Tumors in Rats

Causes, Treatment, and Prevention

White rat on black background
Rats are prone to developing tumors

CONEYL JAY/Getty Images

Tumors are relatively common in pet rats, and they can contribute to rats' relatively short lifespans. These growths, which can be malignant or benign, can occur in various places on a rat's body. Some cause pain or impede rats' daily activities. Because these animals are beloved by their owners for their friendliness and intelligence, early detection and treatment of tumors are critical. Treatment, primarily surgery, may help keep a rat more comfortable or extend its life.

What Is a Tumor?

A tumor is a mass or growth of abnormal tissue on a rat's outer body or internal organs. Tumors can range from less harmful benign cysts or lipomas (fatty tumors) to life-threatening cancerous tumors.

Tumors can develop on the skin of a rat where they are visible or internally where they may go unnoticed for some time. Some common types of tumors in rats include:

  • Mammary tumors
  • Lipomas
  • Cysts
  • Brain tumors

Symptoms of Tumors in Rats


  • Difficulty walking or climbing
  • Pain
  • Weight gain
  • Visible lump
  • Increased appetite
  • Bulging eyes
  • Misshapen head
  • Ataxia

Depending on the location, your rat's movement may be impaired which can lead to lethargy, poor appetite, and weight gain from a growing tumor.

Some tumors may cause an increased appetite in your pet rat. However, a rat that eats a lot of food but gains little to no weight may be experiencing a nutritional offset where the intake of nutrients is directed toward the growth of the tumor.

Brain tumors usually cause neurological symptoms as well as bulging eyes and a misshapen head due to tumor expansion. Rats with brain tumors may be ataxic and have problems getting around or appear wobbly.

Mammary Tumors

These are fast-growing and hormone-dependent tumors that respond to both estrogen and prolactin stimulation. They are most often seen in female rats that are not spayed, and malignancy is likely.


Also known as fatty tumors, lipomas are pockets of fat tissue that can surface on any part of a rat's body. They are rarely cancerous but may grow large enough to require removal.


Male rats are the most prone to developing cysts. Cysts are not considered tumors (unless it is a cystadenoma), but they look and feel like tumors. They are often found on a male rat's back near its sebaceous glands. Cysts can pop up from a simple skin infection or ingrown hair. They are usually quite firm and do not grow as large as a lipoma or mammary tumor.

Brain Tumors

Both benign and malignant brain tumors can be caused either by the presence of cancer or by an abnormality in the pituitary gland.

Causes of Tumors

Physiological/genetic and environmental factors (such as poor breeding or exposure to carcinogenic toxins) can contribute to the development of tumors, but no one knows exactly what initiates the abnormal growth of tissue in every case.

Diagnosing Tumors in Rats

Different types of tumors may be more obvious than others. Some tumors grow quickly and are easy to spot, while others are hidden internally and may go unnoticed until your rat starts having trouble getting around or seem painful when picked up.

After discovering a tumor, a veterinarian will perform a physical exam, x-rays, and/or ultrasounds to determine the shape and invasiveness of the tumor. A biopsy may also be required to find out if the tumor is cancerous.


Some growths may be small and manageable without surgery, but most tumors in rats get so large that they need to be removed due to the small size of the animal.

Mammary tumors and large lipomas are often surgically removed, especially if they are suspected to be cancerous or causing ambulation issues in your rat. Some growths are difficult to completely remove and regrowth is common.

Cysts are usually lanced, allowing fluid to ooze out. Cysts need to be watched for infection and can regrow, leading to later surgical removal.

Brain and certain types of cancerous tumors are inoperable in rats. Yet, some types of cancer can be treated with drugs like Tamoxifen (for estrogen-sensitive cancers), and supplements like turmeric and shark cartilage are reported to stunt a tumor's growth.

Rats with severe health issues, however, should be euthanized once their quality of life is compromised.

Prognosis for Rats with Tumors

The prognosis depends on the type and size of the tumor in a rat. Operable tumors may be removed, offering increased comfort and mobility, but many tend to regrow. Invasive cancerous tumors are often inoperable and may quickly impact a rat's quality of life.

How to Prevent Tumors in Rats

While there is no guaranteed prevention of tumors, feeding a rat a nutritious, low-fat diet may help prevent cancerous tumors in some rats. Several studies also show a decrease in mammary tumor formation in rats fed a diet high in miso, a soybean product. In addition, spaying or neutering your pet rat may help reduce the likelihood of it developing cancerous breast or reproductive organ tumors.

If you suspect your pet is sick, call your vet immediately. For health-related questions, always consult your veterinarian, as they have examined your pet, know the pet's health history, and can make the best recommendations for your pet.
Article Sources
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  1. Russo J. Significance of rat mammary tumors for human risk assessmentToxicol Pathol. 2015;43(2):145-170. doi:10.1177/0192623314532036

  2. Guideline for Tumor Burden Assessment in Rats and Mice. Michigan State University.

  3. Mammary Tumors in Rats. U.S. Department of Agriculture.

  4. Greaves, Peter et al. Proliferative and non-proliferative lesions of the rat and mouse soft tissue, skeletal muscle and mesotheliumJournal of toxicologic pathology vol. 26,3 Suppl (2013): 1S-26S. doi:10.1293/tox.26.1S

  5. Yasuno, Kyohei et al. Cutaneous hybrid cyst in a sprague-dawley ratJournal of toxicologic pathology vol. 25,2 (2012): 175-8. doi:10.1293/tox.25.175

  6. Mayer, Jörg et al. Extralabel use of cabergoline in the treatment of a pituitary adenoma in a rat. Journal of the American Veterinary Medical Association vol. 239,5 (2011): 656-60. doi:10.2460/javma.239.5.656

  7. Mathupala, Saroj P. et al. Microrna And Brain Tumors: A Cause And A Cure?. DNA And Cell Biology, vol 26, no. 5, 2007, pp. 301-310. Mary Ann Liebert Inc, doi:10.1089/dna.2006.0560

  8. Belanger, Janelle M. et al. Correlation Of Neuter Status And Expression Of Heritable DisordersCanine Genetics And Epidemiology, vol 4, no. 1, 2017. Springer Science And Business Media LLC, doi:10.1186/s40575-017-0044-6