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Encyclopedia of Feline Veterinary Medical Information
Fibrosarcoma - Vaccine Related
Unfortunately, cats develop vaccine related fibrosarcomas. This is a problem which has come to light in the last few years and it is one for which there is no clear consensus about the proper way to publicize and deal with it among small animal veterinarians.
To the best of my knowledge, no one knows the exact rate of occurrence of these fibrosarcomas as a result of vaccination. This is a tumor which can occur naturally, without the influence of vaccination, making it even harder to pin down any sort of specific numbers. At present, it is generally believed that these can occur as the result of any of the vaccines normally used in cats.
It is hoped that vaccines produced with recombinant gene technology may eliminate this reaction as they are possible to make without adjuvents, the irritating substances included in vaccinations in order to make the body react to them. It is also very likely that the nasally administered vaccinations will be less likely to cause this problem. These vaccines have been unpopular because they sometimes induce mild to moderate symptoms of the diseases they are meant to protect against. People didn't like that but it may be better to have a regular risk of sneezing rather than a less common, but extremely serious risk of cancer.
I suspect that many cat owners are unaware of this risk.. Most veterinarians are reluctant to tell every cat owner about the risk of fibrosarcomas and to explain the risk/benefit ratio of vaccination for each individual cat. I believe that would be the best approach to take and do discuss risk vs. benefit of vaccinations with many of my clients but not nearly all of them. It is not a good idea to abandon vaccination entirely since the disease we are attempting to protect against can be an even bigger risk to the cat but it is important to assess the risk/benefit ratio and to vaccinate only when necessary.
Without any sort of quantification of the risk of the tumors post-vaccination, I think that many vets are just sort of feeling their way through this situation and hoping that sometime soon there will be some sort of clarity. Veterinarians have always viewed vaccines as pretty benign and often had the attitude that the risk of vaccination was so small that there couldn't be a smaller risk of getting the disease. Now that we know that vaccines are not always benign, we are undergoing a painful shift in thinking -- and it is painful and difficult for many of our patients and clients as well.
It is very important to do a thorough job of removing this type tumor and all tissue surrounding it for at least 2 to 3cm in all directions, including underneath the tumor. This is a major surgery. There is some evidence that radiation therapy after surgical removal of the tumor may help prevent recurrence, if that is an available option. Despite very aggressive efforts to remove all of the tumor it is likely that 50% or so of these tumors will recur anyway. The first surgery is by far the best chance at getting it all, so it is necessary to do it right.
The bottom line is that aggressive surgical excision is the best hope for successful treatment and that even more aggressive therapy with radiation could be called for.
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Last edited 01/13/08