Jessie is a beautiful bouncy 5 year female desexed boxer. Unfortunately Jessie has had a history of skin lesions called Mast Cell Tumours which are a form of cancer (often seen in the skin but can also be found within organs and spread throughout the body).
Mast cell tumours probably account for approximately 1 in 5 of the skin tumours that we see. Boxers are at an especially high risk (and other breeds such as English bulldogs, boston terriers, sharpeis, Labradors, golden retrievers, schnauzer and cocker spaniels). However, any dog can develop one!
Often because they are seen in the skin – they can be lesions that arise suddenly, are ulcerated, itchy or bother your pet, but sometimes they do not have any of the above symptoms.
Lumps should be investigated ideally as soon as they are noticed – and often a ‘fine needle aspirate or FNA’ is performed. In doing so, a needle is inserted in the lump and cells from that area are sampled and examined under a microscope. This can tell us what type of cells are present in the lump and by looking at whether there is uniform shape and size, whether it is likely to require removal via surgery or not.
The mast cells and their granules have distinct staining characteristics leading to their recognition. However, it is important to note that grading a tumour cannot happen by this FNA technique and instead the entire mass should be removed surgically with margins and sent for grading by a histopathologist.
Tumors that have been present for months or years tend to be more benign.
Grading the Mast Cell Tumor
The pathologist will most likely use the Patnaik system for grading the mast cell tumour when the biopsy sample is read. The grade is a reflection of the malignant characteristics of the cells under the microscope (which generally correlates to the behaviour of the tumour) with Grade I being benign, Grade III being malignant, and Grade II having some ability to go either way.
GRADE I TUMORS
This is the best type of mast cell tumour to have. While it may tend to be larger and more locally invasive than may be visually apparent, it tends not to spread beyond its place in the skin. Surgery should be curative. If the original biopsy shows that the tumour has only narrowly been removed or that the tumour extends to the margins of the sample, a second surgery should promptly be done to get the rest of the tumor, if at all possible. If the grade I mast cell tumor is incompletely excised it will grow back in time; it is best to get it all and be done with it as quickly as possible. About half of all mast cell tumors are Grade 1 tumors and can be cured with surgery alone.
GRADE II TUMORS
This type of tumor is somewhat unpredictable in its behavior. Recent studies have shown that radiation therapy administered to the site of the tumor can cure greater than 80% of patients as long as the tumor has not already shown distant spread.
GRADE III TUMORS
This is the worst type of mast cell tumor to have. Grade III tumors account for approximately 25% of all mast cell tumors and they behave very invasively and aggressively. If only surgical excision is attempted without supplementary chemotherapy, a mean survival time of 18 weeks (4-5 months) can be expected.
Other testing features can be applied to the sample but, in general, the grade, stage, location and symptoms of the patient help point to therapy.
Therapy for mast cell tumours consists of surgery, radiation therapy, and chemotherapy (as is the case for almost all types of cancer). What combination of the above is chosen depends on the extent of spread and malignant characteristics of the tumor.
If the tumour can be cured with one or even two surgeries, this is ideal. Mast cell tumours are highly invasive, and very deep and extensive margins - at least 2 cm in all directions - are needed. This can be a problem for tumours located on the neck or in the mouth. Further, the inflammation associated manipulating the tumour can lead to extra swelling, bleeding, and even a drop in blood pressure. In one study, a 10% incidence of wound healing failure (dehiscence) was observed with mast cell tumours.
The biopsy sample will not only yield the grade of the tumour but will include a measurement of the tissue margin (the width of normal tissue that has been excised around the tumour). The width of the margins will go far in determining if further treatment is needed. If the margins are narrow or margins indicate there is still tumour left behind then a second surgery or even a course of radiation therapy may be desirable. Clean margins are generally defined as a 10 mm margin around the tumour in all directions. If the margin is clean, theoretically the tumour should be completely removed but it is still a good idea to keep an eye on the area over the years.
Luckily the mast cell tumours that have been removed previously have been grade 1 tumours, and both lumps removed this time have been grade 1 as well. This is positive news, but it does mean that every lump or bump that is found on Jessie will need to be investigated immediately.
As disfiguring as surgical excisions (removals) can be, the outcome of a complete excision of a low grade tumour (which can be curative) is much more promising than allowing a tumour to develop and spread to other organs.