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Mammary Gland Tumor in Dogs

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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.




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.



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