produce distant metastasis, either within the same organ or to different parts of the body such as bone, liver, lung, lymph nodes, or the central nervous system; if this is the case, then surgery can no longer be used for treatment. 

Terminal Stage

It may develop into an aggressive form of cancer that results in widespread destruction; though not curable at this time, chemotherapy and radiation therapy are usually advised to slow down tumor growth.

End Stage Disease

Thyroid cancer has progressed significantly at this point, and damage has been done to major organs such as the liver and heart.

In addition, lesions that produce high calcium levels have been detected in 90% of all dogs with thyroid tumors by this time, which affects how they function usually. At best, you will be prescribed pain relievers for your pet’s comfort.

Several factors contribute to the classification of canine thyroid cancer, but most importantly, they determine which treatment options are best for each case. For example, how far the tumor has metastasized and its location on the body will affect what types of therapies it can be treated with.

There are some physical characteristics you should keep an eye out on as well; if your pet has one or more of these signs of cancer, then you should inform your veterinarian right away:

  • . Enlarged lymph nodes (particularly in the neck)
  • . Vision problems due to pressure on the optic nerve
  • . Resistance when swallowing food
  • . Presence of fluid building up in the abdominal cavity causing distention breathing due to tracheal collapse.
Most thyroid tumors in dogs are malignant

Treating Thyroid Cancer in Dogs

For dogs that are diagnosed with early-stage thyroid cancer, the prognosis is excellent. If found in time, surgical removal (thyroidectomy) followed by radiation therapy is often effective in eliminating the tumor.

This treatment option becomes less successful when tumors have progressed into their late or terminal stages. It can be challenging to remove all of the cancerous cells, along with healthy surrounding tissue, without compromising your dog’s quality of life.

Surgery

If the tumor hasn’t spread to surrounding tissues and is loosely attached (movable), surgery may be recommended. This option would be considered if there was a reasonable expectation that all of the cancer cells could be removed, including some of the surrounding tissue.

The reason some of the surrounding tissue is taken is to eliminate the possibility of spread (if it hasn’t already).

Radioactive Iodine

Radioactive iodine is used in people and dogs with thyroid cancer. It’s performed by placing a radioactive tag on iodine and inserted into the body. The iodine is slowly absorbed by the thyroid gland which then destroys cancerous tissue.

This option can be used in dogs where surgery is not a great option. It can also be used if it’s found that the cancer has spread. Unfortunately, this type of therapy requires high doses of radioactive iodine to work effectively.

Used alone, radioactive iodine may not be as effective. As a result, it can be combined with chemotherapy and traditional radiotherapy. Complications of radioactive iodine therapy are rare but may include:

  • Inducement of hypothyroidism
  • The treatment may not work as planned
  • Kidney dysfunction or renal failure

Important Side-Note on Radioactive Iodine Therapy Recovery for Dogs

Dogs need to be confined for two weeks once treatment has been administered. There will still be high levels of radiation in the dog’s bloodstream. As a result, he/she cannot be in contact with you. In fact, it’s against the law to allow a dog treated with radioactive iodine to be near children under the age of 18 or pregnant women.

Complications of Surgery and Radiation Therapy

Before recommending a treatment option, the veterinarian will take into account a few things including:

Dog’s Age

Pets over ten years old generally have a higher risk of complications from anesthesia and surgery because they age faster than younger animals. In addition, there could also be pre-existing health problems that may complicate the condition.

Tumor Size

Larger tumors are challenging to treat. Dogs with tumors around their necks and shoulders have a higher risk of surgical treatment failure.

Cost of Surgery & Follow-Up Medication

When adding up the costs of thyroid cancer treatment, you have to take into account a number of things including:

  • The type of chemotherapy medication used
  • The number of rounds of chemotherapy required
  • The size of the dog

Cost of Chemotherapy for Dogs with Thyroid Cancer

Generally speaking, each round of chemotherapy treatment is approximately $1000. Multiply that times the number of rounds required.

Cost of Surgery for Dogs with Thyroid Cancer

The cost of surgery in dogs with thyroid cancer runs at about $3000, not including any medication or follow-up costs. Ultimately, the total cost will vary ($2500 – $6000) depending on the geographic location.

Cost of Radiation Therapy for Dogs with Thyroid Cancer

Radiation is usually given twice a week for five weeks (approximately). You can expect the final cost to be anywhere from $5000 to $7000. Again, price will vary.

Cost of Thyroid Medication for Dogs

Once the thyroid gland is removed, synthetic hormones need to replace the natural hormones now lost. The name of the drug commonly used is levothyroxine. It is a man-made hormone used in countless individuals (people and pets) with success.

Pet meds for thyroid cancer in dogs average about $30-$50 monthly. Pet insurance can help lessen some of the financial burdens.

What is the Life Expectancy of a Dog With Thyroid Cancer?

The life expectancy of a dog with thyroid cancer depends on the type and stage of cancer, but in general, dogs with thyroid tumors may live anywhere from six months to several years.

Older dogs are generally less likely to survive longer than younger dogs, based on other diseases that may be present. The prognosis is usually better for thyroid tumors that are small and not too invasive.

Final Thoughts

Breeds at high risk of thyroid cancer, including Golden retrievers, often develop the disease when they are young (8-12 months rather than nine years). On average, 80% of these dogs will experience reoccurrence within one year of surgery.

Surgery is generally successful, but there is a high chance of reoccurrence, and sometimes cancer has already metastasized before it is detected.  

Sadly, the prognosis for dogs with thyroid cancer that has spread to other parts of the body is poor. The key is catching the disease as early as possible, before it has had a chance to spread.

I want to thank you for taking the time to read this post. I wish you and your dog many years of happiness and health.

SOURCES:

Merck Manual Veterinary Manual – Hypothyroidism in Animals

Pubmed.ncbi.nlm.nih.gov – Lymphocytic thyroiditis

Animal Cancer & Imaging Center – Pet Loss Support

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