Rats are genetically susceptible to tumors. In fact, tumors are one of the most common health conditions in rats 18 months and older. This article aims to help you to be able to identify tumors on your rat and provide information on the treatment options as well as tips on how to care for a rat with a tumor.
If you think that your rat might have a tumor, you need to seek veterinary attention as soon as possible. Not all lumps you find on rats are tumors or cancer. In most cases, the earlier treatment is initiated, the better the outcome for a rat with a tumor. The most common treatment is surgical excision of the lump. Feeding a diet high in antioxidants and low in calories and carbohydrates will prevent some tumors and slow the growth of certain types of cancer.
How Do I know If My Rat has A Tumor?
Familiarizing yourself with what is typical for your rat will help you to be able to spot anything inauspicious early on. Giving your rat a thorough physical check every few weeks is one of the best ways rat owners can help their vets pick up on diseases as soon as abnormalities become apparent.
Rats are a little too good at hiding symptoms, and knowing what to look out for will help identify problems before they become life-threatening. You can have a look at this step-by-step guide on how to do a physical exam on your rat at home.
Not all tumors are externally visible, and the symptoms you might notice initially are highly dependent on the location of the tumor. Pituitary tumors, for example, are a common tumor in rats that grows on the pituitary gland near the base of the brain. In these cases, you may notice symptoms such as confusion or a head tilt and eventually even blindness.
As another example, tumors in the mouth may first present with the rat having difficulty eating and eventually losing weight.
In the advanced stages, incredibly aggressive or cancerous tumors that have spread to other organs, you may notice lethargy, weakness, weight loss, a scruffy coat, and reduced appetite. It’s extremely easy to miss tumors in less prominent locations, but as a general rule, the sooner we identify and treat, the better the prognosis.
When examining your rat, pay special attention to any new lumps or bumps. Not all lumps are tumors. Cysts, which are fluid-filled sacs, usually under the skin, abscesses, and enlarged lymph nodes, can all look like tumors. Therefore, taking your rat to a vet is crucial if you notice abnormal bumps. Your vet will likely need to do further diagnostic tests such as a fine needle aspirate or radiographs. In some cases, an MRI or PET scan will be beneficial to provide a prognosis and appropriate treatment plan for your rat.
If you have an unsterilized female rat, check her entire underside regularly. Unsterilized female rats are especially susceptible to mammary gland tumors (breast cancer) as the growth of this type of tumor is encouraged by certain female hormones. Rats also have pervasive mammary tissue so check the entire belly all the way from the shoulder or axilla down to the inguinal or tail region. Although mammary tumors are much more common in females, male rats may also develop mammary tumors, so don’t neglect to check your rat-boys as well.
If you would like to read more on the warning signs of an ill rat, this article explains which symptoms to look out for and when to know whether you need to take your rat to the vet. As a general rule, rats should be taken to the vet for a general checkup every six months from the age of 18 months.
Types Of Tumors in Rats
Tumors are classified into two main categories, namely benign or non-cancerous and malignant or cancerous.
Malignant or cancerous tumors are usually fast-growing, invade the surrounding tissue, and tend to spread throughout the body. The spread of cancerous tumors, called metastases, is not always apparent at first. Metastasis of malignant tumors may spread to internal organs such as the lungs or liver, and symptoms of spread to these organs may not be apparent until the metastasized tumors are extensive and start to interfere with the normal functioning of the organ it has spread to. An MRI or PET scan is beneficial to pick up on the early spread of tumors.
Suppose a cancerous tumor has spread from its primary growth to affecting another organ or has appeared on a different part of the body, the chance of there being more tiny tumors growing in other areas of the body is extremely high as the tumor cells have already made their way into the vascular and lymphatic system. Unfortunately, these cases often carry a poorer prognosis.
Benign or non-cancerous tumors are usually slow-growing and do not spread to other organs or body parts. In these cases, surgical excision is typically curative, provided that the tumor is small enough for the surgeon to get wide enough margins to ensure that all tumor cells are removed and still be able to close the wound.
- Pituatary tumors: usually malignant growths asssociated with the pituatary gland near the base of the brain
- Mammary tumors: more common in in tact females but male rats can occur in male rats as well
- Pheochromocytomas: benign tumors of the adrenal glands
- Fibromas: benign growths of connective tissue, most common in the skin or just under the skin
- Tumors of the uterus and ovaries in female rats
- Lipomas: beningn growths of fatty tissue
- Testicular tumors in male rats
This list is just a sprinkle of some of the most common tumors of rats and is not nearly exhaustive. All cells have the potential to become cancerous, so the list of possible cancers is much longer than your rat’s cute tail.
Treatment Options For Rats With Tumors
Surgical Removal Of The Mass
In most cases, surgical excision of the tumor as soon as possible will be recommended. Exceptions to this will be tumors in inoperable locations (for example, pituitary tumors), tumors that are too large to remove (for example, clean surgical margins or skin closure after excision will not be possible), or if your rat carries a high anesthetic risk (for instance, a geriatric rat or a rat with concurrent conditions such as heart disease).
If your rat has a mammary tumor, it will be best to have them sterilized simultaneously as having surgical excision of the tumor performed to prevent re-growth of the tumor.
In cases where surgical excision is not an option, such as when the tumor is in an inoperable location, is too large to remove, or the rat will not tolerate anesthesia, you and your vet may decide to keep your rat as comfortable as possible.
As your rat’s health starts to decline, you may have to start applying extra measures to keep them comfortable. Provide them with soft bedding and a cage where they will have easy access to food and water. Use low, flat water bowls and feed easy-to-eat food such as soaked pellets or banana slices. If they cannot feed themselves, you may have to hand feed your rat with a syringe.
You will have to clean your rat daily as frail rats are often incapable of cleaning themselves. Check for urine scalding on their bellies. You may also have to clean their ears and face as they will be unable to clean it themselves.
Speak to your vet about appropriate pain medication if you think that your rat may be experiencing pain (have a look at this article on how to identify signs of pain and what medication is safe to give).
For more detail on how to look after a frail rat, please look at this article outlining multiple aspects of caring for ill or elderly rats.
If you have a few rats sharing an enclosure and one is suffering from a medical condition, you do not have to separate it from the other rats unless the other rats are bullying the ill rat. Rats will often care for ill cagemates and will provide company and ‘moral support’, so to speak. If it interests you, you can read more about the research on how rats show empathy in this article.
In some cases, euthanasia is the best thing you can do for your pet rat. I included this as a treatment option as sometimes it is better to spare them suffering than to do nothing at all. I am sure I can speak on behalf of nearly all vets here in saying that vets are there to help you provide the best possible care for your rat and will be more than happy to help you evaluate your rat’s quality of life. Your vet should be a trusted ally when it comes to making these crucial and extremely tough decisions when it comes to your pet rat’s health.
Evaluating the quality of life is one of the ways we determine whether euthanasia is a kind option. We can judge whether a rat has a good quality of life by looking at the amount of time they spend doing things that rats enjoy doing. So if your rat still boggles when you offer them their favorite treat or still enjoys spending time outside of the cage or following you around, they may be doing just fine.
But if you find that your rat spends the whole day sleeping, constantly has urine scalding or shows signs of pain, and does not eat unless you place the food right in front of their nose, I would encourage you to talk to your vet.
I am a huge advocate for preventing or ending suffering. If you think that your rat may be near their end (and owners often have a good sense of when this is – trust yourself!), having them humanely euthanized by your vet may be the kindest thing you can do for your rat in such a situation—Euthanasia, when done correctly and by a veterinarian, is painless.
At the very least, let your vet have a look and help you make the decision. Sometimes our judgment becomes clouded with emotion when our own pets are having a difficult time. Having a trusted vet by your side in situations like these will help you to make a decision in the best interest of your beloved rat.
What About Chemotherapy and Radiation?
Chemotherapy and radiation are not a standard treatment option for rats with malignant cancers for a few reasons:
In the case of radiation therapy, your rat will have to be fully anesthetized every time they have to get treatment in order to lie still for the treatment. Second, rats are such tiny creatures that even the most concentrated, smallest of radiation will still radiate your rat’s entire body, which will lead to healthy organs and tissues becoming radiated. In most cases, the risk of repeated anesthesia and radiation damage to healthy tissue is too significant to justify the benefit of treating the cancer cells.
Most chemo drugs need to be given into a vein weekly for a few weeks, depending on the chemotherapy drug used. However, it is very tricky to get vein access on a creature as small as a rat, and they often need to be anesthetized for this delicate procedure.
Both chemo and radiation will entail recurrent potentially stressful treatments for your rat, along with the known side effects of chemo and radiation. A biopsy and possible MRI will be necessary before considering this as treatment options as the type of cancer, and the location will determine the protocol used. Although this is not common practice, you can discuss the risks versus the benefit with your vet if this is something you consider.
How to Prevent Tumors In Rats
A reduced-calorie diet is strongly associated with an increased life span and reduced disease incidence, as found in numerous studies on calorie restriction and longevity (1, 7, 9). Rats fed a reduced-calorie diet had a lower incidence of tumors than rats fed free access, high-calorie diet.
If you would like to read more on preventing over-feeding in rats, look at this article.
Providing ample opportunity for your rat to explore, run around and be active will not only help keep their weight down (which, as mentioned above, will help prevent tumors in itself) but may reduce the incidence of tumors as well (5).
You can encourage activity by allowing supervised time spent outside the cage in a rat-proof environment. The recommended amount of time your rat should be allowed to spend outside their cage is at least 30 minutes per day. You can read more on that in this article.
Adjust Their Diet
In addition to preventing over-eating, providing your rat with a diet high in antioxidants and omega-three fatty acids (DHA and EPA) will help protect the DNA of aging cells from becoming damaged. Abnormal or damaged DNA is one of the main causes of tumors. In this article, I wrote about the ideal diet for an aging rat, including food high in antioxidants. So if you want to know more, go check it out!
Vitamins like A, E, and C and grape seed oil are note-worthy antioxidants. Vitamin A, E, and C are abundant in berries or fresh vegetables. So, make sure to feed a portion of fresh food every day. A few rounds of carrots, baby corn, peas, strawberries, and blueberries are great options.
In addition to that, and interestingly, feeding apples have also been shown to prevent mammary tumors in female rats (6). So feel free to add more of this tasty snack to the diet of your male and female rats alike.
Feeding a low carbohydrate, high fat, high protein diet has also shown to be beneficial in reducing the growth of tumors in rats (3, 4). Insulin and blood glucose play an important part in the growth of cancer cells. Feeding a lower carbohydrate diet will help reduce insulin and blood glucose spikes which can potentially reduce the growth of tumor cells.
Avoid sugary treats such as sweets and high carbohydrate foods such as pasta and bread. Feed veggies and protein-rich foods such as scrambled eggs instead.
The research on the benefits of a low-carbohydrate diet for treating and preventing cancer and other age-related conditions is fascinating. I will be writing more on this topic soon, so keep an eye out for that!
Not all lumps are tumors, not all tumors are cancer, and not all cancer has to be fatal. Finding a lump on your rat can be frightening, but being proactive by examining your rat regularly and taking them to the vet for checkups every six months from the age of 18 months will help to pick up on abnormal lumps and get them the necessary treatment as soon as possible.
- Gross, L. and Dreyfuss, Y., 1990. Prevention of spontaneous and radiation-induced tumors in rats by reduction of food intake. Proceedings of the National Academy of Sciences, 87(17), pp.6795-6797. https://www.pnas.org/content/87/17/6795.short
- Holloszy, J., Exercise Increases Average Longevity of Female Rats Despite Increased Food Intake and No Growth Retardation, Journal of Gerontology, Volume 48, Issue 3, May 1993, Pages B97–B100, https://doi.org/10.1093/geronj/48.3.B97
- Ho, V., Leung, K., Hsu, A., Luk, B., Lai, J., Shen, S., Minchinton, A., Waterhouse, D., Bally, M., Lin, W., Nelson, B., Sly, L. and Krystal, G., 2011. A Low Carbohydrate, High Protein Diet Slows Tumor Growth and Prevents Cancer Initiation. Cancer Research, 71(13), pp.4484-4493. https://cancerres.aacrjournals.org/content/71/13/4484.short
- Jackson, C., Weis, C., Chen, J., Bechtel, D. and Poirier, L., 1998. Relative contribution of calories from dietary fat, carbohydrate, and fiber in the promotion of DMBA‐induced mammary tumors in Sprague‐Dawley rats. Nutrition and Cancer, 30(3), pp.194-200. https://cancerres.aacrjournals.org/content/50/18/5710.short
- Kritchevsky, D., 1990. Influence of Caloric Restriction and Exercise on Tumorigenesis in Rats. Experimental Biology and Medicine, 193(1), pp.35-38. https://journals.sagepub.com/doi/abs/10.3181/00379727-193-42986
- Liu, R., Liu, J. and Chen, B., 2005. Apples Prevent Mammary Tumors in Rats. Journal of Agricultural and Food Chemistry, 53(6), pp.2341-2343. https://pubs.acs.org/doi/abs/10.1021/jf058010c
- Mukherjee, P., Sotnikov, A., Mangian, H., Zhou, J., Visek, W. and Clinton, S., 2021. Energy Intake and Prostate Tumor Growth, Angiogenesis, and Vascular Endothelial Growth Factor Expression. https://academic.oup.com/jnci/article/91/6/512/2549359?login=true
- Russo, J. and Russo, I., 1996. Experimentally induced mammary tumors in rats. Breast Cancer Research and Treatment, 39(1), pp.7-20. https://link.springer.com/article/10.1007/BF01806074
- SEILKOP, S., 1995. The Effect of Body Weight on Tumor Incidence and Carcinogenicity Testing in B6C3F1 Mice and F344 Rats. Toxicological Sciences, 24(2), pp.247-259. https://www.sciencedirect.com/science/article/abs/pii/S0272059085710287
- Taylor, I. and Mowat, V., 2020. Comparison of longevity and common tumor profiles between Sprague-Dawley and Han Wistar rats. Journal of Toxicologic Pathology, 33(3), pp.189-196. https://www.jstage.jst.go.jp/article/tox/33/3/33_2020-0005/_article
- Weber, K., 2017. Differences in Types and Incidence of Neoplasms in Wistar Han and Sprague-Dawley Rats. Toxicologic Pathology, 45(1), pp.64-75. https://journals.sagepub.com/doi/10.1177/0192623316672075?url_ver=Z39.88-2003&rfr_id=ori:rid:crossref.org&rfr_dat=cr_pub%20%200pubmed