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Spay, Neuter, and Cancer: Revisiting
an Old Trinity
by Myrna Milani, BS, DVM
Perhaps no aspect of pet ownership in the U.S. elicits as passionately
supportive emotions as the subject of spay and neuter. In fact, this
orientation is so well established that saying anything that questions
the procedure is akin to blasphemy. However, just as women were routinely
relieved of their reproductive organs with a "La de da, you'll
never miss 'em" attitude until studies exploring the nonreproductive
effects of reproductive hormones made human physicians rethink this
position, so veterinarians and other animal-care professionals are
making tentative moves to rethink wholesale sterilization of companion
animals, too.
To understand what difference this may make in our attitudes about
the procedure, let's consider the subject of cancer. Most dog owners
have heard that spay and neuter prevent testicular and mammary (breast)
cancer: however is that the whole story relative to cancer or is there
more to it?
Obviously, if we remove a dog's testicles, there's no way he'll develop
testicular cancer. On the other hand, most dogs who develop testicular
cancer respond well to castration, so the advantages of preventive
surgery are perhaps not as great as one might expect. Although intact
(unsterilized) females have a higher incidence of mammary cancer,
the dog's weight plays an important role in the process: intact females
who are lean at one year of age have a lower incidence of the disease
compared to their chunky cohorts.
In an interesting article in the August Veterinary Practice News entitled
"Can we neuter cancer in dogs?" veterinary oncologist Kevin
Hahn opens by saying that, after reviewing studies reported over the
last 30 years, he's not sure what to recommend to his clients. Like
most veterinarians, Dr Hahn mentions the higher incidence of testicular
and mammary cancer in intact animals, but also notes that spayed females
have a 4 times greater risk of cardiac hemangiosarcomas, and neutered
males also show a significant increased risk for this cancer compared
to intact ones.
Another cancer Dr Hahn discusses that deserves mention is prostate
cancer because a lot of people erroneously believe that castration
prevents this. In reality, it does not. In fact, castrated dogs have
up to a 4 times greater risk of developing prostate cancer than intact
animals. At the same time, spayed or neutered dogs have a 1.5 to 3
times greater chance of developing bladder cancer. Because of this,
rectal examinations and abdominal palpation should always be part
of a routine veterinary physical examination.
The link between sterilization and osteosarcoma (i.e. bone cancer)
is also troubling: Spayed and neutered animals are twice as likely
to develop this cancer. Those spayed or castrated before their first
birthdays had a roughly 1 in 4 lifetime risk for osteosarcoma and
were significantly more likely to develop a tumor than intact dogs.
The article then goes on to discuss the role of hormones and genetic
controls in cancer. All agree that there is a connection, but no one
knows exactly what it is. However, in his article Dr Hahn discusses
a study done by Dr David Felman (and published in the June Nature)
that I find intriguing because of how it may relate to the role the
animal's behavior and his/her relationship with the owner plays in
cancer. In a very tiny nutshell, the study looked at two gene mutations
that lead the stress hormones cortisol and cortisone to trigger the
growth of later stage cancer cells.
Because cortisol is also one of the hormones that's elevated when
stress results in animal behavioral problems which, in turn, may result
from human-animal relationship ones, it would seem that avoiding such
elevations of this hormone by treating bond and behavioral problems
could conceivably lower the probability of cancer in some animals,
or improve the survival chances of those already afflicted with the
disease. Although such a hypothesis might seem to require too great
a leap of credibility for those who associate cortisol and cortisone
with those drugs that counter inflammation and itching, another effect
of these hormones is that they undermine the immune response.
So while they may benefit animals who encounter occasional stresses
of brief duration, these same substances may seriously undermine the
health of those who daily live in stressful environments. In that
case, not only will these animals have a higher probability of developing
stress-related behavioral and medical problems (such as aggression
or separation anxiety displays, irritable bowel syndrome or chronic
or recurring urinary tract conditions), these animals' taxed immune
response may experience more difficulty recognizing and dispatching
mutant cells before they multiply and form cancers.
Currently the exploration of the nonreproductive effects of sex hormones
is in its infancy and, unlike the rise of feminism which challenged
the philosophy underlying hysterectomy and ovariohysterectomy in women,
many of those who normally claim to speak for the animals are usually
quiet about how sterilization may affect companion animals. Like Dr
Hahn, I, too, have reviewed the literature and am not sure what to
tell clients. However, I do know that unless we can free the subject
from the emotional cocoon that has protected spay and neuter from
objective scrutiny all these years, our pets won't be able to benefit
from the knowledge that is slowly, but surely, being generated on
this subject.
Myrna Milani, BS, DVM
TippingPoint Animal Behavioral Consulting Services
Charlestown, New Hampshire
www. mmilani.com
Permission was granted by Dr Milani to
include this article at the wwwGreatDaneLady.com
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