What is Thyroid Cancer?
Hyperthyroidism can cause tumors to form on the endocrine glands in the neck. These are noticeable lumps that you can feel upon rubbing the neck of an affected cat. The tumors are generally one of two types of cancer. Benign adenomas are the most common type of cancer related to hyperthyroidism. They are referred to as benign because this type does not metastasize (spread) to other body parts. Malignant adenocarcinomas are cancerous tumors that are aggressive and do spread throughout the body. Of the two types, benign adenomas are easier to treat. Either form of cancer tends to go untreated for quite some time, but the earlier it is caught and treated by a veterinary professional, the better. Failure to treat the condition can result in organ failure and death.
Feline thyroid cancer is a gradually developing cancer that is sometimes seen in older cats (usually above the age of twelve). It can take months or years to manifest. The thyroid consists of two lobes of endocrine glands in the upper neck. It is responsible for the production and secretion of the hormones thyroxine (T4) and triiodothyronine (T3), which regulate the pace of the metabolism and other body functions. When the thyroid starts to produce too many of these hormones, hyperthyroidism develops in the cat.
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Symptoms of Thyroid Cancer in Cats
The most common sign of thyroid cancer is a sudden, consistent surge in energy. While this may seem like a good thing, it can be the sign of an overactive thyroid. Monitor this, and watch for other symptoms, such as:
- Polyphagia (increased appetite)
- Polydipsia (increased thirst)
- Polyuria (frequent urination)
- Urination outside of litter box
- Diarrhea
- Vomiting
- Nausea
- Weight loss
- Change in behavior
- Increase in energy
- Restlessness
- Racing heart beat
- Heart murmur
- High blood pressure
- Dull fur
- Hair loss
- Incessant meowing
- Blindness (in very advanced cases)
Causes of Thyroid Cancer in Cats
When the thyroid begins to secrete excessive amounts of thyroid hormones, hyperthyroidism, and in turn, thyroid cancer develops. The exact cause is not fully understood, however, it is believed that a series of events and circumstances lead to cancer. Possible causes include:
- Diet consisting of too much iodine
- Environmental chemicals
- Radiation exposure
Diagnosis of Thyroid Cancer in Cats
If you or your veterinarian suspect thyroid cancer, an appointment should be made to investigate the cat’s condition. A full medical history will be needed to see if the cat has an extensive history of hyperthyroidism. A physical exam will be completed, with focus on the under chin and neck to feel for nodules under the skin. These can be noticeable lumps or chains of tissue. The vet will also take care to differentiate between thyroid cancer and diabetes, as they do share some symptoms.
Blood work will be needed, including a complete blood count and a biochemical profile. These tests will help see how many blood cells are present. T4 serum levels will be checked to see if they are registering higher than 10 times the normal amount. Another indication of cancer is if the cat has no response to either methimazole or carbimazole. The amount of thyroid hormones present in the body will be tested. Urinalysis may be done to exam the function of the kidneys and liver.
X-rays can show if the tumors present are irregular or multifocal, and can be used to monitor any spreading. Often, a scintigraphy will be requested, as it is useful for further assessing tumors and determining appropriate dosages for treatment. The cat will need to be kept at the clinic for 2-3 days after this test, as it uses radioactivity that stays present in the cat for a time. Cardiac ultrasound may be needed if heartbeat irregularities are found. If the cat’s condition is stable enough, an excisional biopsy (full removal of the tumor) will be performed. When microscopically evaluated, this can lead to a definite confirmation of cancer present.
Treatment of Thyroid Cancer in Cats
A few different treatments are available depending on the type of cancer present and how far it has progressed in the cat. Often, a combination of these treatments will be recommended for best results.
Radioiodine
Radioactive iodine has been found to be very effective in treating thyroid cancers. It is non-invasive and no general anesthetic is needed. A dosage of radioiodine is injected under the cat’s skin. It will treat all tissue that is hyper functioning in the body, and kill all abnormal cells. The cat will need to stay at the clinic or hospital for up to four days to eliminate all radioactive materials to be considered safe at home. A higher dose is given for cats with adenocarcinomas. This treatment has a 94% success rate.
Surgical Debulking or Removal
This treatment is often combined with radioiodine administration. At the time of biopsy, all tumors greater than 3-4cm in diameter will be removed. If congestive heart failure is occurring due to thyroid cancer, a full removal of the thyroid glands may be needed. This requires general anesthesia and is a higher risk surgery. Surgical complications are common.
Medication
In very progressed cases of thyroid cancer, medication to slow progression may be the only option. Antithyroid medication can reduce rapid onset of thyroid issues and lengthen life expectancy. These medications will need to continue for the duration of the cat’s life and can be expensive.
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Recovery of Thyroid Cancer in Cats
If the cat responds positively to radioiodine treatment, the general prognosis is very good. Extended survival lengths have been noted even in advanced cases of thyroid cancer. It takes 3-4 weeks to verify whether the treatment is fully successful or not. If it is, there is only a 0.3% chance of remission.
If the cat has undergone surgery, check frequently that the incision is clean and dry. The vet may prescribe calcium or vitamin D supplements for the healing process. In all treatments, the vet will monitor T4 levels in 4-6 weeks, and then periodically after that. Recurrence does happen, especially when radioiodine has not been administered. If the cat is not a good surgical candidate due to advanced cancer, a very restrictive diet may be prescribed to improve and lengthen lifespan.
Thyroid Cancer Average Cost
From 520 quotes ranging from $3,000 - $8,000
Average Cost
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Top
Thyroid Cancer Questions and Advice from Veterinary Professionals
Domestic shorthair
Cadbury
19 Years
25 found this helpful
25 found this helpful
My pet has the following symptoms:
Weight Loss
Hair Loss
No Appetite
Thirst
Urination Problems
Difficulty With Bowel Movements
My 19 1/2 yo cat has been on methimazole 5 mg twice daily since he was 3 or 4 years old. His T4 is extremely high and the calcium in his blood is also elevated. I run 150 ml fluids on him daily to keep his kidneys functioning. He also has calcification of the spinal canal at L7-S1 and has difficulty with bowel movements. What is the prognosis for treatment with radioiodine in a cat this old with the other conditions he is already being treated for?
Aug. 28, 2018
Answered by Dr. Michele K. DVM
25 Recommendations
Treatment with radioiodine would probably be a bad idea for Cadbury. That therapy tends to be reserved for cats with normal kidney function, and he seems to be managed very carefully for his conditions. It would probably be better to continue with the therapy you are using.
Aug. 28, 2018
As of this morning, Cadbury is now on prednisone to keep him comfortable. His kidney function is normal at this point, but his T4 was a whopping 34.6 and the calcium levels in his blood are also extremely high. I know it is just a matter of time, and I will keep him comfortable for as long as I can, but, unfortunately, the prognosis is grim. Thank you for your advice, and your caring attitude to our little furry friends.
Aug. 29, 2018
Cadbury's Owner
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Domestic shorthair
baby
11 Years
3 found this helpful
3 found this helpful
My pet has the following symptoms:
Swollen Lymph
I have an 11 year old cat who was dx with Lymphoma in March. We have undergone many different chemo tx's ranging from Lomustine (which did not work) to Vincristine which works! Problem is now we are down to q 3 weeks and the tumors are back at 2 weeks. He is also on methimazole for hyper thyroid . Thyroid seems under control at this time. Could he have not lymphoma but thyroid cancer?? His lymph glands around his neck are greatly swollen, but vincristine seems to take that down ... but every week!!! What choices do I have???
July 20, 2018
3 Recommendations
Without examining Baby and doing a few tests, I couldn’t confirm whether there is lymphoma or thyroid cancer; I don’t know which specific tests your Veterinarian performed to make the lymphoma diagnosis (lymph node aspiration etc…). If you have concerns about the diagnosis you should visit your Veterinarian for a discussion to ease any concerns you may have. Regards Dr Callum Turner DVM
July 21, 2018
There was a lymph node aspiration... looked like lymphoma. There was also a chest x ray and an MRI of abdomen. Nothing there. These were done by an oncologist which is too far away to get back there. Mylocal vet has been administering the chemo.
July 21, 2018
baby's Owner
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tabby
Missy
17 Years
2 found this helpful
2 found this helpful
My pet has the following symptoms:
Small Amount Of Blood Either From Nose
I have a female car that is 17 years old. She was recently diagnosed with thyroid cancer. She was out on Mehimazole tablets 5mg.1/
2 twice a day. We are traveling out of state and have noticed small amounts of blood on a pillow she sleeps on. Not sure if it's coming from her nose or tear ducks. Us this a sign of the cancer or what, what should I do?
June 3, 2018
Answered by Dr. Michele K. DVM
2 Recommendations
The blood droppings are not a typical sign of thyroid cancer, and are probably unrelated. It would be best to find a veterinary clinic near where you are travelling and have her examined to see where the blood is coming from, and if she needs any treatment for that.
June 3, 2018
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domesticshorthair
Susie
about 12 years old
4 found this helpful
4 found this helpful
My pet has the following symptoms:
Vomiting In The Past
To my knowledge my cat, thankfully, doesn't have cancer but I do have a question for a veterninary professional that I would like answered if at all possible. Please see below.
My cat, about 12 years old, is being treated for hyperthyroid, the medicine being used is Mehimazole tablets 5mg. At first she was given 1 tablet am and 1 tablet pm, when her blood work was done to determine her levels later - her thryoid function was now too low so the dosage was change. New dosage was 1/2 tablet am and 1/2 tablet pm she stayed on this medication about 3 months. She recently was rechecked and her thyroid level had come up some but it was still too low. The doctor first told me to increase her dosage to 1 tablet am and 1 tablet pm when I questioned this he changed it to 1 tablet am and 1/2 tablet pm then he thought about it and changed it to 1/2 tablet am (said he got the cat and dog treatment mixed up) He finally told me the dosage was to be dropped down to 1/2 tablet am only. I am really confussed - is my cat on the correct dosage or should I thinki about changing to another doctor? Any and all suggestions and advice will be greatly appreciated.
Please email me at cmfrost68@verizon.net
July 26, 2017
4 Recommendations
Methimazole is used to reduce the level of thyroid hormone in the body, the higher the dosage the more suppression of hormone production; meaning that if a cat is being treated with methimazole and the thyroid hormone level is too low, a reduction in dosage will (in theory) increase the level of circulating thyroid hormone. It is possible that your Veterinarian made a genuine mistake, as we are all humans after all. There is no real “correct dosage” as a trial and error “sweet spot” needs to be found to keep the thyroid hormone within physiological range, which is common in these types of conditions. Regular monitoring will show if you are on the right path. Regards Dr Callum Turner DVM
July 26, 2017
If a cat has thyroid cancer would the levels initially respond to methimazole? My cat has been on it for 4 months, levels came back to normal. We caught it early but he is not gaining any weight back which is concerning to me.
July 26, 2017
Elaine T.
Thanks so much to Dr. Callum Turner for taking the time to answer my questions about Susie. His reply help to make me feel better about the situation. THANK YOU, Dr. Turner.
July 26, 2017
Susie's Owner
My 16 year old cat was treated with Methimazole instead of the radioactive treatment for his thyroid several years ago,was declared "cured" after about a month of treatment, and has been on 5 mg twice daily ever since--the vet said that he would need to take it the rest of his life. We have not tested him periodically to check this as suggested here. Now he has cancerous cells in his thyroid, and they've basically given me no hope for him, as he is also diabetic, and wouldn't survive surgery. If I were to increase the dose of the methimazole, would that be a treatment that could address the cancer cells? I'm really in need of a 2nd opinion. Thank you.
Sept. 6, 2017
Sophi F.
Adding methimazole will only reduce thyroid output.My 16 year old male cat is hyperthroid and must take that all his life. Methimozole is not a treatment for cancer. A full, complete body detox is possible but expensive and only one in a hundred vets are equiped fot it. Vitamine B17 & selenium are two of the ingredients in the treatment for cancer in animals and Humans. B17 capsules must be taken apart and sprinkled on cat's favorite food. The cause of cat's cancer is clogged lymphnodes around the thyroid area, or any other area where cancer raises it's ugly head. No clean oxygenated blood can get in and expired cells can't get out This will slow the growth of cancer High Alkyline water of, as close to 8 as one can get, is very highly recommended. You can put a high alkyline water stick(google it) can be dropped into a quart of water and left in it. They last about 500 quarts of water and are inexpensive. We have two of em. That water is good for us too...Good luck and let the force be with y'all.
July 16, 2018
George
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tabby
Tabatha
19 Years
0 found this helpful
0 found this helpful
My pet has the following symptoms:
Weight Loss, Vomiting,
Our furry baby is 19 years 10 months and I’ve had her since she was 6 weeks old. She was diagnosed with a tumour back in Feb 2019, after bloods, X-ray and full body MRI scan; with both our vet and a specialist veterinarian practice. She was prescribed thyroid meds via syringe. We started giving her the meds straight away, but she stopped eating. We decided to take her off the meds after about 6 weeks, as her appetite was non-existant, and she became uninterested and lethargic. After a few days she picked up and started eating again. She put on a few ounces and spent most days in the garden, in the sunshine. As winter progressed she seemed to have malaise, sicking up her food etc, so we took her back to the vet (she has been back a couple of times but we kept visits limited as it stresses her too much), and we were told the thyroid tumour had grown. She was given a steroid and has been having one every month, for the past 3 months. She’s 2/3 of her original (slightly over weight) body weight, is sick occasionally. I’m glad she was portly as it’s helped her last this long. The hardest part is when she purrs if seems to aggravate the tumour site; it’s so cruel. She has a loud purr and has airways been very vocal. She’s still with us, each day is a blessing. We regularly change her cat food so she never has the same thing twice in a week. She has cat milk, water and hard, and soft cat food, human food (cooked fish and meats), munchies soaked in water. I’m sure this variety and treating the meals like a tapas, has kept her here longer. She’s not in pain (we’ve been told) and uses her tray for both business. She cleans her paws, face and we tentatively brush her body (trying not to encourage her purrs). That’s kept her coat knot free and shiny. What the future holds is unknown, but she probably won’t make her 20th birthday. My advice is quality over quantity, if you can afford to treat your cat/kitten to the best food you can afford, vary the diet if they go off food, smaller portions with variety. It’s worked for us. (We’ve always kept her diet varied).
Thyroid Cancer Average Cost
From 520 quotes ranging from $3,000 - $8,000
Average Cost
$6,000
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