What is a mast cell tumour?

Mast cell tumours are the most common skin tumours in the dog accounting for over 20% of all malignant skin tumours. Mainly they occur in older dogs, with an average age from 7 to 9 years old although sometimes dogs under a year of age can also be affected. There is no sex predisposition but among various breeds the Boxer is one of the most frequently affected, followed by the Labrador, Golden Retriever, Sharpei and Weimaraner.

These tumours appear as an isolated mass of various sizes, generally like a firm nodule raging from few millimitres to several centimetres, the skin overlying it can be alopecic or eritematous or in few cases even ulcerated. Ulceration is often a sign of more aggressive behaviour.

Palpation of these masses can sometimes cause a release of histamine, a molecule contained within the granules that characterise the cells of this type of tumour and this could potentially cause signs such as swelling or redness.

Location of these masses varies from the trunk, in most of the cases, followed by hind limbs and in fewer occasions the head. You can see pictures of a variety of locations here.

These tumours can spread, therefore the regional lymph nodes should be examined as well as the spleen and liver.

Various substances are produced by these tumours and vomiting or blood in the faeces may be seen. Moreover any wound resulting from a surgical excision of a mast cell tumour should be strictly monitored as risk of wound breakdown is a common sequela.

The diagnosis is made by clinical appearance together with cytological and/or histological findings. Samples are routinely sent for laboratory analysis. Cytology often carried out by a fine needle aspiration can be as high as 90% diagnostic, although this tool does not tell us the grade of malignancy, for which histology is required.

The most common system of grading a mast cell tumour divides them into three classes, Grade I, with a benign behaviour, grade II called intermediate grade, that could potentially behave as grade I or as grade III, and grade III malignant. Despite all, any mast cell tumour should be considered as a potential malignancy as the rate of recurrence post surgery is high.

Complete excision is curative and the treatment of choice for grade I mast cell tumours, with at least two centimetre margins of excision around the perimeter of the mass. If the margins are not clear following surgery a revision surgery is required, or if not possible a follow up with radiotherapy should be provided to decrease the chances of recurrence.

Chemotherapy is also an option and there are various protocols available but are mainly referred to the more malignant ones, and mainly for the grade three mast cell tumours.

Our specialist soft tissue surgeons are highly experienced in dealing with mast cell tumours in dogs. For the best for your pet, ask your vet to refer you to Northwest Surgeons.