September/October 2002 issue of Veterinary Surgery, G Hosgood*
Official Journal of the American College of Veterinary
Surgeons
and the European College of Veterinary Surgeons
Progression of vaccine-associated sarcoma in
a cohort of 294 cats described by a Markov process
P Kass
D T Scholl
Louisiana State University, Baton Rouge, LA
Vaccine-associated sarcoma (VAS) is an emerging problem
seen in the pet cat population. The disease typically follows a chronic course.
While studies have focused on hypothesis testing of treatment protocols by
comparing survival and recurrence times, these studies do not describe the
progression of the disease, nor provide information useful for individual
decision-making. This study applied a Markov process to a cohort of cats with
VAS to describe the progression of the disease and compare progression with
different treatments.
Data from 294 cats diagnosed with VAS from 1989-1994 at University of
California, Davis was used. Each cat's disease progression was recorded until
absorption by death or euthanasia. Recurrence was defined as local tumor
recurrence or metastasis. The times between transitions were used to obtain the
MLE of mean transition rates per month to transient states (q) and
absorbing states (u). From the inverse of the rates, the mean residence
time spent in each state was calculated.
All cats started diseased. 100 cats were alive at the end of the study, 25 had
died and 169 were euthanized. The transition rate matrix (Q) for all cats,
showed similar death rates without treatment (i.e. directly from Disease) and
Recurrence1 however, the death rate was substantially higher after Recurrence2+.
Interestingly, the euthanasia rate was highest after Recurrence1, perhaps a
result of owners rejecting further treatment and electing euthanasia. The mean
residence time for all cats was an average survival of 27.44 months. A Markov
process can be used to model the progression of feline vaccine-associated
sarcoma and may generate information that will facilitate individual
decision-making.
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