The issue of whether ethoxyquin, an antioxidant added to pet food to prevent
spoilage, causes cancer has come up on the list recently.
 
I searched MEDLINE for abstracts of animal studies involving neoplasms and
ethoxyquin.  There were a couple of dog studies, but most of the studies
involved rats, mice, and hamsters.  Most of these studies looked at the
ethoxyquin's inhibitory or facilitating effects on the development of
neoplasms caused by other chemicals.  I did not see any studies where
ethoxyquin was studied as the primary causative agent.
 
Abstracting from these abstracts (a dangerous thing to do), it seems that
ethoxyquin does promote gastric, renal, and bladder cancers in rodents
exposed to carcinogens.  One dog study also seemed to conclude that
ethoxyquin enhances the effect of carcinogens in the development of thyroid
cancer.  Some rodent studies looked at ethoxyquin's protective effects
against chemically-induced liver and lung cancers.
 
I'm not sure what we can conclude from this.  I conducted a very quick
search on a database dedicated to human medicine, not a veterinary database
or a directory of funded research.  That I didn't see more dog studies or
any cat or ferret studies doesn't mean there aren't any.  Also, although the
studies I saw only looked at ethoxyquin as a secondary, not a primary, agent
in cancer development doesn't mean that there aren't studies on ethoxyquin
as a primary agent.
 
I do want to point out that different chemicals have different effects on
different tissues, and different effects among species.  That ethoxyquin
enahances the carcinogenic effects of other chemicals on rat bladders does
not mean that it will cause adrenal disease in ferrets.  That ethoxyquin
seems to protect against lung cancer in hamsters does not mean that smokers
should start eating Iams Kitten food.
 
Also, one study finding a positive correlation may be contradicted by
another study finding no correlation.
 
We need to keep in mind that preservatives, like ethoxyquin, are added for a
reason.  Spoilage and degradation of vitamins in food can cause or
contribute to disease, including cancers.  If you choose a food that does
not have added preservatives, it is especially critical either to buy it in
small quantities or to keep the bulk of it refrigerated or frozen in
air-tight containers.
 
-- Lee
[Posted in FML issue 2121]