There are multiple pieces of info on the misuse of the term "cancer";
here's one which combines the marvelous post of a veterinary pathologist
who is a highly respected ferret expert (Dr. Bruce Williams) and some
dictionary definitions from veterinary/ medical dictionaries.  For
example, message 6510 (There ARE others with more info):
 
At 8:59 AM +0000 8/20/01, Dr. Bruce Williams wrote:
 
BEGIN QUOTE
The thread on this is pretty good, and both Sukie and Stephanie have very
valid points.  The terminology of neoplasms can be confusing, and I'm
sure even vets can be confused from time to time.  The proper term for
what you are talking about is neoplasm (or literally "new growth).  For
one reason or another, a clone of cells begins to grow uninhibited by
normal substances or mechanisms.  The word "tumor" may be technically
correct, but it is actually non- specific - tumor is Latin for a
swelling, but it could also be an abscess, or anything else that causes
swelling - so I try to stay away from it.
 
Now this neoplasm may be benign - without the ability for cells to
detach into the bloodstream or lymph, move to another tissue, and set
up shop - or malignant (where they can do this.) The process of a
microscopic piece of a tumor moving to another organ is called
metastasis.
 
Metastasis is the hallmark of malignancy.  The worst tumors have the
propensity to go anywhere and start growing (like lymphoma).  However, we
can recognize malignant tumors even before they metastasize, often by
characteristic features seen under the microscope.
 
Adrenal carcinomas (malignant adrenal tumors) are interesting neoplasms.
Although they possess the ability to metastasize, only a small number do,
and usually only late in the course of disease.  It is likely that they
do metastasize a lot, but have trouble gaining a foothold in distant
tissues, so it takes a long time and many attempts if they ever truly
metastasize.
 
Insulinomas are generally not malignant tumors as they only very rarely
metastasize.  The presence of multiple tumors in the same organ over
time is not metastasis.  We do not understand the mechanism behind the
generation of these tumors, and when we do surgery to remove them, we
really are only treating the end point of this process, without
addressing the cause.  Thus it is really no surprise that the rate of
recurrence is about 40% within 10 months.
 
With kindest regards,
Bruce Williams, DVM
 
END QUOTE
 
Treat this as a supporting document to Bruce William's excellent post
above taken from FHL digest 348.  I especially liked his providing the
direct translation of "tumor" as "swelling", and his explanation that not
all growths which can metastasize do so readily.  These definitions are
combined ones from medical, veterinary, and biology dictionaries, but
emphases are mine and i am willing to be corrected if I blew it... (New
note in 2005 -- in the 4 years that this has run no one has disagreed
with the medical dictionary definitions and it has been read by vets,
physicians, and other experts in that time.)
 
Important Note: some more recent dictionaries don't even include the term
cancer as a valid health term any longer, and I have heard vets who won't
use it due to the widespread confusion out there, and even some vets who
won't use "tumor' due to too many assuming that any tumor is malignant.
[Posted in FML issue 4930]