Spenalomegaly in ferrets is usually NOT malignant.  In this it is like
adrenal growths.  Surgery to remove the spleen is typically without
negative effects (also similar to adrenal growths) and the ferrets
usually improve greatly after (a third similarity to adrenal growths).
Imagine if you were carrying around a 40# spleen.  Now imagine how much
better you would feel without it.  Ferrets don't tend to have negative
consequences of such surgery.  When a person is leery of trying surgery
straight out, it sometimes can pay to try 4 or more weeks of Biaxin and
Amoxi since most enlarged spleens in ferrets are from slowly smoldering
infections and this combo hits several including helicobacter which is
very common.  That depends on how great the risk of rupture is.  Your vet
will gently pat/massage/move the spleen during surgery before removal to
up the blood levels in the body first.  If the margins are not smooth
that increases the chances of it not being a benign problem, but benign
spenalomegaly in older ferrets is very common.  Meltie had 3 and 1/2
mostly excellent years in her after removal of a benign spleen and a
malignant adrenal at age 5 years.
 
[P.S.]
Be SURE to have the spleen sent out for pathology and that the proper
procedures (such as no freezing which bursts cells and ruins samples)
are used so that the pathologist can check it carefully.
[Posted in FML issue 3925]