Dog Tumors-What You Need To Know

dog cancer

Hearing the diagnosis from your vet that your dog has cancer may be one of the most difficult things you’ll ever hear.

Similar to humans, dogs also are prone to tumor growths also. In general, once a dog tumor has been tested and determined to be benign, there shouldn’t be a major cause of concern unless the tumor is causing significant additional health issues.

Unfortunately, the cancer rate of dogs is fairly high and is more prevalent amongst older dogs and is now one of the leading causes of death among dogs today. According to The National Cancer Institute’s Center for Cancer Research, approximately 6 million of the 65 million pet dogs in the United States will be diagnosed with cancer each year.

In an additional scientific study carried out in 2011 by the University of Georgia College of Veterinary Medicine, researchers found that cancer was the leading cause of death in older dogs. Even more disturbing is that cancer is the number one killer for 71 out of 82 breeds of dogs examined.

What Do Dog Tumors Look Like & How Are They Diagnosed

Some initial indications of cancerous tumors may include skin wounds that take a long time to heal or don’t heal at all as well as sudden weight loss and lethargy. As a general rule of thumb, extreme, sudden and unexplained causes of behavior in your dog should be red flags for which you should take your pet for a visit.

On the other hand, certain skin irritations or small growths may be benign however it’s recommended to take your pet to the vet for an exam to be sure.

What’s the Different Between a Growth & Tumor?

In general, your vet may term any type of growth or lump under your dog’s skin. Many vets however, prefer avoiding the term tumor unless it’s discovered to be malignant.

dog tumor 

How Will the Vet Diagnose My Dog’s Tumor?

There are a number of exams that need to be carried out when an unknown growth is discovered on your dog’s skin. Many times, advanced diagnostic exams are required in order to accurately determine whether or not the growth is indeed cancerous or not. Frequently, your vet will collect cells samples by inserting a very thin needle aspirate into the growth or via biopsy in order to validate whether or not the growth is cancerous. Furthermore, a biopsy can provide answers as to what type of cancer your dog has.

 For cases in which a malignant tumor is found, additional tests may be performed including:

  • Lab tests that may include exams such as blood tests, blood count and even in some cases a urine sample for analysis.
  • Radiographs (X-rays) – X-rays may show the appearance of additional abnormalities in addition to the tumerous growth (e.g. additional growths that may be developing)
  • Ultrasound, in order to determine the tumor’s proximity to organs and identify metastasis.
  • MRI / CT scan in order to better understand the composition of your dog’s tumor and see if it’s in the vicinity of any internal organs.

In general, many of these exams are typically carried out by a veterinary specialist. In order to perform a biopsy to determine the nature of your dog’s tumor, your vet will normally use anesthesia however in some cases a local anesthetic is sufficient, according to the location of the dog’s tumor. The biopsy itself uses either a needle or a surgical knife to cut out a very small part of your dog’s tumor from the skin and send it for evaluation at a lab.

What Are the Different Types of Dog Tumors?

The section below provides an overview regarding the more frequently occurring dog tumors. It’s important to keep in mind that dog cancer may not be the cause of the tumor and that signs of dog cancer extend beyond tumors only (however, some dog tumors may be malignant and require further treatment). 

Mast Cell Tumors

In general, mast cell tumors are one of the most common type of canine skin tumors. These types of dog tumors on the skin may grow quickly and are characterized by a red color and irritation on the skin due to the fact that they contain histamine, which is a chemical that causing itching and skin irritation.  Additionally, mast cell tumors can be characterized as minor bumps on the skin or can be tumors internally. In some cases, histamine causes an increase in stomach acid creation which may lead to gastro-intestinal ulcers and heart issues. An FNA test may also be carried out to determine the exact type of tumor. Excess histamine may lead to additional complications including vomiting and/or diarrhea and even loss of appetite in dogs.

Mast cell tumors frequently may occur in both the urinary and even in the digestive tract. These cases tend to be more serious with the tumors tending to be in more advanced stages of malignancy. On the other hand, mast cell tumors in the dog’s skin are generally more treatable.

Breeds With Heightened Risk

Short-faced dogs—including BoxersPugs, and French Bulldogs are all breed that have an increased risk regarding mast cell tumors although the good news is that the aforementioned breeds tend to develop small and less aggressive tumors which may be easier to treat if discovered early enough.

The Chinese Shar-Peis is a breed that has a higher risk of developing a more serious type of mast cell tumors.


Treatment essentially begins with proper identification which can be done via needle aspirate or or biopsy. A pathologist can determine what stage of growth the dog tumor is in.

The treatment for mast cell tumors often begins with a prescription of diphenhydramine in an effort to reduce the amount of histamine released in the body. Going forward, the vet and/or pathologist will classify the tumor into different grades, ranging from I, II, or II, with each grade essentially “rating” the level of malignancy of the tumor and its likelihood to metastasize.


Lipomas are essentially benign fatty tumors that consist of fatty tissue and generally not malignant and extremely common and may be characterized as soft bumps under the dog’s skin.  Lipomas may be movable and are generally not hard and in many cases they are not painful for the dog.

Lipomas may develop either on the dog’s skin but in some cases can develop internally and in cases of internal growth, the tumor may push up against the dog’s internal organs, causing pain. There does exist a malignant type of lipoma called liposarcoma and proper classification would be done after performing a biopsy or fine need aspirate.

Regarding type of breeds that are most likely to be affected, lipomas may affect a wide variety of dog breeds and isn’t limited to specific breeds in particular.

The size of the lipomas differs however in general, they do not pose a significant health risk.


For most cases of dog lipomas, unless the tumor is causing the dog pain, the tumor is many times left along and not removed.


This is a dog tumor type that is more likely to affect large and giant breeds like Greyhounds and Great Danes and many times occurs in the legs of these breeds. The first signs of this type of dog tumor is limping or a decrease in the dog’s mobility. While less frequent, this type of tumor may also affect the dog’s spinal bones also and can even develop to the lungs and lymph nodes.

In order to properly identify osteosarcoma, your vet will send you to perform an x-ray in order to make sure that the cause is osteosarcoma and not something another medical issue such as arthritis for example. Additionally, a biopsy may be necessary in order to reach a conclusion that your dog is in fact suffering from osteosarcoma rather than different conditions that may have similar symptoms.


Chemotherapy may be required to reduce the dog’s tumor and in many cases amputation is an unfortunate reality. In certain cases, it may be possible to remove the affected bone and insert a bone graft or metal rod in its place. This is most appropriate when the tumor is located in an area close to the distal radius (the lower bone of the front leg) and following the procedure your dog will need time to recover but this option for many is preferable than amputation of a leg or other afflicted limb.


Histiocytoma describes tumors in dogs that are caused by the immune system and frequently affect younger dogs (most likely less than 3 years old).

Affected breeds include English BulldogsScottish TerriersGreyhoundsBoxersBoston Terriers, and Chinese Shar-Peis.


In many cases, these types of dog tumors are not cancerous and will not spread within the body.

Histiocytomas are generally characterized as red bumps that develop rapidly on your dog’s skin. While these tumors are generally not cancerous, they can irritate your dog and cause pain and therefore in some cases your vet may suggest removing them (generally suggested for larger tumors that are painful). Sometimes histiocytomas are called “button” tumors as they vaguely resemble a button (small, red and above the skin). Histiocytomas may look similar to plasmacytomas however these plasma cell tumors usually affect older dogs and do require surgery.


Hemangiosarcoma is a type of dog cancer involving the blood vessels and is a dog tumor in the spleen. In the event of a rupture, the gums of your dog may become pale and they may display symptoms such as panting and shortness of breath and it may be hard for them to stand up and walk around. This type of dog tumor in the spleen may also be develop in the dog’s heart (generally found in the right atrium) and/or on the skin. Additionally, this is a type of dog tumor which is difficult to diagnose until the actual tumor ruptures.

Your vet will refer you to a pathologist to analyze a tissue sample and in many cases treatment requires surgery including removing the afflicted organ (e.g. spleen) in an attempt to stop the internal bleeding. Additionally, chemotherapy may be necessary to prevent the cancer from spreading in your dog’s body.

It’s most common in larger breeds like Golden Retrievers and German Shepherds and the prognosis tends to range anywhere from a few months to a few years, primarily depending on the severity and location of the tumor itself.


Melanoma is a type of dog cancer characterized by pigmented skin cells and this type of dog tumor tends to be a dark brown or black.   Malignant melanoma in dogs may happen around the area of the mouth and vets believe that it may be caused or accelerated due to sun exposure. This type of melanoma, oral melanoma, also tends to be a dark color.

In many instances, this type of dog cancer causes benign tumors but the actual growths may be very painful, especially on the nails.

Your vet will typically begin diagnosis with an x-ray and in many cases amputation of the affected toe may be required to avoid the cancer from spreading to other areas.

This type of dog cancer is associated with additional risks including the spread or metastasizing to different areas of the body, specifically the lymph nodes, lungs, liver and additional critical organs.

In cases in which the melanoma has spread, a therapy such as radiation or chemotherapy or even surgery may be recommended by your vet. Additionally, there does exist a therapeutic vaccine for this type of dog cancer that has been authorized by the USDA. Chemotherapy tends to be a less effective route of treatment for dogs.


This type of dog cancer is often accompanied by symptoms including lethargy, loss or significant reduction of appetite and weight loss as well as ongoing cough. Lymphoma is not a cancer which exhibits tumors but rather targets the lymphatic system and therefore one of the first signs of canine lymphoma is enlarged lymph nodes. The swollen lymph nodes however, may resemble a tumor but are actually only swollen and not a separate growth.  Additional areas include around the mouth and around the shoulders and knees. Furthermore, this type of dog cancer can target the nervous system and/or the gastrointestinal system.

The process to ascertain if it fact your dog has lymphoma cancer begins with a fine needle aspirate or tissue biopsy with the most common treatment today consisting of a chemotherapy treatment.

Chemotherapy is a type of dog cancer which can affect all breeds of dogs.


Papilloma are essentially benign tumors that are warts in dogs. These warts, while generally benign, are painful for your dog and can include symptoms such as swelling and painful infections.  Affected areas tend to be around the lips, mouth and eyes and can make eating difficult, thereby leading to weight loss issues.

In most cases, papillomas, which are caused by the papillomavirus, generally tend to disappear by themselves in most cases within a few weeks. The warts may be surgically removed by a vet in extreme cases such as if they’re causing extreme pain to your dog and if they’re not able to eat because of them. The warts themselves slightly resemble cauliflower. There is a long incubation period of the papillomavirus during which no symptoms are visible and therefore during that time it’s possible that the virus contamination may have spread to additional areas in the house or to other pets you may have.


dog with tumor

Additional Types of Growths in Dogs

Different growths of certain kinds may be more common among older and any strange or new growth you see on your dog should be a red flag to consult with your vet.

Most times, one of the main reasons for removing a growth that is benign is because it’s painful for your dog. The list below describes additional growths on their skin that your dog may experience.

Skin tags on dogs very much resemble skin tags that people also get, especially older men and women. In certain cases, they can grow to be fairly large but they tend to almost always be benign. No specific treatment for dogs’ skin tags is necessary unless they’re causing significant pain for the dog or causing additional health issues.

Squamous cell carcinoma – this is a type of dog tumor that is frequently onset due to excess exposure to the sun with commonly affected areas being around the mouth and on the skin. These tumors are characterized by a pink or red color and may seem to be raw and irregular skin. Additionally, this dog tumor may appear around the gum and in the tonsils of your dog.

Dog Cysts - Cysts are basically skin growth that are filled with fluid. They are growths that can be found in a variety of places in the dog’s body and can be on top of or under the dog’s skin. For small, insignificant cysts, your vet may simple decide to take a “wait and watch” route and not remove them immediately unless they are causing pain or other health issues however in many instances your vet with take a small sample to ensure that the growth is benign.

Sebaceous cysts are a kind of cyst that contains sebum. In many cases, these cysts may be initially thought to be tumors but are actual benign growths and sometimes may be diagnosed (improperly) as being a malignant tumor known as a sebaceous gland adenocarcinoma. 

Canine Oral Growths - There are several different types of growths that can affect your dog that tend to be found around the mouth area. Scratching and rubbing the mouth area may be signs of a growth or tumor in your dog’s mouth. One type of growth in the dog’s mouth that may occur is known an epulis. Essentially, an epulis is a growth on the dog’s gums and while in the majority of cases these are benign growths, it’s recommended to have them examined because in some cases they can be malignant.

Another condition some dog’s may suffer from is a dog tumor known as gingival hyperplasia which also is generally benign and is an overgrowth of the dog’s gum tissue that can resemble a tumor. In situations in which the extra tissue growth is painful for the dog during eating or other exercises, your vet may decide to remove the tissue. Either way, the tissue should be sent for a pathology exam.

In certain cases of dog’s tumors around the mouth and facial area, an x-ray may need to be performed. Treatment may involve removing the tumor while using an anesthetic before carrying out the x-rays. Should the underlying cause of the tumor be related to dental or gum disease, it may be necessary to perform a thorough dental cleaning as well.

Canine Mammary Tumors

Mammary tumors are growth in or around the mammary glands of female dogs of different breeds and this is a condition that should be examined immediately. The inflammation of these mammary glands is known as mastitis. Tumors may potentially be the cause of the inflammation of the mammary glands. These types of tumors may be benign or malignant with more malignant cases occurring in female dogs that haven’t been spayed (another reason to spay your dog). It’s estimated that approximately 50% of these types of tumors are malignant with a survival rate of 50% for the malignant tumors discovered.

Abdominal Masses

In some cases, there is a condition which tends to affect older dogs known as abdominal masses. In many instances, abdominal masses are identified after the abdomen area of the dog is palpated upon exam and/or after performing a routine abdominal radiograph at your vet. The type of treatment required is dependent upon the proximity and exact type of tumor.

It’s fairly common for the abdominal masses to be found to be malignant and located in close proximity to an organ. If an abdominal mass is suspected to be present, a series of exams will be necessary, most often beginning with a radiograph and/or ultrasound. A radiograph may be performed to determine if the growth has spread to the lungs or other areas in the chest cavity.

Many times your local vet would refer you to a specialist to perform the advanced exams required for situations such as these. In certain cases a biopsy may be adequate to determine if the dog’s tumor is malignant or not. If possible, treatment consists of surgery to remove the tumor. Abdominal masses may be difficult to identify and that’s another reason to schedule regular checkups with your vet.

Thyroid Carcinoma

Thyroid carcinoma is a dog tumor that is generally observed in older dogs. It’s characterized as a lump that tends to appear around the neck area and if you pet your dog, you may be able to feel a slight bump under the skin. In some cases this dog tumor can affect your dog’s thyroid hormone and lead a range of thyroid disorders. Thyroid disorder in dogs can cause a wide variety of symptoms including weight loss, nausea and additional symptoms. Treatment involves surgical remove and radiotherapy to ensure that the growth doesn’t spread.


Due to the high level of complexity in correctly diagnosing the many different types of dog tumors and due to the high risk potential involved, it’s prudent to take your dog on a regular basis to the vet as well as taking your dog immediately for examination if any irregular symptoms or behavior is observed.

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