Current Thinking on Feline Injection Site Sarcomas

Presenter – Professor David J. Argyle, Recognised Specialist in Veterinary Oncology, William Dick Professor of Clinical Studies, Royal (Dick) School of Veterinary Studies, The University of Edinburgh Hospital for Small Animals

I have been fortunate enough never to have diagnosed a case of Feline Injection Site Sarcomas (FISS) but after a well spent hour listening to ‘The Webinar Vet’s’ Thursday session, Professor Argyle showed that this is a problem we are all likely to encounter at some point in our careers.

FISS is a complex disease with a poorly understood pathogenesis. It is thought to be associated with post injection inflammation and can occur within a relatively short time frame after injection, with a latency period of anywhere between two months and two years. Despite only a statistical link with FeLV and Rabies vaccination, FISS is considered to be related to any injection which may cause inflammation. Worryingly, Professor Argyle showed us data demonstrating that the incidence of FISS has rapidly increased in the past 10 years although pharmacovigilence data supplied by the VMD shows the incidence remains low.

So what do we do if we find a post vaccination lump? Reassuringly, Professor Argyle states that these occur relatively frequently and most will resolve in 2-3 months. Most vaccine associated sarcomas will not occur in cats before three months following vaccination. Professor Argyle’s advice is to biopsy a post vaccination lump if it has grown more that 2cms within three months or if the lump is still present at three months.

Achieving a diagnosis by cytology alone can be difficult so Professor Argyle suggests always performing an incisional biopsy. Although only 20% of FISS metastasize it is also always worth performing full bloods, urinalysis and thoracic x-rays. However he was very keen to stress that a key factor in improving the outcome of these cases is to always go one step further and perform MRI or CT. This allows for the extent of tumour invasion into deeper tissues to be evaluated.

Treatment of FISS is very difficult with a cure rate of only 10%. Professor Argyle reported his greatest success rate when combining radiation with radical surgical excision. Radiotherapy is performed prior to surgery with the goal of ‘sterilising’ the margins. Surgery is then carried out taking a margin of at least 3-5cms of macroscopically normal tissue and at least 1 fascial plane beneath the tumour. My assumption that these cases were usually best served by referral was justified by hearing that the disease-free interval is increased from 10 months to 16 months when surgery is performed by a board certified surgeon.

It was clear from Professor Argyle’s veterinary webinar that FISS is not a disease that any of us want to encounter, but on a more positive note there are some new therapies on the horizon which may help with its treatment. It may also be time to consider altering my usual inter scapular injection site as recommended by Professor Argyle so excision of these prolific masses is made just a little easier.

The Stethoscope (MRCVS)

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