Benign and
malignant tumors of the
mammary glands
occur fairly frequently in unspayed female dogs, in fact they are the
most common type of tumor in the group. Spaying can largely reduce the
risk of developing this type of cancer, especially if the dog is spayed
before it has an opportunity to go into heat. There are two main types
of mammary gland breast tumors, each with several subtypes of tumor
growth.
The mammary glands' function is to produce milk to feed newborn
puppies. They are located in two rows that extend from the chest to the
lower abdominal area; the nipples indicate their location on the trunk
of the body. While this condition is more likely to occur in the female
population, it does also affect male dogs, albeit rarely. When a male
dog is affected by a tumor of the breast, the
prognosis is much more guarded and grave.
A genetic basis is possible in some breeds, and there are frequently
some genes that can be identified in dogs that are predisposed to cancer
of the mammary glands. For example, toy and miniature
poodles, English springer spaniels, Brittanys, cocker spaniels, English
setters, pointers, German shepherd dogs, Maltese, and Yorkshire terriers
have been reported to have an increased risk of developing breast or
mammary tumors compared to other breeds. Median age is about 10.5 years
(range, 1 to 15 years of age); it is less common in dogs younger than
five.
Symptoms and Types
- Usually slow-growing single or multiple masses in the mammary glands - about half of patients have multiple tumors
- May have superficial loss of tissue on the surface of the skin over the mammary tissue, frequently with inflammation
- Mass may be freely movable, which implies benign behavior
- May be fixed to skin or body wall, which implies malignant behavior or cancer
About half of affected dogs will be diagnosed with the benign form of
mammary tumors, which may be classified as complex adenomas, simple
adenomas, fibroadenomas, and duct papillomas. The approximate
other half of dogs to be diagnosed with mammary tumors will have a
malignant form of tumor, which may be osteosarcomas, fibrosarcomas,
solid carcinomas, and papillary cystic adenocarcinomas, amongst others.
Causes
Unknown, although likely hormonal or genetic.
Diagnosis
Several diseases could account for the symptoms, so your veterinarian
will want to rule them out before arriving at a conclusion. You will
need to give a thorough history of your dog's health and onset of
symptoms.
A complete blood profile will be conducted, including a chemical blood profile, a complete blood count, and a
urinalysis. Diagnostics will include X-rays of the chest and abdomen, which may detect
metastasis. It will be necessary to conduct a
biopsy of the mass to fully determine its nature, whether benign or malignant. In addition, the
lymph nodes will be examined, and a sample taken from them for laboratory analysis.
Treatment
Surgery is the primary mode of treatment. The tumor(s) will need to
be removed. Depending on the age of your dog, the type of tumor is
present, and the rate at which the tumors have metastasized, your doctor
may remove the tumor only, or all of the tumor along with the
surrounding tissue, lymph nodes and mammary glands.
Some types of tumor are more invasive, rotting deeper into the tissue
or bone, making then very difficult to remove. In these cases, partial
removal of the cancerous mass and surrounding tissue may be performed,
and chemotherapy may be an option, but use of chemotherapy for breast or
mammary tumors is not typically used. Surgical removal of the tumor may
be as effective in terms of disease-free interval as radical
bilateral mastectomy is for humans.
Spaying
intact
bitches at the time of surgical removal of the breast or affected
mammary tissue is often the preferred method, and this may enhance
survival as it decreases the possibility of recurrence. However, this
depends on the age of your dog as well. If your dog is older, this
method will not be as beneficial. Your veterinarian will consult a
veterinary oncologist (cancer specialist) for additional or updated
information regarding chemotherapy in dogs.
Prevention
Spaying before the first heat or
estrous cycle will greatly reduce your dog's risk for developing breast or mammary tumors compared to an intact
bitch; spaying before the first heat or
estrus
is also suggested to markedly decrease the likelihood of developing
mammary tumors. Early spaying is the best method for prevention of this
form of cancer. If spaying is delayed until before the second heat or
estrous cycle the risk of developing breast or mammary tumors compared
to intact bitches increases to 8 percent.
If spaying is delayed until after the second heat or estrous cycle,
there is a 26 percent risk of developing breast or mammary tumors
compared to an intact bitch, and if spaying takes place after the dog
has reached 2.5 years of age, there is no sparing effect on the risk of
developing breast or mammary tumors.
Living and Management
Your veterinarian or a consulting veterinary oncologist will
recommend a treatment plan that will include managing your dog's health
at home, with follow-up progress visits to the veterinarian or
oncologist. Physical examinations and chest X-rays will be required one,
three, six, nine and twelve months following the initial treatment to
check for recurrence or changes in the tissue.
The prognosis and course the disease will take varies with the type
of breast or mammary tumor your dog has (for example, whether the tumor
is benign or malignant), as well as the size of the tumor, and the
presence or absence of metastasis.
Surgery for tumors that have not spread may be curative. For example,
median survival after surgical removal of the breast or mammary tissue
(mastectomy) with tubular
adenocarcinoma
is 24.6 months. Median survival after surgical removal of the breast or
mammary tissue (mastectomy) with a solid carcinoma is 6.5 months.
Benign tumors have an excellent prognosis after mastectomy. Carcinomas
that are less than five centimeters in diameter also usually have a good
prognosis for
remission,
if the excision is complete. However, regional lymph-node involvement,
which can be confirmed by microscopic evaluation, makes the prognosis
worse and full recovery may not be possible.
You should never ignore a breast or mammary
nodule,
or adopt a wait and see attitude towards it. A breast or mammary lump
should never be left in place and observed, as it can quickly
metastasize
when it is the malignant form, spreading throughout the body and
becoming untreatable before its severity is recognized. Early detection
and thorough surgical intervention is best.
Always make a plan for evaluation and possible surgical removal of
any lump in the mammary gland(s), if you have a female dog that you are
leaving intact for possible breeding. On the other hand, if breeding is
not essential for your dog, early spaying before the first heat or
estrus will markedly decreases the likelihood of her developing breast
or mammary gland tumors.