Common Cancers and Tumors in Rats


PetMD Editorial

Published Jun. 19, 2010

Rats are genetically predisposed to a high incidence of tumors and cancers. Some tumors may be malignant while others are benign. In all cases, however, it is advisable to remove the tumor to help reduce the fatalities as a result of the cancerous growths.

Symptoms and Types


  • Benign tumors of the skin that develop in the chest, back or tail.

Mammary Fibroadenomas

  • The most common kind of reproductive tumors in rats.
  • Can be found in the mammary (breast) tissue, and are usually benign (not malignant).
  • Found in both female and male rats.

Mammary Adenocarcinomas

  • 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.
  • Typically these tumors are soft, round, or somewhat flat growths that can be moved

Pituitary Gland Tumors

  • Common in female rats.
  • Due to the position of the tumor, symptoms include head tilting and depression.
  • These tumors usually lead to sudden death

Testicular Tumors

  • Found in the testes of male rats

Zymbal’s tumors

  • Found at the base of the ear in older rats; they are relatively infrequent


Rats by nature are very susceptible to the development of tumors. Some are more common than others, of course. For example, mammary adenocarcinomas are common in rats because of their widely distributed mammary tissue. Tumors of the pituitary gland increase in occurrence in relation to increased consumption of high-calorie foods.


Tumors growths that can be seen or felt externally are the easiest to diagnose. Tumors that occur in the internal organs can only be diagnosed wih the assistance of X-rays and other scans.


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.

Living and Management

While recovering from surgery for a tumor, your rat will require appropriate care to avoid complications. Consult your veterinarian regarding care, management, and diet during this postoperative period.

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