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Cat Radiation: Full Course vs Palliative Course
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elizabeth_1 posted:
My 5-year-old cat had a small, hard lump removed from the top of his head on 12/18. He had the lump since he was around 9 months old, and it had slowly grown until it was around 5 mm in diameter (about the size of a small pea). Pathology report said that it's a fibrosarcoma with no mitotic activity and clean margins. My vet informed me that surgery for these types of tumors is usually very aggressive and involves amputation if possible, and so since they couldn't take super-huge margins on his head, I should look into radiation in order to prevent or delay recurrence.

The radiation oncologist at the local vet hospital isn't back until next Tuesday. In the meantime, I've been learning about veterinary radiation, and it looks like a full course would involve sedating my cat for approximately 18 separate treatments (until 50Gy is received). My cat HATES going to the vet, and in fact he did not eat or drink at all during the three days he stayed at my vet for his surgery. I think that the anesthesia and stress would have a very bad effect on his immune system, and thus his ability to fight off any remaining cancer cells. (I've been interested in learning about surgery-induced metastasis; anesthesia's effect on the immune system is believed to contribute to the rapid metastasis that is sometimes observed shortly after removal of a primary tumor).

I was wondering if a palliative course (3 treatments, lower total dose--maybe 24Gy) could be more effective at destroying any residual cancer cells, since my cat wouldn't be nearly as stressed undergoing 3 treatments spaced a week apart, as opposed to a treatment every day.

I am interested in hearing about cats who have received full or palliative courses of radiation, especially as an adjuvant therapy after surgical removal of a primary tumor. Do you think the benefits of the radiation outweighed the stress that the cats endured?

What about the risk of new fibrosarcomas developing as a result of the radiation?

What about long term effects, like cataracts, necrosis of bone or other tissue, loss of teeth, etc. (probably more of an issue for cats who need head radiation, like mine).
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elizabeth_1 responded:
Hopeful update:

My vet called yesterday and said she spoke with both the pathologist who biopsied my cat's tumor and a veterinary oncologist. The pathologist said that the tumor was so low grade that he had trouble deciding if it should be classified as a fibroma (benign tumor) or a fibrosarcoma. After consulting with another pathologist he decided that the tissue was just "cellular" enough to classify as fibrosarcoma.

Based on the low grade of the tumor, and the fact that the margins in the examined portions were clean, the oncologist suspects that my cat is probably "cured" and does not need radiation at this time. We will just have to monitor his head closely over the next 1-2 years to make sure it doesn't come back.

For a small price ($70), the pathologist can do a more thorough check of the margins of my cat's tumor. My vet didn't know if this meant he would recheck the existing three slices (two parallel and one perpendicular to long axis), or if he was going to prepare some additional slices and look at those. Since I had been preparing to spend a few thousand dollars on radiation, I told my vet that I would be willing to spend significantly more than $70 if they could do a super-thorough check of the margins. She is going to talk with the pathologist on Monday to see what different margin-checking procedures they offer, and how much they cost.

So, if the pathologist finds no "dirty" margins during his second check, I will not pursue radiation at this time. However, I am still interested in learning about how cats fare with radiation treatments, because it still might be possible for his tumor to come back, despite the clean margins and low grade.
 
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AMERICAN VETERINARY MEDICAL ASSOCIATION
Sandy Willis, DVM, DACVIM replied to elizabeth_1's response:
Hi,

Sorry for the delay. You write some excellent questions and many that an oncologist like the one you consulted with would be the best to answer. I am a small animal internist and I have seen cats and dogs treated every week with general anesthesia for radiation therapy and they have fared really well. Some cancer like the fibrosarcoma don't do well with chemotherapy.
But your questions are so important to ask your veterinarian and the oncologist. The question of benefits of treatment vrs stress is very important. Cats and dogs live so much shorter than we do that we really try to minimize stress due to anesthesia, visits, chemotherapy, etc but if we can give our pets remission from cancer or even cure AND a good quality of life (and owners can afford the treatment) than that is the goal. There are so many options and your family veterinarian and specialist are always willing to work with you. Dr. Sandy
 
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elizabeth_1 replied to Sandy Willis, DVM, DACVIM's response:
Dr. Sandy,

Thanks for the response. My main concern is how stressed/unhappy my cat gets when at the vet or around strangers. During his stay at the vet after his surgery he did not eat or drink at all.

However, the oncologist thinks that his tumor was so low-grade (BARELY classified as fibrosarcoma; pathologist had trouble deciding between fibroma and fibrosarcoma) that he might not need radiation at all. They are doing a more thorough check of the margins, and I should get the results next week. If the re-check finds any dirty margins, then I'll see what the oncologist recommends.
 
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elizabeth_1 replied to elizabeth_1's response:
The more thorough margin check did find neoplastic cells extending into the margin in one of the additional four slices that the oncologist checked. He has an appointment with a radiation oncologist to discuss what to do next. I spoke with her over the phone today and she said his treatment could involve re-resection, radiation, or both. They are going to x-ray his lungs also to make sure it hasn't metastasized; if it has, there is probably no point putting him through surgery and radiation. While fibrosarcomas aren't highly metastatic, the oncologist said she has seen cases where a low-grade fibrosarcoma has metastasized. I am also going to bring the pathology reports, plus photos of his tumor before surgery and his incision after surgery (the oncologist had asked how long the incision was).
 
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elizabeth_1 replied to elizabeth_1's response:
  • **oops; first sentence should say, "...in one of the additional four slices that the PATHOLOGIST checked," not oncologist.
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    elizabeth_1 replied to elizabeth_1's response:
    UPDATE:

    It's been 4 1/2 months since his tumor was removed. It has not returned yet, though I think the mean tumor-free interval for for low grade fibrosarcoma in cats is something like 14 months (based on a small study) so I wouldn't necessarily expect it to be back yet.


    I met with a radiation oncologist and surgeon at a veterinary oncology center in January. Chest x-ray was clear. The surgeon said that re-resection is not recommended because getting the 2 cm margins would require removing the top of skull and replacing with a prosthesis, and at this point his cancer is not threatening/aggressive enough to do that type surgery.

    Therefore, the two approaches to consider are radiation and the "wait and see" approach. According to the surgeon, in dogs, incompletely excised low grade fibrosarcomas with no adjuvant radiation have a recurrence rate of 7-12%. According to the oncologist, recurrence rate is 10% WITH adjuvant radiation. Those numbers suggest that adjuvant radiation doesn't help much with low grade fibrosarcoma in dogs. Radiation DOES decrease recurrence of low-grade fibrosarcoma in humans, but it does not increase survival or reduce metastasis, and it actually increases morbidity. There are no large studies of low grade fibrosarcoma in cats.

    The oncologist said that her team is good enough to spare my cat's sensitive tissues (eyes and brain). I forgot to ask about salivary glands. There is a 5% risk of radiation-induced cancer later in life (usually bone sarcoma). The radiation would cost $6,000-$7,000, depending on the type used (intensity modulated radiotherapy, or electron beam), which they would determine after CT scan of the head.


    The radiation oncologist said that there is no "perfect" recommendation due to the lack of research on low grade fibrosarcoma in cats. However, she said if it were her cat, she would do radiation.

    I have been spinning my wheels making this decision. Radiation therapy has a disproportionate effect on fast-growing, poorly differentiated cells, which is why it works so well against cancer, and does not work well against benign cells (however, radiosurgery can be used to destroy small benign tumors). However, my cat's tumor was extremely slow growing (zero mitotic activity in examined slices after removal), and also well-differentiated--in fact, the pathologist had trouble deciding if it was benign or malignant--so if the radiation has an equal effect on his head's healthy cells and the residual cancer cells, I don't see how they could be sure to destroy all of the cancer cells without destroying all of the healthy cells as well (i.e., frying off the top of his head).

    I found an oncologist a few hours away who I think might be able to answer my questions (she has a background in radiation biology), so I need to make an appointment and get down there.

    In the meantime, I'm continuing to feed my cat his lower carb food, and I stopped giving him starchy treats (green beans, corn, etc,). Once every two weeks I palpate his head to make sure the tumor has not returned. They also recommended getting a chest x-ray every few months for the next couple of years, but this cancer it not highly metastatic so I will probably do it once every 6 months, just to minimize his stress. And just to be on the super-duper safe side, I'm going to skip his Frontline for the next couple of years, unless I find fleas on him (just to be clear, I don't blame Frontline for his tumor; his tumor first appeared before I had ever used any flea treatment on him).
     
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    elizabeth_1 replied to elizabeth_1's response:
    UPDATE: It's been nearly seven months since my cat's fibrosarcoma was removed, and it hasn't recurred yet. I palpate the top of his head once every two weeks. He had a chest x-ray yesterday (to check for metastases) and it was clear. The vet also palpated his head and didn't feel anything.

    I think I'll start to feel more afraid around the one year mark...and if he makes it to two years I'll start to feel relieved. Given his age and excellent health, it's a little strange to have that awareness that he might not have much time left, but I'm getting used to it.

    See my original post/pictures of tumor here: http://forums.webmd.com/3/pet-health-exchange/forum/5445/5


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