benign tumors

Can dogs get breast cancer? Learn about Mammary Tumors in Dogs

October is Breast Cancer Awareness Month. Every October, we are reminded to spread the word about breast cancer prevention and early detection. That awareness extends to our dogs as well.


What is a mammary tumor (breast cancer)?

A mammary tumor develops as a result of abnormal replication of the cells that make up the breast tissue. Mammary tumors can be benign (non-cancerous) or malignant (cancerous). These two forms of the disease have different diagnostics, treatments, management, and prognosis.


There are several different types of malignant mammary tumors, with carcinomas being the most common. Carcinomas arise from epithelial (skin) cells, tubules of the mammary glands, or other cells found in the mammary chain. There are other cancers that can affect mammary glands, including osteosarcomas.


What causes this cancer?

The exact causes for the development of mammary tumors in dogs are not fully understood. It is well known that exposure to specific hormones, namely progesterone, increases the risk for developing mammary cancers in dogs. This is because progesterone stimulates growth factors (molecules that stimulate specific processes in the body) that cause mammary cells to multiply (i.e., replicate).


The incidence of these tumors is related to whether a dog is intact or has had an ovariohysterectomy (i.e., has been spayed). Dogs spayed prior to their first heat (also called estrus) have only a 0.5% risk of developing mammary tumor(s). However, after a first or second heat, this dramatically increases to a risk of 8% and 26%, respectively. Age also appears to play a role; the risk of tumor development significantly increases once a dog reaches 7 years of age and continues increasing until 11-13 years of age. This increased risk is breed dependent indicating that there is a genetic component.


Certain breeds appear to be more commonly affected, including Chihuahuas, Poodles, Dachshunds, Yorkshire Terriers, Cocker Spaniels, Brittany Spaniels, English Setters, Boxer Dogs, and Doberman Pinchers. Research in veterinary medicine continues, but to-date we still know little about which genes and mutations can lead to the development of mammary tumors in dogs. In human medicine, research has established a definite relationship between the BRCA gene (or breast cancer gene) and the development of breast cancer


What are the signs that my dog has this type of tumor?

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The most common clinical sign of a malignant mammary tumor is one (or more) palpable masses underneath the skin of the abdomen. They may be next to or within the nipple and follow along the mammary chain. The size of the mass(es) and their appearance may vary, but they are usually firm and nodular. Occasionally the skin over the mass may ulcerate (open) and bleed, and the affected area may feel warm to the touch and become painful. The mammary gland may even develop a discharge.


If the tumor has metastasized (spread to other areas of the body), other signs may become evident. Your dog may generally feel unwell, eat less, become lethargic, and lose weight. If the lungs are involved, your dog may have problems with breathing or develop a cough.


How is this type of tumor diagnosed?

These tumors are typically found as either singular or multiple nodules along your dog’s abdomen during a physical exam. Other procedures are then performed to determine the type of tumor and whether it is benign or malignant.


A common procedure to diagnose this tumor is a fine needle aspiration (FNA). FNA involves taking a small needle with a syringe and suctioning a sample of cells directly from the tumor and placing them on a microscope slide. A veterinary pathologist then examines the slide under a microscope.


In some cases, results from FNA may not be entirely clear and a biopsy or removal of the entire tumor may be necessary. Pieces of the tumor are then examined by a veterinary pathologist under the microscope. This is called histopathology. Histopathology is not only helpful to make a diagnosis but can indicate whether it is benign or malignant, and therefore how the tumor is likely to behave.


Given the risk of metastasis (spread to other areas of the body) with malignant mammary tumors, your veterinarian may also recommend staging (searching for potential spread to other locations in the body). This may include bloodwork, urinalysis, X-rays of the lungs, and possibly an abdominal ultrasound. The lymph nodes associated with the mammary glands may be sampled by FNA even if they seem normal.


How do malignant mammary tumors typically progress?

The way malignant mammary tumors typically progress is entirely dependent on the type and size of the tumor(s), and whether metastasis has occurred. Larger tumors (those greater than 3 cm) and those with evidence of spread have a poor prognosis. Tumors smaller than 1 cm have a better prognosis. Detecting and treating these tumors when they are small and before spread has occurred will provide your dog with the best chance for long-term control.


What are the treatments for this type of tumor?

For dogs with solitary mammary tumors, surgery is by far the best treatment. If there is only one small mass and staging shows no evidence of spread, surgery may be the only treatment your dog receives.


For dogs with multiple tumors of one or both mammary chains, the associated – or all – of the mammary glands may need to be removed. If your dog is intact, an ovariohysterectomy (spay) is recommended and may be done at the same time as the mammary gland removal.


For dogs with larger tumors or evidence of spread to other areas of the body, chemotherapy is typically recommended. There is increasing evidence that radiation therapy may provide some benefit for dogs with inflammatory carcinomas in addition to chemotherapy. Your veterinarian will discuss the options that are best suited for your dog’s particular situation.


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dog health

My dog has a growth. What do I do?

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Lipoma in Dogs

Lipomas are subcutaneous (underneath the skin) masses or tumors that develop commonly in dogs. They are usually soft, with limited mobility under the skin. The overlying skin is usually not affected. Over time they can grow larger and can impede movement if they are located between the legs or low on the chest. Most dogs that develop a lipoma will develop multiple tumors. But, it is important to recognize that additional masses do not necessarily indicate malignancy or metastasis. Since other cutaneous masses may appear similar to lipomas, it is recommended that every mass be checked individually.

Another subclassification of benign lipomas is infiltrative lipomas. These typically invade locally into muscle tissue and fascia and may need to be removed.

Liposarcomas, on the other hand, are malignant and can spread (metastasize) to the lungs, bone, and other organs. These tumors are rare but are indicative of the importance of examining all subcutaneous masses respectively.

Symptoms

Most lipomas feel soft and movable under the skin. They usually do not make pets uncomfortable unless they are in a location where normal movement is disrupted, like in the axillary region under the front leg (armpit). Often they are located on the belly or trunk but can be anywhere on the dog’s body. Most dogs with one lipoma will eventually develop several.

Diagnosis

Your veterinarian will do a complete physical exam, checking for all palpable masses. A fine needle aspirate will indicate whether the mass is a benign lipoma, or whether it is a more worrisome masses that is mimicking a lipoma. If the aspirate is inconclusive, surgical removal and histopathology may be necessary to arrive at a clear diagnosis.

Infiltrative lipomas may require computed tomography (CT) or magnetic resonance imaging (MRI) to adequately understand the mass and tissue location. This can be important information for the surgeon to decide how much of the mass can be removed and what approach needs to be employed for surgery.

Treatment

Most dogs will not need to have their lipomas removed. However, if the lipoma is restricting movement in any way it will be necessary for your dog's comfort to remove the lipoma. In addition, if any diagnostics indicate the mass may be a more aggressive tumor, it may be advised to have the mass removed while your dog is still under anesthesia. Removal tends to be a simple process if the mass is small because lipomas are benign, meaning that they have not invaded the body, and a large margin is not needed.

However, one type of lipoma, the infiltrative lipoma, can require a more complex procedure. As the name implies, infiltrative lipomas invade into muscle tissue and fascia and can make complete surgical excision difficult. Radiation therapy has been used for infiltrative lipomas and may be used alone, or in conjunction with surgical excision.

Living and Management

Other subcutaneous masses, such as mast cell tumors, can mimic the appearance of a lipoma. It is vital to make sure that every mass is evaluated individually in the event that one of the masses is malignant. You will need to continue to monitor your dog's lipomas, noting any changes in size, number, or location.


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Related: We have more information under our dog health category.

Can animals have high blood pressure?

Just like people, our pets have blood pressure too and they also risk developing high blood pressure. While high blood pressure in humans can cause more serious health issues, high blood pressure in animals is usually associated with a more critical health issue, because hypertension is typically the result of an existing underlying disease.


High blood pressure in dogs is often associated with Cushing’s disease or hyperadrenocorticism. Cushing’s disease is when a disorder, usually a benign tumor, allows an excess of cortisone to be released into the bloodstream.

Cats often develop high blood pressure as a result of having hyperthyroidism and/ or kidney disease. Hyperthyroidism is an overproduction of a thyroid hormone that results in increased metabolism.

If your pet has already been diagnosed with, and is being treated for, hypertension, your veterinarian will need to treat the underlying condition that caused the high blood pressure. It is also likely your veterinarian will also want to measure your pet’s blood pressure every three months moving forward. The vet may also suggest performing other tests, such as a complete blood count, blood chemistry panel, and a urinalysis every six months.

For most of us our pets are part of the family, so make sure they get a regular annual check-up with their veterinarian. Don’t ignore your vet’s advice, or at least get a second opinion before you make a potentially life and death decision on your fur baby's behalf.


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Don't forget to subscribe to our email newsletter for more recipes, articles, and clinic updates delivered to your inbox (here). Or, you can keep up to date by liking and following our Facebook page (here).

Related: We have more information under our dog health + cat health categories.