1st May 2006

Could you give me any information on mast stem tumours?

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Question:

Could you give me any information on mast stem tumours? I am also having trouble understanding the biopsy report on my Rottweiler/Staffordshire cross, so any pointers as to how to read it would also be helpful.

Answer:

I suspect the tumour type you are referring to is actually called a mast cell tumour (MCT). MCT's represent up to 20% of all skin tumours in dogs. Boxer dogs appear to be most prone to the tumour but all short-nosed breeds appear to have a predisposition to developing this tumour. There is no typical appearance of an MCT: they can appear as discrete single lumps on the skin or ill-defined swelling under the skin surface. Unfortunately, they do have a high incidence of spread and it is not unknown for an MCT that has been slow-growing and benign to suddenly change into an aggressive, rapid-spreading variety. It is imperative that any MCT should be treated with careful respect. For a single mass, surgical excision with wide margins of at least 2-3 cm around the lump is the treatment of choice. If there is evidence of spread, to local lymph nodes for example, surgery and possibly radiation therapy plus chemotherapy should be considered. For a solitary MCT with no evidence of it having spread, surgery can certainly be curative. If there is evidence of spread of the MCT then prognosis for a complete cure is much reduced. The biopsy report may 'stage' the tumour; often a four-grade system is used. A grade 1 is a tumour that shows no evidence of having spread. A grade 4 is a mass that has spread to distant parts of the body or has recurred at a site from which it had been previously occurred. The staging of MCT's is a clinical judgement that your vet will be in the best position to discuss with you.