Tracy Tunnison noted a few issues back that she felt she had to breed a jill
with possible congenital cataracts because the jill was in heat, too far
gone (into heat, I assume) to spay and didn't want to subject the ferret to
"that injection as it has carcinogens."
 
I won't comment on when a jill in heat is too far along to spay or not.  My
knowledge of obstetrics is limited to female humans, who don't go into
"heat" (I know parents with teenage daughters who would argue that last
point, but I'm going by what the textbooks say.) However, I may be able to
clear up some misunderstanding about hormone injections and cancer.
Actually, I'll probably confuse people even more, but here goes anyway... ;)
 
Whether any hormone can be thought of as directly carcinogenic is highly
debatable.  Hormones are simply messengers, albeit, often powerful ones,
that tell various cells in the body of an adult to turn genes on or off, or
perform different tasks.  Where hormones and cancer interact occurs when an
animal has a tumor that is responsive to a particular hormone.  Reproductive
cancers are notorious for this.  Breast and endometrial cancers can
proliferate much faster in the presence of estrogens, and prostatic cancer
can become more aggressive and grow faster in the presence of
dihydrotestosterone (DHT).  These hormones *do not cause* the cancer; they
do accelerate it.  Eliminating these hormones often assists anticancer
treatments or keeps tumors from growing as quickly.  In the case of breast
cancer, some tumors do not carry estrogen receptors and these tumors are
*more* often fatal because the tumors have one less weak spot to attack.
 
In the womb, however, hormones can possess vastly different properties.
Some hormones that have one function in adults may do something entirely
different in an embryo or fetus, or may do several different things
depending on the point of gestation or where in the developing baby the
hormone is produced.  In this setting, hormones orchestrate the development
of organs or limbs and an imbalance of a hormone during this stage can have
major developmental consequences.  Hormonal upsets in the embryo or fetus
rarely result in cancer of the fetus or newborn, but can result in all sorts
of developmental defects too complex to discuss here.
 
To bring a ferret out of estrus, a hormone shot is used that tricks the body
into thinking that the animal has gotten pregnant.  The whole purpose of
estrus is to prepare for pregnancy, anyway.  The hormones used are either
synthetic or natural forms of female hormones, usually progesterone.  (I
*think*...Any vets please correct me is progesterone is not the typical
injection in non-humans.) This is usually a one-time deal.  The body gets a
hit of what it's been hoping to see in the bloodstream and--usually--the
animal comes out of estrus.
Does this increase the risk for cancer?  The answer is a conditional "no."
If the jill happened to have an undetected hormone-sensitive tumor at the
time of the injection, the shot *might* increase the rate at which that
cancer grew or spread, but only transiently.  (It was only one shot,
remember.) So, in that rare instance, it's possible that the cancer might
show up a few days earlier than it might have otherwise, but the shot could
not have *caused* the cancer.  It's more likely that such a transient
stimulus wouldn't have any affect at all.  In contrast, bringing a litter to
term, giving birth and nursing can much more traumatic, especially one that
may have congenital defects which may include other unseen health problems
that might complicate a pregnancy.  I don't know the rate of complications
in ferrets or other non-humans, but before the advent of antibiotics,
C-sections and other current obstetric techniques, one in five women used to
die in childbirth.  Pretty scary odds, eh?
 
Occasionally, a jill cannot be taken out of estrus by injection.  In that
case, the vet and/or owner would have to make a judgment about whether the
jill should be spayed or mated.  That's out of my expertise.
 
The application or inhibition of hormones can be lifesaving.  The problems
usually arise when hormone levels are out of balance in utero, in the
presence of a hormone-sensitive cancer or when an imbalance persists over a
long time.  By themselves, however, hormones don't cause cancer and the
brief exposure endured with a single injection should be even less
worrisome.
 
This issue is *way* more complicated and subtle than I have the room for
here.  (Thank you BIG for the length limit!) I can hardly wait until another
major infectious disease thread resurfaces!  Uff da!
--Jeff Johnston ([log in to unmask])
 
[Moderator's note: The injection used for ferrets is hCG - Human chorionic
gonadotropin.  BIG]
[Posted in FML issue 1659]