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by Debbie “The Rat Lady” Ducommun
Along with respiratory
infections, tumors are one of the most common health
problems and causes of death in rats, especially in females. There are two main types of tumors, benign and malignant. Benign tumors
are almost always encapsulated in a membrane and separate from nearby
tissues. Although they can grow as
fast as malignant tumors, they don’t usually
cause as much damage and they don’t metastasize (spread to other parts of
the body). Benign tumors can cause death by pressing on vital organs,
bleeding internally, or by growing so large that the rat has difficulty moving
around and can’t eat enough to support both the tumor
and normal body functions. Benign tumors can often be removed depending on their location.
In contrast, malignant tumors, also called cancer, usually invade and damage
nearby tissues. They sometimes also
metastasize (rarely in rats). Death
can be caused by failure of damaged organs or mechanical interference with
normal functions, such as eating.
The symptoms of cancer can include a skin ulcer, infected lump, or
abscess that won’t heal, an ulcerated or
bleeding tumor, a distended abdomen, weight loss, and
lethargy.
In some cases, cancer
involves the internal organs, so symptoms often aren’t seen until the
disease is well advanced and euthanasia is the only alternative. This is why it’s important to give
your rats a weekly exam. Many
benign tumors can be removed, depending on the location,
and surgery for some types of cancer can give a rat many more months of quality
life. Some tumors
can be temporarily shrunk with prednisone.
Mammary Tumors
The most common tumor in female rats is the benign mammary tumor, most being a fibroadenoma
(fibro—from connective tissue,
Mammary tumors often start out squishy and flat, and then become
more firm, but they can also be quite hard from the start. Because the tumors
grow so quickly, a portion will sometimes outgrow its blood supply, die and
become necrotic and filled with pus. Mammary tumors
also commonly contain pockets of milk, which can grow very quickly.
Benign mammary tumors are usually distinct lumps just under the skin that
are only loosely attached. When you
feel the lump, you can usually move it separately from the skin and underlying
muscle. If your rat gets one of these tumors, you can
be 99.9% sure it’s benign. If
a tumor feels tightly attached to the underlying
tissue, this can be a sign that it is malignant, but I have found that some benign
tumors also feel attached because they are underneath
connective tissue and turn out to be easily removed by surgery. Benign mammary tumors
can grow huge (up to 4" across). They tend to have a basically round shape
that tends to protrude. A malignant mammary tumor
will rarely get more than 2" across and tends to stay more flat.
In my experience,
malignant mammary tumors most commonly appear in the
vulva/anus area, but not all tumors in this area are
malignant. The location alone is not enough for diagnosis. Malignant mammary tumors
can also appear under the arm. A mammary tumor that appears
dark is almost sure to be malignant.
Malignant mammary tumors also commonly develop
ulcers and abscesses. A benign mammary tumor
won’t develop an ulcer until it is huge. A needle biopsy is not usually
helpful in the diagnosis of the type of tumor.
Surgery is not recommended for malignant mammary tumors, as they quickly grow back, but they can be successfully treated with tamoxifen. See Tamoxifen to Prevent and Treat Tumors.
Tamoxifen does not seem to be an
effective treatment for benign mammary tumors. They must be surgically removed. If you decide not to have a benign
mammary tumor removed, you can expect it to keep
growing, until it is as big as the rat herself. Within a few months you must be prepared
to have your rat euthanized when she is no longer
enjoying life. In the meantime, you
can help your rat maintain her quality of life by making sure she eats a very
nutritious diet, high in protein, fat, and vitamins, because the tumor will be drawing resources and energy from her body.
A more rare cause of a
lump near a nipple is a blocked milk duct or inflamed mammary gland. Treatment with warm compresses 2-3 times
a day and an antibiotic should resolve this within a week.
Male rats can also get
mammary tumors, but they are uncommon and almost
always benign.
Pituitary Tumors
The second most common
type of tumor in female rats is an adenoma (benign tumor) of the pituitary gland, which lies beneath the
brain. In fact, this is probably
the third most common cause of death in female rats. The incidence in my unspayed
female rats has been 20% and in my male rats 7%.
As the tumor
grows it presses on the brain and eventually causes neurological
impairment. Symptoms may appear
slowly, over a period of a few days or a few weeks, or quickly. These tumors
are highly vascular and in some cases they can hemorrhage,
which can cause acute severe symptoms, such as paralysis, seizures and
death. It also seems that a slight hemorrhage from the tumor can
cause symptoms that later clear up.
For a typical pituitary tumor causing a slow onset of symptoms, the usual first
symptom is a loss of coordination, followed by some loss of function of the
arms and legs and mouth. Sometimes
the rat is hyperactive, and she may walk in circles and run into objects. Some rats with pituitary tumors become very infant-like and cuddly and must be hand-fed.
One symptom that is common
with a pituitary tumor is a quite distinctive
posture: first the front, then the hind legs are held out stiffly forward and
cannot be flexed by the rat. When
you pick the rat up, the arms and legs will often be held forward, although
sometimes the hands are curled.
Another behavior that is common is when a rat
butts her head up against your hand when you pet her.
Neurological symptoms,
including seizures, a head tilt, circling, and lethargy, can also have other
causes, such as a stroke, toxins, encephalitis, or an inner ear infection (head
tilt). Fortunately, the recommended
treatment for neurological impairment from any cause is with prednisone at 1
mg/lb twice a day and an antibiotic.
These can reduce the size of a pituitary tumor
and temporarily relieve the symptoms, but the treatment doesn’t always
help. In one case, prednisone did
not help but dexamethasone did help.
If the treatment is going
to help, you should see improvement in the symptoms within a week. The treatment then needs to be continued
for the rest of the rat’s life. I know of a few cases where this
treatment was able to give a good quality life to the rat for 3 to 10
months. If despite treatment the
rat is no longer able to eat, she should be euthanized.
Lumps on the Throat
A lump on the throat can
be an abscess, an inflamed salivary gland, a swollen lymph node, or a tumor. Salivary
glands can enlarge as an inflammatory response to either a viral infection
(SDA) or a bacterial infection. A
lymph node can enlarge in response to a bacterial infection or cancer.
A gland or lymph node can
swell up overnight, and an abscess can also appear quickly. Tumors tend to
grow more slowly. For a sudden
lump, try an anti-inflammatory first as this will usually cause a swollen gland
or lymph node to shrink within 12-24 hours. You can also wait to see if it is an
abscess. See Abscesses.
Other Types of Tumors
Another fairly common tumor in rats is a fibroma. Because these tumors
derive from fibrous tissue they are usually quite hard, but they are benign and
easily removed. They seem to be
most common on the side or back, but can be anywhere.
One of the most common
types of cancer in rats is squamous cell
carcinoma. I’ve seen 6 of them,
2 on the face, one from the eyelid, and 3 under the jaw, and I’ve heard
of several more. This type of tumor is most common on the face and should be suspected
with any swelling or abscess in this area.
Another very common place
for cancers to appear is directly below the ear. These cancers usually first appear as an
abscess, and you should suspect any infection in or around the ear of being
cancer. In one of my rats, such a tumor was diagnosed by pathology as a skin tumor, probably malignant, but the pathologist could not be
sure. In several of the tumors I’ve seen, the diagnostic symptom of this tumor is that the abscess eventually starts producing tiny
lumps of white tissue instead of pus.
The tumor can also start bleeding frequently.
Less Common Tumors
I’ve known of two
cases of histiocytic sarcoma. This is a cancer of the immune system,
and in my rat there was no tumor in evidence, only
abscesses resulting from the depressed immune system. I’ve known of 5 cases of lymphosarcoma in the chest, 2 in the abdomen, and one in
the skin. I know of 3 cases of leukemia. I know of 4 cases of fibrosarcoma,
all on the leg.
I know of one case of
malignant melanoma on the scrotum. I had a semi-hairless rat who
grew numerous sebaceous epitheliomas during his life,
and died at age 2 years of a basal cell carcinoma with sebaceous and epithelial
differentiation in his lung. I know of one case of bladder cancer.
I know of 5 cases of
benign tumors growing in the vagina and it appeared
that for the tumors to be successfully removed, that
portion of the vagina itself would need to be removed. This is possible in the rat, unlike dogs
or cats, as the vagina is completely separate from the urethra. I know of one case of a liposarcoma in the vagina, which was unfortunately also
attached to the bladder, so was inoperable.
The only treatment for
cancers other than mammary cancer is prednisone. It can slow the growth of some tumors.
Tumor Surgery
Since 1985 I have done
more than 1000 surgeries to remove tumors from rats,
and only a few turned out to be malignant.
I have removed tumors from only a few males;
the vast majority were females, almost all of them with benign mammary tumors. I have
good success removing this type of tumor.
Benign mammary tumors can be removed by minor surgery. The smaller the tumor,
the more easily it can be removed (although I do not recommend doing anything
for a lump the size of a pea as it could be just a cyst). But even huge tumors
can be removed as long as your rat is otherwise in good health and steps are
taken to prevent shock. I
successfully removed a mammary tumor that weighed
340g from a rat that only weighed 244g!
I’ve removed many tumors from rats well over two years old, so age should not
be the only factor when considering surgery. Because mammary tumors
and fibromas are just under the skin, the surgery to
remove them is minor, as opposed to major surgery which enters a body cavity,
and rats usually recover quite quickly.
In fact, even rats with congestive heart failure appear to tolerate
surgery well if their symptoms are controlled with medications.
If a rat younger than 24
months has a mammary tumor removed, consider having
her spayed at the same time to help prevent future mammary and pituitary tumors.
The cost for rat surgery
has gone up alarmingly in recent years.
In
Surgery may be beneficial
for some malignant tumors. I know of 3 cases of fibrosarcoma
where having the tumor debulked
gave the rat 8 months or more of comfortable life. However, attempting surgery on a squamous cell carcinoma just results
in a nasty wound that won’t heal.
Tamoxifen Treatment
Tamoxifen, which blocks estrogen receptor sites in tissue, is a highly effective
treatment for cancerous mammary tumors in rats. It is not a cure, but can retard the tumor for many months.
I know of 7 cases where it was highly effective and gave the rat up to a
year of quality life. However, tamoxifen does not seem to be an effective treatment for
benign mammary tumors.
A safety study showed that
tamoxifen is a safe treatment in adult female
rats. It only caused problems when
given to the rat for its whole life starting at 8-12 weeks of age. This study, Results of Three
Life-Span Experimental Carcinogenicity and Anticarcinogenicity
Studies on Tamoxifen in Rats, C. Maltoni et al, 1997, Ann. NY Acad
Sci, 837, 469-512), can be seen on the internet at www.annalsnyas.org/cgi/content/full/837/1/469?maxtoshow=&
HITS=10&hits=10&RES
Tamoxifen is readily available from
human pharmacies in the
You may not see any
shrinkage of the tumor for 2-3 weeks, so don’t
give up too soon; measure and record the size of the tumor
at the start of treatment so you can keep track. Laboratory studies show that using it
along with melatonin (try 0.2 mg/day) seems to boost its effect. Feeding soy products also seems to boost
its effect.
In a few cases, owners
have reported side effects from tamoxifen. The most common visible side effect
seems to be hair loss. In some rats
is has also seemed to cause fatigue.
A less obvious side effect
of tamoxifen is that it reduces the number of
platelets in the blood. This
interferes with the blood’s ability to clot. If a rat on tamoxifen
needs surgery, you should stop tamoxifen treatment
for 1-2 weeks before the surgery to prevent excessive and perhaps fatal
bleeding.
In one study leuprolide, which blocks the release of estrogen,
was slightly more effective than tamoxifen against
induced tumors, but it is very expensive. Having the rats spayed is less expensive
and more effective, so leuprolide does not seem
practical for most cases.
It might be worth trying
the new human drug Arimidex (anastrozole)
which prevents the production of estrogen.
Other Non-Surgical Treatments
A compound that has been
shown to both treat and prevent cancerous mammary tumors
induced (not natural tumors) in the lab is conjugated
linoleic acid (CLA). This compound has even been shown to
help rats lose weight! When given
75 mg a day, the body fat of rats was reduced by 23%. Another study found that DHEA given at a
dose of 6-12 mg/day protected against induced cancerous mammary tumors. Other
studies show that giving curcumin, an ingredient in
turmeric, reduced tumors induced in the lab. They gave about 150 mg per day.
Shark cartilage can help
to prevent the formation of new blood vessels, which tumors
need to grow. You must start it as
soon as you notice the tumor. I know 3 cases where it has helped but I
do not recommend using it for a tumor larger than a
marble, because it can cause the tumor to die. You can buy 200 g for $36 at
www.myvitanet.com. Try 360 mg/lb
per day mixed in food. It may work
better when combined with co-enzyme Q-10 (try 0.2 mg/day), and tamoxifen.
There is some evidence
that a high fat/high protein diet is best for cancer patients. It seems that a diet high in
carbohydrates may be more easily used by tumors. You might try giving soy baby formula plus
additional protein and B vitamins.
Preventing Tumors
There are 4 ways to try to
prevent tumors in your rats. The most effective way to prevent
mammary tumors in females is to have them
spayed. Three studies have shown
that spaying drastically reduces the incidence of these tumors,
from 40-70% to only 4%! Spaying
also decreases the incidence of pituitary tumors. In the laboratory, spayed rats also tend
to live longer than unspayed rats. For more on these studies, see the
website.
Spaying is most effective
at 3-6 months, but has benefits at any age. Lab studies showed that spaying will
often cause mammary tumors to shrink. The cost of having a rat spayed is
usually much less than having a tumor removed, and
since many female rats get multiple mammary tumors,
requiring multiple surgeries, having them spayed may actually save money in the
long run, as well as extending your rat’s life.
An alternative to spaying
is to give your female rats tamoxifen,
starting at age 18 months.
Laboratory studies have shown that it does reduce the incidence of both
benign and malignant mammary tumors and pituitary tumors when given preventatively. However, as I said earlier, many rats
object to taking oral tamoxifen over a long period of
time.
An alternative to giving tamoxifen orally is to use a pellet implanted under the
skin. This method has been used in
the lab, however, the pellets are expensive. A pellet lasting 90 days costs $22-32
each depending on how many are purchased (25-200 tablets which have a 3-year
shelf-life). You can buy them from Innovative
Research of America at 800-421-8171.
It may be more practical to have the rat spayed, which will accomplish
the same thing more effectively.
The third way to prevent tumors is to choose male rats over female rats. While males can get other tumors, the benign mammary tumors
and pituitary tumors that are so common in females
occur in only about 2-7% of males.
Finally, diet can help
prevent cancer. You should feed
your rat a nutritious low-fat diet that includes fresh fruits and vegetables
that have been shown to have cancer preventing components, such as cooked dry
beans (especially soybeans), broccoli, and tomatoes.
Several studies have shown
that feeding female rats miso,
a soybean product, as 10% of their diet, had a protective effect against
induced mammary tumors. When combined with tamoxifen,
the soy diet was almost 100% effective in preventing the tumors.
Another source of soy is a
whole soybean powder. This can be
added to water or soy milk to make a liquid for your rats to drink. Or, you can mix it with water to make a
thick paste, spread it on a greased pan to dry, and cut it into wafers.
Aother study found that
flaxseeds given at 375-1500 mg per day also had a protective effect against
mammary tumors.
Some of the non-surgical
treatments discussed earlier, especially CLA, have preventative effects as
well. A study showed that giving
pre-pubescent female rats about 150 mg of conjugated linoleic
acid (CLA) per day provided significant life-long protection against induced
breast cancer.
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