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LYMPHOSARCOMA IN SIAMESE CATS - A NEW BETTE NOIRE?
By NICK MAYS, Chief Reporter

WHEN TOP Siamese breeder/exhibitor Christina Knowlson of Drestothril Siamese discovered a number of cases of Lymphosarcoma - specifically Thymic Lymphoma - in kittens bred out of her two year-old Seal tabby Point Siamese , Imperial Grand Champion Daktari (the first Imperial Grand Champion Siamese), she was horrified.

In just six months, four of Daktari’s progeny – by different queens – had developed Lypmhosarcoma and had been put to sleep to prevent their suffering. Not surprisingly, she was desperate to know what to do. It looked as though Lymphosarcoma in Siamese cats was set to become the breed’s own bette noire, like PKD had been in Persian lines.

The next few months were a steep learning curve for Christina, during which she was helped and supported by several Siamese breeders who had either experienced the disease or simply wanted to help for the good of the breed. However, there is some glimmer of hope: Research and DNA testing by Bucaal Swab could possibly uncover a hereditary gene.

Then breeders would be able to test their cats and keep a register of affected cats, so those carrying the gene (if there is one) would not be bred from, as was the case with PKD testing previously.

But is Thymic Lymphoma necessarily a death sentence?

Case Histories
In January 2006 Christina’s first case of Thymic Lymphoma - Cancer of the Thymus - was diagnosed in a Seal Tabby Point kitten, named Delightme aged six months the result of Daktari’s first mating to Drestothril Daddys Girl.…

The next case was a Seal Point female kitten sired by Daktari to his first outside queen, who was brought into stud by a close friend of Christina’s. This kitten died from the same cancer at 7 months of age. She had been living with her new owners at the time, and was a much-loved family pet.

Soon after this, the third case came to light in a kitten born to another dam, a queen not of Christina’s breeding line, but one that she had brought in to put to Daktari. This kitten was an attractive Tabby point female aged 7 months who was also put to sleep to prevent suffering after the swift onset of the disease.

The fourth case was the sister of Delightme, a Seal point named Twinkle, who was seven weeks pregnant when she developed the cancer. Her owner, a prominent Siamese judge was devastated. Twinkle was part of her family and was only 15 months of age. Twinkle died, her cancer was too far advanced for treatment to be effective.

The third and fourth cases occurred this summer just a week apart. Christina was faced with a terrible dilemma and had to take a decision on what to do for the best.

Christina says: “There came a time when, as a breeder commited to the welfare of Siamese, I had to take stock of the situation. Here were four cases of Lymphoma of the thymus, all sired by Daktari, who is a particularly good example of the breed, and three different queens were involved.

“It doesn’t take much intelligence to think there could be a possible hereditary factor involved in the high incidence of Lymphosarcoma.

My vet - who is also my friend’s vet - had vaccinated all four kittens when they were younger and was very much aware of my situation, as he receives many pet cancer referrals to his clinic. He suggested I wrote about the problem if I wanted research into the cancer.

I decided to raise awareness of the problem in the hope that with the help of other breeders and experts, the disease could be eliminated from the breed.”


Help and Advice
The upshot of this decision was that Christina wrote an open letter to other fanciers, which she sent to other Siamese breeders, clubs and BACS. Her letter was published in OUR CATS some weeks ago and brought forward several responses from concerned breeders, some of whom had experienced the problem .

Since her letter was printed in Viewpoint things have progressed over the following weeks. The Feline Advisory Bureau had been most helpful, with Claire Bessant offering her help, whilst Julia May passed on a great deal of information on DNA testing for such conditions, having been instrumental in the Persian PKD testing a few years ago.


Imperial Grand Champion Drestothril Daktari, owned and bred by Christina Knowlson

Christina’s vet Ron Lowe introduced her to Dr Leslie Lyons, a professor working in the Department of Population Health and Reproduction at the School of Veterinary Medicine in the University of California.

Professor Lyons is researching DNA of affected cats, as this cancer has been recognised as having a familial link and is prepared to receive DNA samples from cats in the UK. If a specific cancer-causing gene can be isolated, chances of treating affected cats and bloodlines will be dramatically improved.

Studies by the Animal Health Trust in Newmarket, Suffolk has shown that there is an increased incidence of Lymphosarcoma in families of Siamese and Orientals. On a very positive note, they have treated a considerable number of Siamese successfully; Thymic Cancer does not have to be a death sentence.

Christina adds: “My first thought was to neuter Daktari. I have been loath to do this. Who knows what the future holds with research into this cancer?

I hope eventually to breed with Daktari again, but until we get more information, he will not be entertaining the ladies. I am fortunate in having other boys at stud that I can use. If the gene can be isolated in various bloodlines, then I and other breeders will know not to use those lines, whilst any affected cats can immediately receive the necessary and correct treatment.

“We may find there are other factors involved with this particular cancer. Could it be pre-empted by infection - or vaccination – or even by environmental factors? I feel it is a very complex mode of inheritance involved dating back 30 or more years and certainly not to any one particular stud.
“I wish I could educate the breeders who blame individual cats.

The simple fact is that Siamese as a breed have a tiny gene pool .We owe it to everyone involved, the cats and their owners, to do all we can to extend the cats’ longevity and prevent this cancer from spreading if at all possible. I can only urge as many Siamese breeders as possible to get their cats DNA tested, because not only will it benefit their own cats, it will benefit the breed.”

Words Of Warning
More recently, two further cases have come to light. The fifth case was a Chocolate male, a littermate to the friend’s kitten who had died earlier in the year.

He was diagnosed a few weeks ago and is now being treated - so far successfully - with chemotherapy by a local vet.


Drestothril Delovely, the first of Christina’s kittens sired by Drestothril Daktaro to develop Thymic Lymphoma.

Sadly, the sixth case, another kitten was not so lucky and he has since died.

Christina sums up, with words of hope and also of warning: “I’m sure the gene can be isolated, it just needs proper investigation by using DNA samples - as many as possible.

Lymphosarcoma can be treated successfully by chemotherapy - I have heard from other Siamese breeders and owners who have had their cats treated in this way, It isn’t necessarily a death sentence - but it will be if it isn’t taken seriously. Quite simply and quite truthfully, it could be your cat next!”


Open Letter from Christina Knowlson
There comes a time when one has to stop and take stock. Alarm bells rang when the second kitten sired by Daktari developed cancer. Fear and panic when the third and fourth kittens developed the same cancer. I had to tell everyone.

OUR CATS published my open letter in their Viewpoint and support came flooding in. Top Siamese Breeders, Judges and Vets wrote rang or emailed me. In the darkest time, when case five and then case six just this week developed, you have supported me with sympathy and information.
In particular I would like to thank Moya and Stuart, Alice, Marion and Gina who kept me smiling, Anne who passed the letter to Jackie, who in turn introduced me to her friend, breeders Pat, Jane and Dorothy who gave me support, help and information.

Thanks too to everyone who took the time to contact me. There were so many; Sarah, Pennie, Pippa, Lynne, Frances, Anna and Neil… Jean, Janet, Di and Jenny… Amanda, Maureen, Celia, Lisa, Jenny, Carole, Paul, June and her friend in the States, Liz, Joan, Richard, Mark, Barbara for the talk at the Forum, Claire Bessant, Julia May and my vet Ron Lowe.

Thank you all so much.

Christina Knowlson


Thymic lymphoma

Information from Julia M. May, Feline Advisory Bureau
Thymic Lymphoma is a cancer which affects the thymus and mediastinal lymph node in the cat’s chest. It is generally seen in young cats.


It appears to be particularly common in Siamese and Orientals compared to other breeds or to non-pedigree cats. This is usually described as a ‘familial’ tendency, which means that there is a high risk, but no absolute proof, that there is a genetic component to the disease.

This is NOT a new disease. Decades ago it was common in Siamese and Orientals, with rumours about particular cats in the ancestry. This situation has not changed, but some other things have. In those days when FeLV was common, even when it occurred in cats which tested negative, from households which were negative, rumours went round that the tests were incorrect or the breeder/owner careless.

Now that testing is routine and FeLV vaccination is common it is clear that thymic lymphoma can crop up in households of cats which have been FeLV negative for generations and with the most careful of owners.

The other thing that has changed is that the feline genome has been studied and various genes are being identified, so that DNA testing for some problem genes is now in existence.


Unfortunately, no specific gene has yet been isolated for thymic lymphoma. So far it remains ‘familial’ because nobody can be sure if the disease is caused solely by one gene, dominant or recessive, by one gene in combination with others, or by a gene (or more) in combination with some other factor.

However, Dr Leslie Lyons, at the University of California, Davis, is working to try to find a specific gene, if one exists. This work is expensive and laborious and requires a great deal of help from cat owners.

DNA swabs are required from affected cats and from their parents, siblings and other cats in the household, together with pedigrees to show the relationship between the cats. It is a matter of hoping to find something which occurs in the affected cats, but not in the unaffected ones.
Since this work is already under way in the US, there is little point in trying to raise the vast amounts of money which would be required to set up parallel research in the UK. However, funding at UC Davis is needed urgently in order to continue the research.

How you can help
• The sample required is a cheek swab, not a blood sample

• You can take this yourself - it does not have to be taken by your vet

• Your cat does not need to be microchipped - there is no feedback at this stage

• The ‘swabs’ are sterile cotton swabs or cytology brushes in separate sealable paper containers

• The samples are easy to take - you have to remember to wait at least 30 minutes after the cat has eaten before swabbing its mouth - and you have to remember NOT to blow on the swab to dry it before sealing it back into its container!

• In addition to the swabs and details of the cats from which they have been taken you will need to enclose proof that the affected cat(s) did indeed have thymic lymphoma and not another form of cancer or other thoracic problem: this may be a copy of the X-ray/scan or case notes from your vet.

• There is no need to worry about confidentiality - there are no results at this stage, just ongoing research


The future
Once a gene, hopefully, has been isolated it will then be possible to test cats for that gene.
At present the Abyssinians and Somalis are at this stage with the (recessive) gene which causes pyruvate kinase deficiency: they are raising the money required to set up a testing programme to find out how prevalent the gene is in the UK.

After that has been established they may go on to set up a register to record positive carriers and negative cats.

FAB has already set up a register which records PKD (polycystic kidney disease) in Persians and Exotics and produces certificates for negative cats: this was originally determined by ultrasound scans, but since the gene was isolated, at UC Davis, the test is much simpler and can be used in kittens.

Other things

Thymic lymphoma is not the only cancer which can affect our breeds - for instance mammary tumours also seem to be rather common in Siamese - but it is the particular cancer which we would like to concentrate on at present because there is a good chance that it will prove to involve a hereditary factor.

If this proves to be the case, and the gene can be identified, we might be able to reduce the heartache of losing a young and otherwise healthy cat or of deciding whether or not that cat is a suitable candidate for chemotherapy after considering all the practical and financial implications.

Until the genetic components of thymic lymphoma are understood breeders should not neuter cats just because they might be implicated - this could lead to a reduction in the available gene pool without reducing the incidence of the disease.

Obviously, a cat which actually has thymic lymphoma, or has produced many affected kittens, is more likely to pass on any tendency to develop the disease, so breeding from such a cat is not advisable, but at present we have no way of determining whether parents or siblings are affected.


If a gene is isolated in the future any such decisions can then be made on a scientific basis.

* Contact Dr Leslie Lyons at felinegenome@ucdavis.edu for swabs (if you cannot get any here) and forms and information on swabbing at:

http://faculty.vetmed.ucdavis.edu/Faculty/lalyons/Sites /Protocolsframe.html
Send swabs etc and donations to: Department of Population Health & Reproduction, School of Veterinary Medicine, University of California, Davis, Davis, CA 95616, USA