The Great Impostors - Mast Cell Tumours
Mast
Cell Tumours it is believed are one of the most commonly found skin tumours in
the canine although it is thought to be very rare in cats. Certain breeds
appear to be more susceptible as do females. It is very rare to find tumours of
this sort in dogs under the age of a year old, and again rare in dogs aged over
10 years. Mast Cell tumours are extremely difficult to treat successfully due
to the variety of their appearance and biological behaviour.
Mast
Cell Tumours are found in the loose connective tissues. The purpose of
connective tissue is to connect and support other tissues and organs. The Mast
cells play an important role in the body’s immune response and contain several
kinds of chemicals, one of which prevents blood from clotting in the blood
vessels (heparin), the other 2 act to dilate or widen small blood vessels
(histamine & serotonin). These chemicals are vital to the normal bodily
function, however they are extremely damaging when released in excess.
There are 2 different forms of Mast Cell Tumours on the skin, the most common
being a mass of between 1 and 10 cm in diameter which is well formed, raised and
hard to the touch, it can also appear reddened and almost “wet” looking. The
surrounding area of the Tumour may have a blister like appearance and the centre
may be yellow in colour and look ulcerated. The other is poorly formed, usually
has hair on it and is not reddened or ulcerated however it can also resemble
both types. If the lump is massaged or rubbed it may swell or form “hives”
these are known as the Darier sign. These “hives” are caused by a realise of
histamine from the mast cells themselves. The Mast Cell Tumour does posses one
characteristic and that is a tendency for them to change in size even on a day
to day basis, getting bigger or smaller on a whim.
No
one really understands what causes cancer although they are many “suggestions”
that Mast Cell Tumour development may be related to coat colour i.e. Golden and
red coats being more susceptible, dogs with allergies and/or other inflammatory
conditions may also be more at risk, however there is no way of preventing the
cancer the best one can do is to keep a check of the overall health of any
pets. The most likely sign of one is obviously the finding of a tumour of some
description, Mast Cell Tumours can appear singularly or in groups and can appear
anywhere on the body, they are unlikely to be pain-full unless severely swollen
or ulcerated and there has been some observation that the more ulcerated the
tumour the higher grade it is likely to be.
The most common way to treat
Mast Cell Tumours is surgically, although radiation and chemotherapy are also
used. Surgery is a first choice treatment however because the tumours are
invasive it is necessary to remove a wide margin around the tumour of about 3cm
to make sure that all stray cancerous cells are captured. Once removed the
tumour is then submitted for a histology to find out what grade it is and also
whether all the cells have been captured, a clean margin. Mast Cell Tumours
themselves are unique in there ability to form as multiple primary tumours at
times, they are also unpredictable in their behaviour, because of this it is
always advised to “grade” the tumour. By grading the tumour it is possible to
determine the degree at which the malignant mast cells differ from the normal
mast cells, tumour behaviour, tumour recurrence and long term prognosis /
survival. Grades are given on a scale of 1 – 3 with one being the least likely
to re occur and 3 being the most likely to re occur. A grade 1 or grade 2
tumour that has been completely removed and has a clean margin will usually
require no other immediate therapy other than monitoring the animal for 18 – 24
months before being reasonably confident that the problem has been resolved.
Grade 3 tumours however will need subsequent treatment in the form of radiation
therapy or in the case where there is not a clean margin further surgery. It is
important to note here that if radiotherapy or chemotherapy are used these
treatments have no effect on the spread of the tumour they are a local treatment
only. Radiation is sometimes used instead of surgery, not to remove the tumour
but to shrink it especially if the tumour is in a place where removal is
difficult. Sometimes the only form of treatment is supportive care intended not
to extend the dogs life but to make it as comfortable and enjoyable as possible.
It
is wise to know that some dogs who have had surgical removal of a Mast Cell
Tumour will develop more, and 50 % will re-grow in the same area, the biggest
risk from Mast Cell Tumours is from the secondary cancers. Mast Cell Tumours
often spread to the Lymph nodes, Spleen and the Bone Marrow; any future lumps
must be evaluated as quickly as possible. Mast Cell Tumours have not been shown
to be genetically transmitted, and evidence remains lacking for a viral cause.
Mast
Cell Tumours occur frequently in dogs, although they are well documented and
indeed understood they are the most unpredictable in behaviour and appearance.
No one knows what causes Mast Cell Cancer or how to be certain that it has been
cured. As owners the best we can do is to be vigilant and attentive to the
general health of our dogs, and make sure that any lumps and bumps are examined
carefully as soon as they are spotted in order to catch a Mast Cell Tumour in
it’s early stages. Mast Cell Tumours can be lethal if not acted upon quickly.