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This article is from the Rat Health Care booklet. Order one today! Check out the info at Rat Books
Tumors
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.
Here is a Pumkin with a large benign mammary
tumor. By her back leg, you can see
a staple from a previous tumor removal surgery.
This rat has a medium-sized benign mammary tumor in
her groin.
This rat has a medium-sized mammary tumor under her
left arm.
For pictures of surgically removed mammary tumors,
click here.
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, click here.
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. For more on these
studies, click here.
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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