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The causes symptoms diagnosis and treatment of mast cell tumors mct in dogs and cats

Clinical and pathological effects Mast cells are part of the immune system. They are produced in bone marrow. When mature, they are found in blood vessels where they become activated by antibodies or local tissue damage, chemicals or heat.

Once activated, they release a variety of biologically active chemicals that cause local inflammation the best known being histamineand that attract other types of immune system cells to the site.

Mast cell tumours MCT are among the commonest neoplasms clusters of cells caused by abnormal growth of dogs. These cancerous growths can be solitary masses of cells that are benign ie unlikely to spread or they can be malignant and likely to spread to other parts of the body via the lymphatic or blood systems. There are also several types of the systemic form of the disease — in which the disease is found throughout the body- and these have been defined by the type of mast cells involved and the sites at which they occur Marconato et al 2008, Valent 2010.

In mastocytosis, for example, MCTs appear throughout the body and large numbers of mast cells are found in the bone marrow. When neoplastic mast cells begin to circulate in the blood this form then becomes a type of leukaemia. Here though we focus on the common form of the disease characterised by solitary or multiple MCT masses. The appearance of cutaneous skin MCTs is very variable.

It can be similar to various other types of skin neoplasia. Conversely, some growths initially thought to be benign cysts or lipomas benign tumours of fatsometimes turn out to be MCTs which may be malignant Nuttall et al 2009. Tumours occur as a result of genetic mutations that result in abnormal growth of the affected cells.

A gene, c-KIT, is known to be involved in some, but not all, canine mast cell tumours London et al 1990. It influences receptors in the cell that bind with growth promoting substances and when present in its mutated form has the effect of causing affected cells to continuously divide resulting in the growth of the neoplasm.

Diagnosis & Management of Canine Mast Cell Tumors

The c-KIT gene therefore predisposes animals to develop malignant mast cell tumours, and dogs with this gene are more likely to die due to MCT Zemke et al 2002, Webster et al 2006.

Another mutation can affect the platelet derived growth factor receptor PDGFRwhich is involved in the blood supply to growing tumours. Both this and the receptor affected by the c-KIT gene contain the protein, tyrosine kinase TKand are affected by some modern drug treatments tyrosine kinase inhibitors - TKIs that can be somewhat effective against cancers caused by these mutations in humans and dogs Blackwood 2010. As well as causing disease in the same way as any other cancer — by causing organ damage and dysfunction, pain, debilitation and appetite reduction; the adverse effects of MCTs are also caused by the uncontrolled release of the biologically active chemicals that these cells produce.

Canine Mast Cell Tumors

Locally, there is often inflammation around the tumour mass with redness, oedema fluid in the tissueand pain. Wound healing in these areas may be delayed: Occasionally anaphylaxis, a systemic allergic response — in which the whole body is affected, may occur in dogs with mast cell tumours.

Affected dogs may collapse with a failing circulation, breathing difficulties caused by swelling of tissues and fluid release into the lungs, vomiting and diarrhoea.

Mast Cell Tumors in Dogs and Cats | Canine and Feline MCT

The blood clotting mechanism can also sometimes be affected in dogs with MCTs. More commonly, affected animals develop gastrointestinal disease, especially ulceration, as a result of histamine release by the tumour. Solitary MCTs vary from the benign to the aggressively malignant. This appears to be influenced partly by the site of the tumour.

For example, those around muco-cutaneous junctions where skin meets moist, mucous membranes eg the lips and in the groin of male dogs tend to be more malignant. MCTs are graded clinically according to the following scheme Owen 1980which may be helpful in prognosis predicting how the disease may develop and when making decisions making regarding treatments: One small tumour confined to the skin, no lymph node involvement One small tumour confined to the skin with local or regional lymph node involvement Multiple skin tumours or a large infiltrating tumour with or without regional lymph node involvement IV Any tumour with distant metastases spread of the tumour to other parts of the body Tumours are also graded either I, II or III according to their cellular characteristics.

This grading, based on the microscopic appearance of biopsy specimens, is also useful to aid decision making for treatment and to guide prognosis Patnaik et al 1984. Grade I masses and the low malignancy grade II tumours are likely to be cured just by surgery. Chemotherapeutic agents TKIs can be useful in the treatment of the higher-grade tumours perhaps especially in c-KIT positive animals.

Such agents may prolong life rather than achieving a complete cure Hahn et al 2008, Blackwood 2010. The mean age at which Boxers are diagnosed with MCTs is around 8 years but these tumours can occur at any age, even in puppies Nuttall et al 2009.

Return to top 2. Intensity of welfare impact The effects of mast cell tumours on welfare depend on the malignancy and the site of the tumour. They can be a result of both the mechanical effects of the tumour s eg due to it compressing or compromising the movement of surrounding tissues and of the effects of histamine and the other biologically active substances produced by the tumour cells. These chemicals make the skin in the area inflamed and itchy or painful, and can cause gastrointestinal ulceration with associated pain.

Spread of the tumour to internal organs can stop them functioning properly and cause pain. Although the lower grade forms of the disease may be completely cured, death is a common outcome for the more malignant forms and it has been reported that, despite treatment, around half of dogs with high grade tumours die within a year Murphy et al 2004. Recently developed drugs may prove more effective London et al 2009, Blackwood 2010, Robat et al 2010. Return to top 3. Duration of welfare impact The average median age of diagnosis of mast cell tumour is 8.

The duration of the period when welfare is compromised depends on the malignancy, form and site of the tumour. Mast cell tumours causing solitary masses on the skin may affect welfare for only a relatively short period of a few weeks if the MCT is successfully treated. If not treated successfully, the MCT is likely to cause increasing discomfort, pain, distress and ultimately, death.

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Canine mast cell tumors: diagnosis, treatment, and prognosis

Number of animals affected Boxers have a greater predisposition to neoplasia than many other breeds of dogs Cohen et al 1974. UK VetCompass data for dogs overall, showed that 3. Return to top 5. Diagnosis MCTs cannot be diagnosed by visual examination: Diagnosis is usually made by collecting cells for examination by inserting a needle into the tumour and removing cells and fluid with a syringe for microscopic examination Baker-Gabb et al 2003.

It is possible and desirable to check the likely suitability of treatment of the tumour by TKI chemotherapy Blackwood 2010. Return to top 6.

  1. Some MCT can have a more benign-type of behavior where the tumor is present for months to years without change in size or a more aggressive behavior where growth occurs rapidly. Biologic behavior and prognostic factors for mast cell tumors of the canine muzzle.
  2. Feline mast cell tumors of the skin tend to have a more benign nature as compared to mast cell tumors in dogs and can often be cured with complete tumor removal. Prognosis The prognosis for MCT depends upon the tumor grade, whether surgery has resulted in complete tumor removal, and whether the MCT has spread or not.
  3. The behavior of mast cell tumors reflects their grade a term used by pathologists and oncologists to describe such things as how-well differentiated a tumor is, how frequently it is dividing, how invasive to adjacent structures, and other criteria.
  4. Mucocutaneous location In limited published cases, eyelid margin MCTs appeared to have relatively benign behavior and were effectively treated with local therapy, although one dog was reported to have regional lymph node LN metastasis. Additionally, it would be beneficial to know how the currently recommended lower dose of toceranib phosphate will work in combination.

There has been some research into the genetic causes of MCTs but the genes involved have not been determined Munday et al 2009 and there are no published studies regarding the degree of heritability or the pattern of inheritance.

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Signs & Symptoms

How do you know if an animal is a carrier or likely to become affected? There is no way to predict which individuals will be affected and it is not known if carriers can exist, that can pass the risk of the disease on to offspring without ever developing the disease themselves.

Return to top 8. Tackling this disease by selective breeding is, at present, complicated by the fact that these tumours often develop after breeding age Nuttall et al 2009. More rapid progress would be possible if it there was a way to detect the genes responsible for the condition.

Return to top 9. Return to top 10. Australian Veterinary Journal 81: Veterinary Radiology and Ultrasound 43: Journal of Small Animal Practice 43: Journal of Small Animal Practice 48: Cancer morbidity in dogs and cats from Alameda County.

Genetic Welfare Problems of Companion Animals

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Journal of the American Animal Hospital Association 38: