Okay, I promised to ask vet, Bruce Williams about that recent article.
Here is what he replied:
 
Pheos are extremely rare in ferrets, and the majority of these that are
diagnosed are usually poorly differentiated cortical carcinomas, instead.
You can run some tests on these neoplasms to precisely delineate a
cortical vs medullary origin (pheos are tumors of the adrenal medulla),
but unfortunately, most labs simply base the diagnosis on visual
inspection.  Early on, I got taken in by these many times.
 
However, this is not to say that the vastly more common adrenocortical
tumors are not genetically based - it has always seemed fairly obvious to
me that a neoplasm with such a high incidence in America has got to be
genetic in origin.
 
Bruce
[Posted in FML issue 3780]