With
breast cancer awareness at an all time high, it is important
to know that breast cancer doesn’t just affect humans.
Dogs can also get mammary (breast) cancer. In fact it is even
more common in dogs than in humans. Female dogs are much more
likely to be affected but it can also occur, albeit rarely,
in male dogs.
Studies
indicate that the incidence rate of mammary tumours
in older entire (unspayed) female dogs is about 1 in
4 (25%). But with early detection, treatment can often
be successful. Also, mammary tumours in female dogs
are almost always preventable. So it is important to
know what to do to prevent mammary tumours in dogs,
to check your dog regularly for the presence of mammary
tumours and to know what to expect if you discover anything
different to the norm.
A dog’s mammary glands run from chest to groin
on the underside of their body either side of the mid
line. Each mammary gland has a nipple, each dog typically
having 8, although this can vary. |
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Tumours
in the mammary glands can often be discovered by gently
feeling the area for any lumps or irregularities. Lumps
may be felt anywhere along the mammary chain. Tumours can
be slow or fast growing masses under the skin around the
nipple area, in single lumps or multiples, showing as solid
masses or swellings. Mammary lumps may be fixed or moving.
Inflammatory carcinomas can present like mastitis so look
for heat or swelling.
Some dogs and even some dog breeds can be predisposed to
cancer of the mammary glands. Causes are unknown but hormones
are thought to play a part in mammary cancers.
Mammary tumours are more common in older female dogs with
the average age of affected dogs being 10 years old. Not
all mammary tumours are cancerous. About 50% of dog mammary
tumours are benign with the other 50% being malignant. Both
benign and malignant tumours grow and can become ulcerated
and painful. It is often noted that benign tumours tend
to be multiples, smooth and slower growing than the more
aggressive irregular single growths often seen in mammary
cancers, but this is a guide only and not a diagnostic tool.
The presence of female hormones in the mammary glands seems
to contribute to mammary tumours. Studies suggest that unspayed
bitches are at an increased risk of developing mammary tumours,
and it seems the earlier you spay the better. Many vets
recommend a bitch be spayed before her first season, which
will reduce the rick of developing mammary tumours to less
than 1%. Even if the bitch is spayed before her second season
her chances of developing mammary tumours is still greatly
reduced (approx 8% risk). If the bitch has her second season
and is still not spayed her chances of mammary tumours has
now increased to 25% i.e. there is now no reduction in the
risk.
While the benefit of spaying seems to decrease with each
oestrous cycle, some benefit has been demonstrated in bitches
even up to 9 years of age. Spaying also has many other advantages.
Spaying will of course stop unwanted pregnancies but is
also carried out for a number of other reasons such as phantom
pregnancies, infections like pyometra and, as we have mentioned,
a reduction in the risk of mammary tumours and cancers.
To some extent it is also thought that a dog who is overweight
in the first year of life has an increased risk of mammary
tumours later in life.
The key to longevity in the case of mammary tumours is early
detection. Perform regular monthly checks, especially on
middle aged bitches who are unspayed or who were spayed
later in life. If you notice anything unusual at all, take
your dog to the vet for a thorough check-up. Never wait,
even for the smallest nodule. Don’t wait a few weeks
to see if the lump will go away. Get it seen to straight
away.
Your vet will most likely want to know your dogs history,
date of spaying if applicable, what symptoms you first noticed
and when. They may do a physical exam and general blood
work, looking at the dog's general health and also looking
for evidence of any spread to lymph nodes and lungs. The
vet may or may not perform a biopsy to establish the type
and invasiveness of the tumour.
For small tumours up to about 2cm, surgery is often performed
to remove the tumour, whether it is benign or malignant.
The prognosis in these cases is good. Surgery can even be
curative if the tumour has not yet spread.
Even for tumours up to 5cm in size if there has been
no spread to the lymph nodes or lungs, surgery can prove
very successful.
During surgery for mammary tumours the vet may perform
a lumpectomy or may remove the entire mammary gland
(mastectomy). Removal of the tumour, mammary gland and
surrounding tissue minimises the risk of spread. The
entire line of mammary glands may be removed. |
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If your bitch is young and not yet spayed the vet will likely
suggest she is spayed as well, to lessen the chance of reoccurrence.
After surgery it is important to attend all the follow up
checks and to continue to check your dog yourself at home,
in case of reoccurrence.
If
the tumour is large, cancerous and has already spread then
surgery is no longer an option and there is currently no effective
treatment for secondary mammary cancer in dogs. Chemotherapy
is rarely used or successful. Surgery may be used to improve
the quality of life. Unfortunately mammary tumours in male
dogs are often aggressive and the prognosis is poor. The prognosis
for inflammatory carcinomas is also poor.
Mammary
tumours in dogs, especially older unspayed dogs, is unfortunately
quite common but there is so much you can do. Being proactive
will certainly increase your dog’s chances. Prevent
where possible, diagnose early and act swiftly.
Sources:
http://www.caninecancer.com
http://www.petmd.com
http://en.wikipedia.org
http://www.animalcancertrust.org.uk
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