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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 by surgery depending on their location.

In contrast, malignant tumors, also called cancer, usually invade and damage nearby tissues. They sometimes also metastasize, or spread, but not always. Death can be caused by failure of damaged organs. The symptoms of cancer can include a skin ulcer, an ulcerated or bleeding tumor, an infected lump, an abscess that won't heal, 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. It can be worth trying to remove a malignant tumor as this can give the rat many more months of quality life, depending on the type of cancer. I know of 2 cases of fibrosarcoma where removing most of the tumor gave the rat up to 8 more months!

Mammary Tumors

The most common tumor in rats is the benign mammary tumor, most being a fibroadenoma (fibro--from connective tissue, aden--from a gland, oma--a benign tumor). These tumors are often stimulated by estrogen and usually occur after a rat stops ovulating at around 18 months of age. About half of all female rats will get a mammary tumor, and it's common for them to get several during their life. The most common locations for mammary tumors are in the armpits and in the belly or groin area, although because female rats have widespread mammary tissue, they can occur anywhere on the body. It's a good idea to feel your rat all over frequently so you can identify tumors early.

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. It is also common for mammary tumors to contain milk. 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 some benign tumors also feel attached.

A much less common cause of a lump in the breast area is a blocked milk duct. I know of one case. The firm 1/2" X 1/4" lump was attached to the nipple but not anywhere else. This rat had weaned her babies only a week or two before the occurrance, but blocked milk ducts can also occur in non-nursing females. The treatment of warm compresses every 4 hours cleared it up in a week.

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 3rd most common cause of death in female rats. Sixteen percent of my rats have had pituitary tumors.

As the tumor grows it presses on the brain and eventually causes neurological impairment. Symptoms may appear slowly or quickly. Commonly, the first symptom is a loss of coordination, followed by some paralysis. One symptom that is diagnostic of a pituitary tumor is a quite distinctive posture: first the front, then the hind legs are held out stiffly forward and can not be flexed by the rat. However, other possible symptoms, including seizures, a head tilt, circling, and lethargy, can also have other causes. Perhaps some day, a blood test will be able to identify a pituitary tumor. Until then, all you can do cover all the bases.

The recommended treatment for neurological impairment is with both steroids and antibiotics. These can help reduce the size of a tumor and temporarily relieve the symptoms, and is also the recommended treatment for an inner ear infection or stroke. If despite treatment the rat is no longer able to feed herself, it will be time to have her euthanized.

Other Types of Tumors

Another fairly common tumor in rats is a fibroma. Because they derive from fibrous tissue they are usually quite hard, but they are benign and are easily removed.

The most common type of cancer in rats is probably squamous cell carcinoma. I’ve seen 4 of them, 2 on the face, one from the eyelid, and one under the jaw. This type of tumor is most common on the face and head and should be suspected in any case of swelling or abscess in this area on rat.

I’ve known of two cases of histiocytic sarcoma. This is a cancer of the immune system, and in the case I saw there was no tumor in evidence, only abscesses resulting from the depressed immune system. I've known of 2 cases of lymphosarcoma in the chest, and I currently know of one case of leukemia.

I’ve known of 3 cases of benign tumors growing in the vagina and it appeared that for the tumors to be successfully removed, the vagina itself would need to be removed.

Non-Surgical Treatment

In lab studies, tamoxifen has helped to treat and prevent both benign and cancerous mammary tumors and pituitary tumors (which are inoperable) in rats. However, I know of several people who have tried tamoxifen to treat benign mammary tumors with little success. However, I know of several cases where it has worked really well for cancerous mammary tumors. I highly recommend tamoxifen rather than surgery for tumors appearing near the vulva which are filled with a dark fluid. These tumors are usually malignant and I have found that surgery is not successful in removing them.

Tamoxifen works by blocking estrogen receptors in tissue, so it is only effective for tumors which are stimulated by estrogen, but it might be worth a try for all mammary tumors as it is cheaper and less stressful than surgery. You should start it as soon as you notice the tumor. Your vet can call in a prescription to a human pharmacy. The dose is 1-3 mg/lb once a day. You will need to give it for several weeks, and you may not see any shrinkage of the tumor for 2-3 weeks, so don't give up too soon. Be sure to measure and record the size of the tumor at the start of treatment so you can keep track. Using it along with melatonin (try 0.2 mg/day) seems to boost its effect.

Keep in mind that tamoxifen has a side effect of reducing the number of platelets in the blood. This interferes with the blood’s ability to clot. If you decide to have a tumor removed, you should stop tamoxifen treatment for 2 weeks before surgery. Tamoxifen should not be used in male rats or spayed females. For more on tamoxifen click here.

An alternative to tamoxifen is leuprolide, which blocks the release of estrogen. In one study it was slightly more effective against induced tumors, but it is rather expensive. The suggested dose is 20-50 mcg/lb and one injection of leuprolide depo lasts a month.

Another treatment that has been shown to treat and prevent mammary tumors induced in the lab is conjugated linoleic acid (CLA). This compound has even been shown to help rats lose weight! When given at 75 mg a day, the body fat of rats was reduced by 23%.

There are some other alternative treatments you can try for tumors. Shark cartilage helps to prevent the formation of new blood vessels, which tumors need to grow. This can be quite effective if you start it as soon as you notice the tumor. I know 3 cases where it has worked. The best quality 100% pure cartilage is expensive, but it goes a long way. Try 36 mg per day. It may work better when combined with co-enzyme Q-10 (try 3 mg/day) and you can also use it along with tamoxifen.

Some other supplements that may help include alzium, IP-6 (inositol hexaphate), cat's claw, lactoferrin, liquid chlorophyll, AHCC (activated hexose correlate compound), essiac tea, ellagic (red raspberry seed extract), and aloe vera (be sure it is made to be taken orally). Look for these in your health food store and try 1/10th the human dose. Another very promising treatment is MGN-3 which can be ordered from LaneLabs at 800-510-2010. Again, for all of these try 1/10th the human dose.

Tumor Surgery

If non-surgical treatment is not effective for a tumor, surgery is the only remaining treatment. In twelve years I did more than 300 surgeries to remove tumors from rats, and only a few were malignant. I have removed tumors from only a few males; the vast majority were females, almost all of them with benign mammary tumors. I had nearly 100% success removing this type of tumor.

The smaller the tumor, the more easily it can be removed. But it's never too late to have a tumor removed as long as your rat is otherwise in good health. I successfully removed a tumor that weighed 340g from a rat that only weighed 244g!

I 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 fibroma 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. As long as a rat is otherwise in good health, this minor surgery can be performed on a rat of any age. While there is a good chance that any rat could develop another tumor later, the surgery may save her life and improve the quality of her life for months to come.

The cost to remove rat tumors can vary greatly. In Chico (a town of 70,000) the charge is $100-150 depending on the size of the tumor. The fee is usually higher in larger cities. It's cheaper and easier on your rat in the long run to have her spayed when she is young. You can also have a rat spayed at the same time that a tumor is removed. (See Preventing Tumors below.)

If your rat is suspected to have a malignant tumor, it can still be worth it to have the tumor removed. I know of two cases of fibrosarcoma where having the tumor removed gave the rat 8 months or more of comfortable life. However, I've found it's rarely worth it to remove a malignant mammary tumor or squamous cell carcinoma.

If you decide not to have a tumor removed, you can expect it to keep growing. Mammary tumors especially can grow as big or bigger than the rat herself. Within a few months, or even weeks, 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, carbohydrates, and vitamins, because the tumor will be drawing resources and energy from her body.

Preventing Tumors

There are four 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 similarly decreases the incidence of pituitary tumors. Spayed rats also tend to live longer than unspayed rats. In one study, spayed lab rats lived almost one year longer than unspayed rats. Spaying is most effective at 3-6 months, but has benefits at any age. Spaying will often cause mammary tumors to shrink.

The cost of having a rat spayed is usually much less than having a tumor removed (about the same as a cat spay), 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. Or, you can give your female rats tamoxifen, starting at age 18 months, or with their first tumor. However, in several cases I know of rats who eventually developed a strong dislike of tamoxifen and refused to take it.

The third way to prevent tumors is to choose male rats over female rats. While males can also get tumors, the benign mammary tumors and pituitary tumors that are so common in females occur in only about 4% of males.

Finally, diet can help prevent cancer. You should feed your rat a nutritious low fat, low calorie diet that includes fresh fruits and vegetables that have been shown to have cancer preventing components, such as cooked dry beans (especially soybeans), brocolli, and tomatoes. One study found that DHEA given at a dose of 25 mcg/day, helped to protect against induced mammary tumors. Other studies showed that feeding the rats miso, a soybean product, as 10% of their diet, also had a protective effect against induced tumors. When combined with tamoxifen, the miso diet was almost 100% effective in preventing the tumors. Another study found that flax seed comprising from 2.5-10% of the diet also had a protective effect against mammary tumors. Some of the non-surgical treatments discussed earlier, especially CLA, have preventative effects as well.

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