A large abdominal mass may be lymphoma/LSA, but one can not make that
diagnosis without additional tests (ie bloodwork showing the abnormal
lymphocytes, biopsy, fine needle aspirate, lymph node removal and
histopath, etc).  The folks at the vet school at MSU should be able to
help you and your ferret.  Bloodwork and an ultasound guided aspirate may
be the next step to further work up that mass.
 
Hope that helps,
Jerry Murray, DVM
[Posted in FML issue 3482]