Mastocytoma

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A Mastocytoma is an accumulation or nodule of mast cells that resembles a tumor. In many animals 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. Up to 20 to 25 percent of skin tumors in dogs are mast cell tumors,[1] with a similar number in cats.[2]

Mast cell tumor of the paw
Mast cell tumor on the lip

Commonly affected breeds

Symptoms

Mast cell tumors are known amongst veterinary oncologists as 'the great pretenders' because their appearance can be varied, from a wart-like nodule to a soft subcutaneous lump (similar on palpation to a benign lipoma) to an ulcerated skin mass. 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[5] (especially in Boxers and Pugs)[4].

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 (present in up to 25 percent of cases)[4], or disseminated intravascular coagulation.

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. The granules of the mast cell stain blue to dark purple with a Romanowsky stain, and the cells are medium sized.[6] 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.

  • Grade I - well differentiated and mature cells with a low potential for metastasis
  • Grade II - intermediately differentiated cells with potential for local invasion and moderate metastatic behavior
  • Grade III - undifferentiated, immature cells with a high potential for metastasis[1]

However, there is a significant amount of discordance between veterinary pathologists in assigning grades to mast cell tumors due to imprecise criteria.[7]

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[3]

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

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.[5]

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.[8] 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.[3] Multiple tumors that are treated similarly to solitary tumors do not seem to have a worse prognosis.[9]

Mast cell tumors do not necessarily follow the histological prognosis. Further prognostic information can be provided by AgNOR stain of histological or cytological specimen. [10] Even then there is a risk of unpredictable behaviour.

Mast cell tumors in cats

Two types of mast cell tumors have been identified in cats, a mast cell type similar to dogs and a histiocytic type that may resolve spontaneously. Young Siamese cats are at an increased risk for the histiocytic type,[2] although the mast cell type is the most common in all cats and is considered to be benign when confined to the skin.[4] Tumors of the skin are usually located on the head or trunk.[11] Gastrointestinal and splenic involvement is more common in cats; 50 percent of cases in cats primarily involved the spleen or intestines.[12] Gastrointestinal mast cell tumors are most commonly found in the muscularis layer of the small intestine but can also be found in the large intestine.[13] Diagnosis and treatment are similar to the dog. Cases involving difficult to remove or multiple tumors have responded well to strontium-90 radiotherapy as an alternative to surgery.[14] The prognosis for solitary skin tumors is good, but guarded for tumors in other organs. Histological grading of tumors has little bearing on prognosis.[15]

Mast cell tumors in other animals

Mast cell tumors are an uncommon occurence in horses. They usually occur as benign, solitary masses on the skin of the head, neck, trunks, and legs. Mineralization of the tumor is common.[16] In pigs and cattle mast cell tumors are rare. They tend to be solitary and benign in pigs and multiple and malignant in cattle.[4] Mast cell tumors are found in the skin of cattle most commonly, but these may be metastases from tumors of the viscera.[17] Other sites in cattle include the spleen, muscle, gastrointestinal tract, omentum, and uterus.[18]

References

  1. ^ a b Brière C (2002). "Use of a reverse saphenous skin flap for the excision of a grade II mast cell tumor on the hind limb of a dog". Can Vet J. 43 (8): 620–2. PMID 12170840.
  2. ^ a b Johnson T, Schulman F, Lipscomb T, Yantis L (2002). "Histopathology and biologic behavior of pleomorphic cutaneous mast cell tumors in fifteen cats". Vet Pathol. 39 (4): 452–7. PMID 12126148.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  3. ^ a b c Morrison, Wallace B. (1998). Cancer in Dogs and Cats (1st ed. ed.). Williams and Wilkins. ISBN 0-683-06105-4. {{cite book}}: |edition= has extra text (help)
  4. ^ a b c d e "Cutaneous Mast Cell Tumors". The Merck Veterinary Manual. 2006. Retrieved 2007-01-27.
  5. ^ 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 2006-08-19.
  6. ^ "Common Cytology Results". The Merck Veterinary Manual. 2006. Retrieved 2007-01-27.
  7. ^ Strefezzi R, Xavier J, Catão-Dias J (2003). "Morphometry of canine cutaneous mast cell tumors". Vet Pathol. 40 (3): 268–75. PMID 12724567.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  8. ^ Sfiligoi G, Rassnick K, Scarlett J, Northrup N, Gieger T (2005). "Outcome of dogs with mast cell tumors in the inguinal or perineal region versus other cutaneous locations: 124 cases (1990-2001)". J Am Vet Med Assoc. 226 (8): 1368–74. PMID 15844431.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  9. ^ Mullins M, Dernell W, Withrow S, Ehrhart E, Thamm D, Lana S (2006). "Evaluation of prognostic factors associated with outcome in dogs with multiple cutaneous mast cell tumors treated with surgery with and without adjuvant treatment: 54 cases (1998-2004)". J Am Vet Med Assoc. 228 (1): 91–5. PMID 16426175.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  10. ^ Scase T, Edwards D, Miller J, Henley W, Smith K, Blunden A, Murphy S. "Canine mast cell tumors: correlation of apoptosis and proliferation markers with prognosis". J Vet Intern Med. 20 (1): 151–8. PMID 16496935.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  11. ^ Litster A, Sorenmo K (2006). "Characterisation of the signalment, clinical and survival characteristics of 41 cats with mast cell neoplasia". J Feline Med Surg. 8 (3): 177–83. PMID 16476559.
  12. ^ Takahashi T, Kadosawa T, Nagase M, Matsunaga S, Mochizuki M, Nishimura R, Sasaki N (2000). "Visceral mast cell tumors in dogs: 10 cases (1982-1997)". J Am Vet Med Assoc. 216 (2): 222–6. PMID 10649758.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  13. ^ "Gastrointestinal Neoplasia". The Merck Veterinary Manual. 2006. Retrieved 2007-01-27.
  14. ^ Turrel J, Farrelly J, Page R, McEntee M (2006). "Evaluation of strontium 90 irradiation in treatment of cutaneous mast cell tumors in cats: 35 cases (1992-2002)". J Am Vet Med Assoc. 228 (6): 898–901. PMID 16536702.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  15. ^ Molander-McCrary H, Henry C, Potter K, Tyler J, Buss M. "Cutaneous mast cell tumors in cats: 32 cases (1991-1994)". J Am Anim Hosp Assoc. 34 (4): 281–4. PMID 9657159.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  16. ^ Cole R, Chesen A, Pool R, Watkins J. "Imaging diagnosis--equine mast cell tumor". Vet Radiol Ultrasound. 48 (1): 32–4. PMID 17236357.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  17. ^ Smith B, Phillips L (2001). "Congenital mastocytomas in a Holstein calf". Can Vet J. 42 (8): 635–7. PMID 11519274.
  18. ^ Ames T, O'Leary T (1984). "Mastocytoma in a cow: a case report". Can J Comp Med. 48 (1): 115–7. PMID 6424914.

External link

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