Disorders of the mammary
glands can be worrisome in cats. Mammary
gland cancer is the third most common cancer in the cat.
Unlike dogs, in which only half of all mammary tumors are malignant,
mammary cancer in cats has a much worse prognosis, with 80 to 90% of mammary
tumors being malignant. While most
cases of mammary cancer occur in older cats (most commonly 10 to 12 years of
age), mammary cancer has been reported in cats as young as 9 months of age.
There is another condition of
the mammary glands called mammary hyperplasia, which is characterized by rapid
growth of mammary tissues. Although
the condition is considered to be benign, the condition can mimic mammary
cancer, which has a much worse prognosis. Mammary hyperplasia, however, tends to
occur in young, unspayed female cats instead of older cats. It is important to
differentiate mammary hyperplasia from mammary cancer, as the ages of affected
cats with these conditions can overlap. Mammary hyperplasia occurs as a result of the influence of
progresterone on the mammary glands. When
a young cat becomes pregnant (ovulation followed by fertilization) or
pseudo-pregnant (ovulation, but no fertilization), progesterone levels begin to
rise. Mammary tissues in cats have
many progesterone receptors, and the binding of progesterone to these receptors
can stimulate mammary gland development.
Although the condition is generally regarded as benign, in some cats,
this stimulation can lead to severe swelling, pain, ulceration, and infection of
the glands. Treatment involves
removing the source of the progesterone, although frequently, removal of the
progesterone doesn’t result in regression of the swelling.
In the case of unspayed females, removal of the progesterone source is
best accomplished by spaying. The
extent of the mammary gland swelling, however, can make a relatively simple
surgery like spaying much more difficult. The
swollen mammary glands tend to be very painful, and in my experience, the
incision site often becomes bruised and very tender afterward, causing a lot of
discomfort for the cat. My last
case of mammary hyperplasia was a disaster.
The client had unfortunately waited several days before bringing in the
cat for examination, and by the time I had a chance to examine the cat, several
of the glands had ulcerated and had become seriously infected.
When this happens, it is sometimes necessary to surgically remove the
swollen and infected gland(s). Unfortunately,
this cat, with a high fever and severe dehydration, was in no condition to be
anesthetized for any type of surgery. Emergency
care with intravenous fluids and antibiotics was unsuccessful, and the cat
developed septic shock followed by cardiac arrest.
She could not be resuscitated. She
was only 7 months old.
presence of progesterone receptors on feline mammary tissue offers the potential
for targeted endocrine therapy with drugs that block progesterone receptors.
Recently, the results of a study evaluating the use of aglépristone, a
progesterone blocker, in 22 young cats (aged 3.5 to 19 months) with mammary
hyperplasia were reported in the November/December 2002 issue of the Journal of
Veterinary Internal Medicine. Weekly
injections of aglépristone successfully treated nearly all cats in the study.
A marked and lasting response was seen in all cats after 1 or 2 doses.
Complete remission was observed in all but one cat.
Side effects were minimal and consisted of short-term skin irritation at
the site of injection. Two of the
cats were pregnant when they were treated, and as expected, those cats aborted
their kittens 2 to 5 days after the first injection. (Progesterone is necessary
to maintain pregnancy.) Those two
cats eventually developed endometritis, a uterine infection, and had to be
spayed as part of their treatment. They did fine afterward.
Questions as to why only a
minority of cats develop mammary hyperplasia after exposure to high levels of
progesterone, and why only young cats seem to develop the condition have yet to
be answered, and the pathogenesis of this condition requires further study.
is commercially unavailable in the United States. Hopefully, this will change
in the future.
mammary hyperplasia is an uncommon and relatively benign condition, many cats
develop significant clinical signs of illness, including lethargy, loss of
appetite, and painful, uncomfortable mammary glands.
Despite the benign description, most of the cases that I’ve encountered
have been fraught with complications. The
use of aglépristone as a simple weekly injection now makes treatment of this
condition much easier.