Medical Oncology: Canine Thyroid Carcinoma
What Is Thyroid Carcinoma?
There are two thyroid glands in the neck. They secrete thyroid hormone, which helps maintain energy, body weight, temperature, skin, fur, nail growth, and general metabolism. Thyroid carcinomas are cancerous tumors of this gland. Dogs can have one or both thyroid glands affected. Thyroid tissue can also grow anywhere from under the tongue, along the neck, and into the chest. Dogs can develop thyroid carcinoma tumors in those areas as well. Some thyroid carcinomas cause excess thyroid hormone to be
released.
What Are The Clinical Signs?
Many dogs with thyroid carcinoma have no signs. In others, a tumor is felt along the throat. Some dogs cough or have trouble swallowing food and water from the pressure of the tumor. If the tumor causes excess thyroid hormone production, dogs can show weight loss but have a good or even increased appetite, agitation, increased drinking/urinating, panting, and a fast heart rate. Large tumors can be painful.
What Diagnostics Are Performed?
If a tumor is felt around the thyroid gland, the next step is to image the area. This is done with an ultrasound or CT scan of the neck. To confirm a diagnosis a sample of the tumor is taken with a small needle, with ultrasound guidance. If the ultrasound shows large blood vessels within the tumor, this may not be recommended. Sampling could lead to bleeding and/or the sample may not be diagnostic.
Staging tests to look for spread include taking samples from lymph nodes near the tumor and imaging the lungs and abdomen. To do this, patients can undergo a CT scan of their neck, chest, and abdomen all at once. This same CT scan can be used to plan surgery and/or radiation (see “Treatment Options” below.)
Blood work is done as part of a general health screen and to examine for other health conditions before treatment. The dog’s thyroid hormone level is checked as well.
Treatment Options And Prognosis:
The best treatment for thyroid carcinoma is surgery. With complete removal, the prognosis can be more than 3 years and some dogs are cured. You may need to give your dog thyroid replacement medicine after surgery.
If the tumor cannot be removed with surgery, or you do not want to do surgery, radiation therapy is an option. This can stabilize or even shrink the tumor. The prognosis with more aggressive radiation therapy could be about 1-2 years. Palliative radiation therapy is less intensive, but the prognosis is shorter (5-6 months).
Chemotherapy is recommended for some dogs after surgery. This decision is based on the size of the tumor and the biopsy report. Chemotherapy is also recommended for dogs with thyroid tumors that have spread. There are both intravenous and oral options for treatment. The benefit of chemotherapy is generally unknown. Some dogs with metastasis can live for months as those tumors are typically slow growing.
Radioactive iodine (I-131) is an option for some dogs. It is injected into the patient and destroys cancerous tissue. This is a common therapy in cats with hyperthyroidism. Dogs need larger doses of I-131, so this option is limited due to cost and availability.
| Treatment | Indication | Treatment Schedule | Cost |
|---|---|---|---|
| Radiation Therapy Definitive | Pre-operatively: Large tumors where incomplete resection is likely Post-operatively: Incompletely excised tumors | Daily treatments for ~ 4 weeks | $4500-$6000 May require CT scan prior to starting treatment |
| Radiation Therapy Palliative | Non-resectable tumors | Varies: Typically, weekly treatments for 4-6 weeks | $1500-2500 May require CT scan prior to starting treatment |
| Chemotherapy: | |||
| Carboplatin | Metastatic disease, post-operatively for some tumors | IV treatment every 3 weeks for 4-6 treatments | $400 per treatment |
| Metronomic | Metastatic disease, post-operatively for some tumors | Daily oral medications at home | Varies depending on body weight Typically, ~$300-$400 per month |
| Tyrosine kinase inhibitor (Palladia®) | Non-resectable tumors, metastatic tumors, others | Oral medication given every other day at home | Varies depending on body weight Typically, ~$300-$400 per month |
What Are The Side Effects?
Side effects depend on the treatment selected and the extent of the disease and clinical signs. Surgery carries the risk of anesthesia, though this is minimal. Other risks include bleeding and complications from healing or infection. Side effects of chemotherapy are infrequent and most commonly include temporary gastrointestinal upset such as vomiting or diarrhea or temporarily lowered white blood cell counts. Decreased appetite and lethargy may also occur. Radiation therapy includes the use of anesthesia during treatments and side effects include gastrointestinal upset (vomiting, diarrhea), local skin/tissue irritation, and potential interference with surgical healing.
Your pet will be prescribed supportive medications for nausea (manifested by decreased
appetite, increased salivation, or drooling occur) and diarrhea for you to have on hand at
home to use if necessary. It is best to be proactive with these medications and provide
these as soon as signs are noted. Should you have any questions, your oncology team is
available to assist and develop a tailored plan for your pet.
How Do I Prepare?
We understand this is a difficult time and we are here to support you and your pet by
providing the options and care necessary. Selecting a therapy is not binding and can be
adjusted to you and your pet’s needs. You will be updated on your pet’s response to
treatment and plan.
Getting Started
Once you have determined the best therapeutic option for your pet, you will work with
our oncology team to develop an appointment plan.
Scheduling: Patients undergoing chemotherapy treatments must have a scheduled
appointment before arrival:
- Schedule your appointments at reception upon check out
- Drop-offs are requested between 7:30-8:30 am
- No discharges are done between 2:30 pm- 3:30 pm as our oncology team is in rounds