Mastocytoma

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A Mastocytoma is an accumulation or nodule of mast cells that resembles a tumor. In dogs and cats this collection of mast cells is actually a mast cell tumor. A mast cell originates from the bone marrow and is normally found throughout the connective tissue of the body. It is associated with allergic reactions because it releases histamine. A mast cell tumor is a common malignant tumor of the skin in older dogs and cats.

Mast cell tumor of the paw

Mast cell tumor on the lip

1 Commonly affected breeds
2 Symptoms
3 Diagnosis
4 Treatment and prognosis
5 Mast cell tumors in cats
6 References

[edit] Commonly affected breeds

[edit] Symptoms

Mast cell tumors are known amongst veterinary oncologists as 'the great pretenders' because their appearance can be very varied. From a wart-like nodule to a soft subcuatneous lump identical on palpation to a benign lipoma to an ulcerated skin mass. Therefore all lumps should be checked by fine needle aspiration: palpation or visual inspection is never adequate. Most mast cell tumors are small, raised lumps on the skin. They may be hairless, ulcerated, or itchy. They are usually solitary, but in about 6 percent of cases there are multiple mast cell tumors.^[2] Manipulation of the tumor may result in redness and swelling from release of mast cell granules, also known as Darier's sign. In rare cases a highly malignant tumor is present, and symptoms may include loss of appetite, vomiting, diarrhea, and anemia. The presence of these symptoms usually indicates mastocytosis, which is the spread of mast cells throughout the body. Release of a large amount of histamine at one time can result in ulceration of the stomach and duodenum, or disseminated intravascular coagulation.

[edit] Diagnosis

Mast cell tumor cytology

A needle aspiration biopsy of the tumor will show a large number of mast cells. This is sufficient to make the diagnosis of a mast cell tumor. However, a surgical biopsy is required to find the grade of the tumor. The grade depends on how well the mast cells are differentiated, from grade I to grade III. The disease is also staged.

Stage I - a single skin tumor with no spread to lymph nodes
Stage II - a single skin tumor with spread to lymph nodes in the surrounding area
Stage III - multiple skin tumors or a large tumor invading deep to the skin with or without lymph node involvement
Stage IV - a tumor with metastasis to the spleen, liver, bone marrow, or with the presence of mast cells in the blood^[1]

X-rays, ultrasound, or lymph node, bone marrow, or organ biopsies may be necessary to stage the disease.

[edit] Treatment and prognosis

Removal of the mast cell tumor through surgery is the treatment of choice. Antihistamines such as diphenhydramine are given prior to surgery to protect against the effects of histamine released from the tumor. Wide margins (two to three centimeters) are required because of the tendency for the tumor cells to be spread out around the tumor. If complete removal is not possible due to the size or location, additional treatment such as radiation therapy or chemotherapy may be necessary. Prednisone is often used to shrink the remaining tumor portion. H2 blockers such as cimetidine protect against stomach damage from histamine. Vinblastine and CCNU are common chemotherapy agents used to treat mast cell tumors.^[2]

Mast cell tumors that are grade I or II that can be completely removed have a good prognosis. Any mast cell tumor found in the gastrointestinal tract, paw, or on the muzzle has a guarded prognosis. Previous beliefs that tumors in the groin or perineum carried a worse prognosis have been discounted.^[3] Tumors that have spread to the lymph nodes or other parts of the body have a poor prognosis. Any dog showing symptoms of mastocytosis or with a grade III tumor has a poor prognosis. Boxers have a better than average prognosis because of the relatively benign behavior of their mast cell tumors.^[1] Mast cell tumors do not necessarily follow the histological prognosis. Further prognostic information can be provided by AgNOR stain of histological or cytological specimen. Even then there is a risk of unpredictable behaviour.

[edit] Mast cell tumors in cats

Siamese cats are at an increased risk for mast cell tumors.^[1] Gastrointestinal and splenic involvement is more common in cats; 50 percent of cases in cats primarily involved the spleen or intestines.^[4] Diagnosis and treatment are similar to the dog. The prognosis for solitary skin tumors is good, but guarded for tumors in other organs.

[edit] References

^ ^a ^b ^c ^d Morrison, Wallace B. (1998). Cancer in Dogs and Cats, 1st ed., Williams and Wilkins. ISBN 0-683-06105-4.
^ ^a ^b Moore, Anthony S. (2005). Cutaneous Mast Cell Tumors in Dogs. Proceedings of the 30th World Congress of the World Small Animal Veterinary Association. Retrieved on 2006-08-19.
^ Sfiligoi, Gabriella, et al. (2005). "Outcome of dogs with mast cell tumors in the inguinal or perineal region versus other cutaneous locations: 124 cases (1990–2001)". Journal of the American Veterinary Medical Association 226 (8): 1368-1374. Retrieved on 2006-08-19.
^ Takahashi, Tomoko, et al. (2000). "Visceral mast cell tumors in dogs: 10 cases (1982–1997)". Journal of the American Veterinary Medical Association 216 (2): 222-226. Retrieved on 2006-08-19.