Tumors

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Both mice and rats are very susceptible to formation of tumors.

Rats over 2 years of age are reported to have an 87% chance of

developing one or more types of tumors.



Mice frequently develop tumors representing a wide variety of

tissue types.  The tumors may be external or internal.  Leukemia

(cancer involving the white blood cells) is quite common in mice

as well.



Both male and female rats develop benign mammary (breast) tumors,

and females develop benign tumors of the uterine and vaginal

linings.  These are the most common tumors of pet rats.  Because

rats have mammary tissue in locations beneath the skin other than

along the underside of the belly, it is not uncommon to find

lumps and bumps representing mammary tumors over the shoulders,

flanks and base of the tail.  These tumors are relatively easy to

surgically remove under general anesthesia.



Owners of pet mice and rats should seek veterinary attention at

once after discovering a lump, bump or unusual mass protruding

from a body opening.  The mass can be surgically removed by the

veterinarian and biopsied to determine its exact identity (tissue

type, benign vs malignant, etc.) which, in turn, helps to

determine the long-term outlook for the patient.  Tumors tend to

grow continuously larger and may ulcerate and become infected if

they reach very large size.  For this reason, it is always

preferable to remove them when they are small.