I've seen both and from my experience it is common in ferrets.  Dancer was
a late altered rescued breeder - she died of cancer, the Fredonia ferrets
were all late alters and many died of insulinoma, my very first ferret and
offspring were late alters and died of insulinoma (I didn't know till Nikki
was 4 and by then he'd already fathered).
 
In late and early alters I've seen - cardiomyopathy, lymphosarcoma,
insulinoma, and adrenal as well as other ailments.
 
I would guess that unless ferrets are being brought in from other countries
and being bred here, the groups of ferrets currently in the US may have
come from the same lines.  Of course there are two sides and those brought
in may bring other ailments with them that may not surface for years.
 
The Denmarks that came over a few years ago seemed healthy, but Possum was
recently diagnosed with insulinoma, our Mugsy died at 10 months of juvenile
lymphosarcoma and was Canadian as was Sharp-toothe who died of colon
cancer.
 
Years ago we didn't hear as much about cancers but back then not many
people took their ferrets to a vet when he/she was ailing.
 
Of course this is just my observations through the years and my opinion
will differ from others.
 
Hugs. tle
Troy Lynn Eckart
Ferret Family Services
http://www-personal.ksu.edu/~sprite/ffs.html
http://www.geocities.com/Petsburgh/Haven/5481/
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[Posted in FML issue 3252]