Etiology

Mast cells play an important role in the body’s immune surveillance system. When confronted with allergens they release granules containing histamine, heparin, and in the rat and mouse, serotonin. These chemicals respond by setting up an allergic response attracting additional immune surveillance cells to the site. This leads to the inflammation and swelling that is observed with allergies. Sometimes for unknown reasons mast cells begin to grow out of control. The result is a mast cell tumor, or if mast cell proliferation is systemic is known as mastocytosis. Mast cell tumor growth may arise as a single nodule in the skin, or there may be more growths in other areas or organs of the body.

Mast cell tumors are sometimes called the great pretender since its appearance can mimic that of a lipoma , cyst, or a histiocytoma. Mast cell tumors may progress from benign tumors to tumors that are metastatic. Since it is often impossible to determine just by appearance if the tumor is benign, the recommended treatment is to have the tumor surgically removed. The prognosis is good in early detection and tumor removal.

Some factors thought to be involved in mast cell tumor formation include heredity, viral infections, chronic inflammation, or environmental factors. As with many cancers, mast cell tumors tend to be associated with older animals.

Photo and case history of mast cell tumor have been provided in the following figure:

• Fig. 1: Mast cell tumor in 2 year old male rat.

Diagnostics

X-ray or ultrasonography (if available) to determine hepatomegaly ( liver enlargement), splenomegaly (enlargement of spleen), or lymph node involvement

Fine needle aspirate (FNA) for cytology.

Lab test: CBC (complete blood count) to check for low platelet count, low red blood cell count, low white blood cell count, and elevated mast cell count to rule out the spread of the tumor. WBC (white blood cell count) may be elevated if there are circulating inflammatory compounds, or if gastrointenstinal ulceration is present.

Histopathologic examination of excised tumor.

Treatment

An antihistamine such as benadryl may be used prior to surgery, or in the event surgery is not an option, to reduce the effects of histamine release and give comfort.

Rats do experience pain with surgical procedures. The type of pain medication used post-op should be determined based on extent of procedure and the anticipated severity of pain.

For severe pain or first 24 hours post-op: butorphanol (Torbugesic).

For mild to moderate pain: Banamine (flunixin meglumine) or carprofen. Do not use if a corticosteroid has already been prescribed.

A corticosteroid (e.g., prednisone/prednisolone) may be used to reduce tumor size, or associated inflammation, if surgery is not an option. However, it is important to keep in mind that the use of a corticosteroid will not eliminate the tumor itself.

If tumor(s) are metastatic, and stomach ulceration is thought to be a concern, H2 antihistmines such as cimetidine or ranitidine may be recommended.

For information regarding medications refer to the Rat Medication Guide.

Nursing Care

Provide additional nutritional supplement , such as soy baby formula, Ensure, Boost, NutriCal paste (for dogs and cats found in pet store), mashed avocado, and baby foods during recuperation. Include additional multi-vitamin supplement (can be found in pet store) if food intake is poor.

Encourage fluid intake while recuperating, such as water, Jello water , or electrolyte replacement drinks such as Pedialyte or Gatorade (which can be found in local grocery stores). Please note that Pedialyte is only good refrigerated for 24 hours after opened, but can be frozen as ice cubes and thawed as needed.
*Note: a juicy type of fruit also provides an additional fluid source in the diet.

Outcome

Prevention

References

Posted on September 15, 2003, 21:45, Last updated on June 16, 2008, 13:30 | Neoplasia