Hi X,
 
It sounds like you describing a perianal gland adenocarcinoma in your
ferret.  These are bad news.  There was an article in the April 2001 issue
of the vet magazine Compendium on Continuing Education that talked about
treatment of this type of cancer.  They used surgery and radiation therapy
to manage it.  Chemotherapy is also another option.  Sorry I do not know
about using angiogensis inhibitors in ferrets, but your vet can consult
with a vet school or other cancer specialists to see if that would be
useful.
 
Hope that helps,
Jerry Murray, DVM
[Posted in FML issue 3470]