Mammary Gland Cancer in Dogs
What are mammary gland tumors?
Mammary glands are female organs that produce milk for feeding the young. Dogs have 5 glands on each side which
are drained by lymph nodes in the armpit and the groin. The development of cancer in the mammary glands has been
shown to be dependent on hormones and mammary cancer is one of the most common cancers in the female dog.
Based on available data, approximately 50% masses in the mammary glands are malignant.
Source: www.peteducation.com/images/articles/mammary_glands.gif
It is important to know that mammary cancer does not refer to a single disease but there are many different subtypes,
each responding differently to treatment and each with a different prognosis. The subclassification of mammary cancer is
as follows:
Benign tumors Malignant tumors
Adenoma Non-infiltrating carcinoma
Simple adenoma Complex carcinoma
Complex adenoma Simple carcinoma
Basaloid adenoma Tubulopapillary carcinoma
Fibroadenoma Solid carcinoma
Low-cellularity fibroadenoma Anaplastic carcinoma
High-cellularity fibroadenoma Special types of carcinomas
Benign mixed tumor Spindle cell carcinoma
Duct papilloma Squamous cell carcinoma
Mucinous carcinoma
Lipid-rich carcinoma
How common are these tumors?
dogs prior to their first heat cycle significantly reduces the cancer risk later in life. Spaying after dogs prior to their first
heat cycle significantly reduces the cancer risk later in life. Spaying after the second heat cycle does not provide any
advantage.
the second heat cycle does not provide any advantage.
What are the symptoms?
Mammary tumors can develop either as a single mass or as multiple masses within the mammary gland. Dogs and cats
have multiple mammary glands, all of which can develop one or more benign or malignant tumors. Benign tumors are
typically well defined and firm upon examination whereas the clinical symptoms of malignant tumors include rapid growth,
ill-defined boundaries, ulceration and/or inflammation. Inflammatory carcinoma subclass of mammary tumors is typically
rapidly growing, affects multiple mammary glands and is characterized by firmness, warmth, edema, erythema, thickening
and signs of pain. Extensive swelling (lymphedema) of a limb adjacent to the affected glands can be also observed.
How is the diagnosis made?
The diagnostic procedures include physical examination, blood and serum chemistry profiles, X-rays, and abdominal
ultrasound. Collecting cells with fine-needle aspiration for cytology evaluation is not a sensitive method to distinguish
malignant from benign cells but can help rule out other lesions such as inflammatory lesions or mast cell tumors. The
most definitive way to get a diagnosis on the pet's suspected mass is to obtain a tissue biopsy.
Do these tumors cause pain?
It is imperative that pets with cancer are provided with pain medication to relieve discomfort caused by the disease as
well as by the treatments. To learn more, please visit the Cancer Pain Management section.
What food should be fed to pets with cancer?
Pets with cancer need to be fed diets specifically designed to support a cancer patient. To learn more, please visit the
Cancer Nutrition section.
What are the treatment options?
Surgery
The primary goal of surgery is to remove the tumor and it remains as the treatment of choice with a few exceptions.
There are a variety of different procedures that can be used to remove the breast tumors and the choice of procedure is
determined by various factors of your pet's condition such as the size of the tumor, the number of lesions, etc.
Lumpectomy (also called nodulectomy) is typically performed on small benign nodules. Mammectomy refers to the
procedure that removes the affected mammary gland(s). Mastectomy refers to the procedure that removes all of the
mammary glands at once. The mammary tumors can spread to the adjacent lymph nodes, however, it is not very
common in dogs. The lymph nodes should be removed only if they are enlarged and cytologically positive for cancer or
whenever gland 5 is removed due to the close association of the lymph node with this node.
Chemotherapy
While chemotherapy is the standard of care for humans, its benefit in canine mammary tumors has not been fully
evaluated. Small studies support the benefit of chemotherapy but additional studies with larger number of patients need
to be done for confirmation.
Radiation therapy
As is the case for chemotherapy, veterinary oncologists don't have enough information to confirm or rule out the benefit
of radiation therapy in the case of mammary tumors.
What are the treatment associated risks?
The risks associated with the surgical removal of the mammary tumors include rare complications such as anesthetic
death and infection.
Are there any clinical trials investigating new treatments?
There are no clinical trials specifically designed for breast tumors in dogs, however, there are clinical trials investigating
novel therapies for general malignancy in dogs. To learn more about clinical trials open to enrollment in the United
States, please visit the Clinical Trials for Any Type of Tumor section. To learn more about veterinary clinical trials, please
visit the Pet Clinical Trials section.
To help Pet Cancer Center conduct more breast cancer clinical trials across the United States in order to make novel
and more efficacious therapies available to pets, please
What is the prognosis?
There are several factors that will influence the pet's prognosis including the type of the tumor, its size, lymph node
involvement, presence of metastasis, etc. The following table summarizes the prognostic factors which should not be
taken as absolute bu rather relative:
Source: Withrow Stephen J, and David M. Vail. Small Animal Clinical Oncology. St Louis: Saunders Elsevier, 2007.
Additional Resources:
Sources:
Mammary glands are female organs that produce milk for feeding the young. Dogs have 5 glands on each side which
are drained by lymph nodes in the armpit and the groin. The development of cancer in the mammary glands has been
shown to be dependent on hormones and mammary cancer is one of the most common cancers in the female dog.
Based on available data, approximately 50% masses in the mammary glands are malignant.
Source: www.peteducation.com/images/articles/mammary_glands.gif
It is important to know that mammary cancer does not refer to a single disease but there are many different subtypes,
each responding differently to treatment and each with a different prognosis. The subclassification of mammary cancer is
as follows:
Benign tumors Malignant tumors
Adenoma Non-infiltrating carcinoma
Simple adenoma Complex carcinoma
Complex adenoma Simple carcinoma
Basaloid adenoma Tubulopapillary carcinoma
Fibroadenoma Solid carcinoma
Low-cellularity fibroadenoma Anaplastic carcinoma
High-cellularity fibroadenoma Special types of carcinomas
Benign mixed tumor Spindle cell carcinoma
Duct papilloma Squamous cell carcinoma
Mucinous carcinoma
Lipid-rich carcinoma
How common are these tumors?
dogs prior to their first heat cycle significantly reduces the cancer risk later in life. Spaying after dogs prior to their first
heat cycle significantly reduces the cancer risk later in life. Spaying after the second heat cycle does not provide any
advantage.
the second heat cycle does not provide any advantage.
What are the symptoms?
Mammary tumors can develop either as a single mass or as multiple masses within the mammary gland. Dogs and cats
have multiple mammary glands, all of which can develop one or more benign or malignant tumors. Benign tumors are
typically well defined and firm upon examination whereas the clinical symptoms of malignant tumors include rapid growth,
ill-defined boundaries, ulceration and/or inflammation. Inflammatory carcinoma subclass of mammary tumors is typically
rapidly growing, affects multiple mammary glands and is characterized by firmness, warmth, edema, erythema, thickening
and signs of pain. Extensive swelling (lymphedema) of a limb adjacent to the affected glands can be also observed.
How is the diagnosis made?
The diagnostic procedures include physical examination, blood and serum chemistry profiles, X-rays, and abdominal
ultrasound. Collecting cells with fine-needle aspiration for cytology evaluation is not a sensitive method to distinguish
malignant from benign cells but can help rule out other lesions such as inflammatory lesions or mast cell tumors. The
most definitive way to get a diagnosis on the pet's suspected mass is to obtain a tissue biopsy.
Do these tumors cause pain?
It is imperative that pets with cancer are provided with pain medication to relieve discomfort caused by the disease as
well as by the treatments. To learn more, please visit the Cancer Pain Management section.
What food should be fed to pets with cancer?
Pets with cancer need to be fed diets specifically designed to support a cancer patient. To learn more, please visit the
Cancer Nutrition section.
What are the treatment options?
Surgery
The primary goal of surgery is to remove the tumor and it remains as the treatment of choice with a few exceptions.
There are a variety of different procedures that can be used to remove the breast tumors and the choice of procedure is
determined by various factors of your pet's condition such as the size of the tumor, the number of lesions, etc.
Lumpectomy (also called nodulectomy) is typically performed on small benign nodules. Mammectomy refers to the
procedure that removes the affected mammary gland(s). Mastectomy refers to the procedure that removes all of the
mammary glands at once. The mammary tumors can spread to the adjacent lymph nodes, however, it is not very
common in dogs. The lymph nodes should be removed only if they are enlarged and cytologically positive for cancer or
whenever gland 5 is removed due to the close association of the lymph node with this node.
Chemotherapy
While chemotherapy is the standard of care for humans, its benefit in canine mammary tumors has not been fully
evaluated. Small studies support the benefit of chemotherapy but additional studies with larger number of patients need
to be done for confirmation.
Radiation therapy
As is the case for chemotherapy, veterinary oncologists don't have enough information to confirm or rule out the benefit
of radiation therapy in the case of mammary tumors.
What are the treatment associated risks?
The risks associated with the surgical removal of the mammary tumors include rare complications such as anesthetic
death and infection.
Are there any clinical trials investigating new treatments?
There are no clinical trials specifically designed for breast tumors in dogs, however, there are clinical trials investigating
novel therapies for general malignancy in dogs. To learn more about clinical trials open to enrollment in the United
States, please visit the Clinical Trials for Any Type of Tumor section. To learn more about veterinary clinical trials, please
visit the Pet Clinical Trials section.
To help Pet Cancer Center conduct more breast cancer clinical trials across the United States in order to make novel
and more efficacious therapies available to pets, please
What is the prognosis?
There are several factors that will influence the pet's prognosis including the type of the tumor, its size, lymph node
involvement, presence of metastasis, etc. The following table summarizes the prognostic factors which should not be
taken as absolute bu rather relative:
Source: Withrow Stephen J, and David M. Vail. Small Animal Clinical Oncology. St Louis: Saunders Elsevier, 2007.
Additional Resources:
- www.vetsurgerycentral.com/mammary.htm
- www.thepetcenter.com/sur/mam.html
- http://maxshouse.com/feline_mammary_tumors.htm
- www.peteducation.com/article.cfm?articleid=220
Sources:
- Withrow Stephen J, and David M. Vail. Small Animal Clinical Oncology. St Louis: Saunders Elsevier, 2007.
- Morrison Wallace B. Cancer in Dogs and Cats: Medical and Surgical Management. Baltimore: Williams&Wilkins,
1998
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Last updated 6/7/09
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