Rat/Mice Diseases - Tumours

Benign mammary tumor in rat
  • Along with respiratory infections, tumors are one of the most common health problems and causes of death in rats and mice, 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, and therefore easily removed by surgery.
  • Although they can grow as fast as malignant tumors, they don't cause as much damage and they don't metastasize (spread to other parts of the body).
  • Although benign tumors won't usually cause death directly, a tumor can grow so large that the rat and mice has difficulty moving around and can't eat enough to support both the tumor and normal body functions. Most pets are euthanized before reaching this stage, if the tumor isn't removed.
  • In contrast, malignant tumors, also called cancer, usually invade and damage nearby tissues and also metastasize.
  • Death will be caused by the failure of damaged organs. Because cancerous tumors intertwine with normal tissues, surgery is usually impossible in rats and mice.
  • In most cases, cancer involves the internal organs, so symptoms often aren't seen until the disease is well advanced and euthanasia is the only alternative.
  • The most common tumors in aged rats are pituitary adenomas and mammary fibroadenomas.

  • Symptoms:
    The symptoms of cancer may include a skin ulcer, ulcerated tumor, or bleeding from a lump, a distended abdomen, weight loss, and lethargy.
    • Types
      • Keratocanthomas
        1. Benign tumor of the skin that develop in the chest, back or tail.
      • Mammary Fibroadenomas
        1. The most common kind of reproductive tumors in rats and mice.
        2. Can be found in the mammary (breast) tissue, and are usually benign (not malignant).
        3. Benign mammary tumors are usually distinct lumps just under the skin that are only loosely attached.
        4. Found in both female and male.
        5. These tumors are often stimulated by estrogen and usually occur after rat and mice stops ovulating at around 18 months of age.
        6. About half of all females will get mammary tumors, and it’s common for them to get several during their life either at the same time or one after the other.
      • Tumors in rats
      • Mammary Adenocarcinomas
        1. Malignant (aggressive and spreading) tumors that are found under the skin anywhere on the underside of the body, from the chin to the tail, as rats have widely distributed mammary (breast) tissue.
        2. Typically these tumors are soft, round, or somewhat flat growths that can be moved.
        3. Malignant mammary tumors most commonly appear in the vulva/anus area, but not all tumors in this area are malignant.
        4. A mammary tumor that appears dark is almost sure to be malignant.
        5. Malignant mammary tumors also commonly develop ulcers and abscesses.
      • Pituitary Gland Tumors
        1. It is an adenoma (benign tumor) of the pituitary gland, which lies beneath the brain.
        2. It is Common in female rats and mice.
        3. As the tumor grows it presses on the brain and eventually causes neurological impairment.
        4. Due to the position of the tumor symptoms include head tilting, depression, paralysis and seizures.
        5. These tumors usually lead to sudden death.
      • Testicular Tumors
        1. Found in the testes of male rats and mice.
      • Zymbal’s tumors
        1. Found at the base of the ear in older rats; they are relatively infrequent

  • mammary tumors in rats
  • Treatment:
    • Your veterinarian will likely recommend surgical removal of the tumor, since some types of tumors can grow and spread to other locations in the body. It is best to remove the tumors as soon as possible in order to avoid the worst complications. Chances of recurrence may also be minimized if the tumor is removed early.
    • In case of testicular tumors, and in some cases of mammary adenocarcinomas, the entire testis or mammary gland will be removed along with the tumor to avoid metastasis (spread) of the tumor.
    • Surgery is not recommended for malignant mammary tumors, as they quickly grow back, but they can be successfully treated with tamoxifen.
    • Recommended treatment for Pituitary Gland Tumors is with antibiotics and prednisone.Treatment with prednisone for some cancers other than mammary cancer can slow their growth.
    • There is some evidence that a high fat/high protein diet is best for cancer patients.

  • Prevention:
    • There are four ways to try to prevent tumors in your rat/mice.
    • First, by feeding your pet a low fat, low calorie diet which is also low in amines and nitrates (when these natural components of some plants combine in the stomach they are carcinogenic).
    • Many studies link obesity and a high fat diet with tumors.
    • Second, you can try to locate a breeder who has been selectively eliminating the tendency for tumors from their stock.
    • This type of breeding can be difficult, because tumors usually occur in rats over a year old, after they can already have great-great grandchildren.
    • The third way, and probably the most reliable at this time, is to choose male rats and mice over female rats and mice.
    • While males can also get tumors, the benign mammary tumors that are so common in females are relatively rare in males.
    • And lastly spaying or neutering your pet may help reduce the likelihood of your rat and mice getting breast tumors (usually fibroadenomas) but there are no guarantees.