Nothing seems to strike more fear into the hearts of dog parents than the dreaded “C” word. Hearing that your dog has been diagnosed with cancer is a heart-wrenching experience, bringing with it an entire range of emotions – fear, disbelief, anger, denial, and grief – that can feel overwhelming.
Cancer in dogs is one of the leading causes of canine death, especially in older dogs. Studies have shown that approximately 50% of dogs over the age of 10 years will develop cancer at some point in their lifetime, and of those dogs, approximately one in four will eventually die from it1. How cancer affects an individual dog depends on the type of cancer present, the age of the dog, environmental factors, and that particular dog’s genetic makeup.
The increasing rate of cancer in dogs is thought to be due in part to the fact that our dogs are simply living longer. Advancements in veterinary care, nutrition, and disease prevention are extending the lives of dogs well beyond what has been possible in years past. But with this good news comes the bad news – as our dogs get older, they are also at a higher risk for developing cancer.
What Exactly Is Cancer, Anyway?
Simply put, cancer is a disease where the DNA (genetic code) of a normal cell becomes damaged, causing the cell to mutate. This damage can be caused by a virus, radiation, exposure to chemicals (such as pesticides or herbicides), or some types of hormones. The negative effects of these agents build up over the years, which could explain why so many cancers affect older dogs.
The damaged cell begins to go rogue and starts replicating itself, unchecked. The resulting cells then invade surrounding tissue, where they induce new blood vessels to grow around them to supply them with nutrients. This is what allows the cancer to spread (or metastasize) to other areas of the body.
Cancer is known as a “multifactorial” disease, which means there is no single known cause. Both environmental and hereditary factors can contribute to the development of cancer in dogs.
The Most Common Types Of Cancer In Dogs
Although many different types of cancer can develop in dogs, these are the most common (in no particular order).
Lymphoma

Also called lymphosarcoma, lymphoma is a cancer of the lymph nodes and lymph tissue, but can also involve the liver, spleen, bone marrow, and other organs. Lymphoma is one of the most common cancers in dogs, and is the most commonly treated cancer in veterinary medicine.
Lymphoma is an aggressive cancer, but if caught early, it has one of the most successful treatment rates. Lymphoma is usually treated with a combination of chemotherapy drugs and the steroid prednisone. This protocol results in remission in approximately 60-90% of cases, with a median survival time of 6-12 months. In approximately 20-25% of cases, some dogs can live 2 years or longer after treatment. Without treatment, however, prognosis is very poor.
Mast Cell Tumors
Mast cells are immune cells in a dog’s body that are responsible for allergic reactions. They can be found in all tissues of the body, but when they are cancerous, they usually form tumors on the skin. These quickly-growing tumors range from benign (non-cancerous) to extremely aggressive and malignant (cancerous). When malignant, they have a tendency to spread to other areas of the body, so they should always be addressed immediately when they are found.
Treatment for a mast cell tumor usually includes surgical removal of the tumor. If the growth is benign and all of it has been completely removed, no further treatment is recommended. However, if the tumor is cancerous, treatment options involve radiation, chemotherapy, and steroids to suppress the immune system. Treatment and prognosis depends on how advanced and aggressive the tumor is.
Osteosarcoma
Osteosarcoma is cancer of the bone. Although it can occur anywhere in the body, it’s more commonly found in the leg bones of large and giant breed dogs (although dogs of any size can develop osteosarcoma). The most common symptom is pain and swelling in the affected leg, along with lameness that gets progressively worse.
Treatment for osteosarcoma in the leg is usually amputation of the affected limb, followed by chemotherapy. However, osteosarcoma is one of the more aggressive cancers in dogs, and it has a tendency to spread to other areas of the body such as the lungs and liver. Usually by the time swelling and lameness become apparent, the cancer has already begun to spread, making the prognosis for dogs with osteosarcoma very poor.
Hemangiosarcoma
Hemangiosarcoma is a highly malignant cancer that develops in the endothelial cells, which line the body’s blood vessels. It mainly affects the spleen, liver, heart, and skin, but can spread anywhere in the body. Hemangiosarcoma is common in Golden Retrievers, Labrador Retrievers, and German Shepherds.
This cancer develops very slowly and is essentially painless until it begins creating problems, so it’s often not caught until the disease is well-advanced. Many dogs actually die from severe internal bleeding before the cancer is even diagnosed. Treatment involves removal of the affected area, followed by chemotherapy and radiation. However, prognosis for most forms of hemangiosarcoma (with the exception of the skin form) is very poor – less than 50% of treated dogs survive longer than 6 months.
Mammary Cancer
Just like humans, dogs can develop breast, or mammary, cancer. Mammary tumors most commonly affect older, unspayed female dogs, or female dogs who were not spayed until after their second heat cycle.
Approximately 50% of mammary tumors are cancerous, while the other 50% are benign. Treatment involves surgically removing the tumor. Sometimes follow-up chemotherapy may be recommended. The good news is, if mammary cancer in dogs is diagnosed early, and the cancer has not yet metastasized, surgically removing the tumor oftentimes will completely remove all the cancer, giving the dog an excellent prognosis.
Oral Cancer

Oral cancer involves tumors of the mouth and throat. This type of cancer ranges from mild to extremely aggressive, so any oral tumors found in a dog’s mouth should be biopsied to find out the type and extent of the disease. Many oral tumors are found during routine veterinary teeth cleaning, another good reason to have regular dental exams performed on your dog.
Oral cancers are usually treated by surgically removing the tumor, with some requiring follow-up radiation depending on the type of cancer present.
Squamous Cell Carcinoma
This is one of the most common cancers found in dogs. Squamous cell carcinoma is a malignant cancer, mainly found in 3 areas of the body: the skin cells of the epidermis, in the mouth (on the gums or tonsils), and around the nail beds of the toes.
Complete surgical removal of the affected area is the treatment of choice for this cancer. Fortunately, fewer than 20% of cases metastasize, but it depends on the type and location of the tumor.
Melanoma
Melanoma arises from pigment-producing cells in the body called melanocytes. There are several types of melanoma found in dogs. With a few exceptions, almost all are malignant, and are found in the mouth, skin, and eyes.
Most malignant melanomas grow rapidly and spread quickly to other parts of the body like the lymph nodes, lungs, heart, spleen, and brain. Chemotherapy is ineffective against malignant melanoma. Radiation therapy can be used to help extend the life of a dog diagnosed this form of cancer, but once it has metastasized, little can be done.
Symptoms Of Cancer In Dogs

It’s important to be familiar with the warning signs of cancer. These include:
- Lumps, bumps, or any abnormal growth or swelling that doesn’t go away
- Rapid weight loss
- Unusual foul odor, especially from the mouth, nose, skin, or rectal area
- An open sore that won’t heal
- Any dramatic change in appetite
- Difficulty swallowing or eating
- Sudden onset of lameness, not related to an exercise injury
- Pale gum color
- Weakness and fatigue
- Swollen lymph nodes (especially in the neck, and around the hock area of the rear legs)
- Coughing, wheezing, or shortness of breath
- Chronic bleeding or discharge from the mouth, nose, ears, or rectal area
- Abdominal bloating or distension
- Black, tarry stools
- Chronic vomiting or diarrhea
- Fever
- Difficulty urinating or defecating
- Pain anywhere in the body
- Collapse
Also watch for any behavioral changes that are out of the ordinary. Is the dog sleeping in rooms he typically doesn’t go into, or hiding in unusual places? Also, a calm dog who suddenly acts snappy or aggressive may be in pain.
How Is Cancer In Dogs Diagnosed?
If you or your veterinarian find an obvious tumor or mass, the first step is to take a cell sample from the tumor. This is done by either sticking a needle into the tumor and drawing up some cells, or with a surgical biopsy. The cells are then sent to a lab, where a pathologist can examine and identify them.
Radiographs (x-rays) or ultrasound can also be used to evaluate whether there are any suspicious-looking growths in the lungs, liver, spleen, or abdomen. Your veterinarian can also run blood tests, which will show any abnormalities that could indicate cancer somewhere in the body. The vet may also take a urine sample for urinalysis.
Treatment Options For Cancer In Dogs
The goals of treating cancer are two-fold: to remove all cancerous tissue whenever possible, and to prevent any cancer cells that are there from spreading.
For many cancers (especially if they are caught early), there are several different types of treatment options available to either wipe out the cancer completely, or keep it at bay for a long enough period of time to extend the dog’s length and quality of life for as long as possible. Which method is used will depend on the type of cancer cells that are identified.
- Surgical excision – surgical removal of the tumor and any surrounding tissue that may have been invaded.
- Chemotherapy – the use of chemotherapeutic drugs (given either orally or through an IV) designed to poison and destroy all rapidly-dividing cells in the body.
- Radiation therapy – the use of highly-targeted radiation to kill malignant cancer cells. Radiation therapy is particularly helpful for targeting cells deep in the brain and nasal cavity, areas that were previously inaccessible to surgeons.
- Immunotherapy – the use of specialized drugs to stimulate the body’s immune system to recognize cancer not as the body’s own tissue, but as an invading disease that needs to be destroyed.
- Cryotherapy – using extreme cold to freeze and remove tumor tissue.
Unfortunately, with chemotherapy and radiation, normal cells in the body can also be damaged during treatment. This can lead to possible side effects such as nausea, vomiting, diarrhea, lethargy, weakness, and loss of appetite. These effects are usually temporary.
What’s The Prognosis For A Dog With Cancer?
The prognosis for a dog with cancer can be extremely difficult to state with any degree of certainty. There are many factors that must be taken into consideration: the type of cancer, location of the tumor, age of the dog, whether the cancer was caught early or in later stages, or if the cancer has already spread.

The good news is that modern cancer management doesn’t just involve killing cancer cells. Successful management of cancer in dogs includes pain control, good nutritional support, physical therapy, protection against stomach ulcers, and can also include the use of alternative therapies such as acupuncture, massage, herbal therapy, and diet therapy.
So what’s the overall success rate for dogs who undergo treatment for cancer? According to Dr. Dave Ruslander, veterinary oncologist and past president of the Veterinary Cancer Society, “Overall, for the malignancies that we see, it’s probably in the 60-plus percent range.” The patients who have discernible lumps and bumps removed seem to have the best prognosis, as do dogs who are treated in the early stages of lymphoma.
However, sometimes even dogs who are treated cannot achieve remission. For these dogs, many pet parents opt out of further treatment, and instead take their dogs home for palliative care (providing the dog with relief from pain and physical stress) until the dog’s quality of life declines to the point where euthanasia is the most humane option.
So What Should You Do If Your Dog Is Diagnosed With Cancer?
As a former veterinary technician, I was often asked by clients what I would do if it were my dog who was diagnosed with cancer. Having dealt with cancer in my own pets, I always answered truthfully: Ask yourself what is best for YOUR DOG. Not you, your veterinarian, your family, or your friends. Your dog. Every dog, like every cancer, is different. You must make the best decision you can based on the knowledge that you have, not only of the cancer itself and the treatment options, but of every unique and individual factor that makes up your dog.
The veterinary definition of successful remission usually means about 6 months. Your dog’s remission could be 3 months, or it could be 3 years. It’s important to remember that, unless the cancer was completely cured by surgical excision, in most cases cancer will eventually win the battle – it’s just a question of when. That doesn’t mean treatment is hopeless – far from it! But whatever you decide, don’t let guilt factor into your decision. Be the advocate for your dog. Your dog may not be a good candidate for treatment due to advanced age, other health issues, aggression, anxiety, or fear. Or perhaps, your love for your dog notwithstanding, due to circumstances beyond your control your family is simply not able to afford thousands of dollars for treatment. Every person’s situation is different.
Whatever you decide, examine your heart and do what you know is right for your dog. And only you know what that looks like.
Can Cancer Be Prevented?
The good news is, improvements in nutrition, medical care, disease prevention, and diagnostic procedures have helped today’s dogs actually live to ages when accumulated DNA damage can cause problems such as cancer. The bad news? It goes without saying.
So what can we do about it?
While not all cancer can be prevented, there are things you can do to help decrease your dog’s risk of developing cancer. Consider spaying or neutering your dog between 6 and 12 months to help prevent reproductive cancer. If you’re a smoker, either quit smoking or take steps to reduce your dog’s exposure to second-hand smoke. Make sure your dog stays at a healthy weight, has regular veterinary exams, and gets frequent exercise and good nutrition.
But the best thing you can do is to be diligent about monitoring your dog’s health. By far one of the most common ways pet parents detect cancer is by finding a lump or mass on their dog. Early detection of cancer, before it has a chance to spread, is critical for successful treatment.
If you do find something unusual on your dog, or if he is showing any of the warning signs of cancer, have him checked out immediately by your veterinarian. The “wait and see” approach is not a good policy to use when it comes to possible cancer in dogs.
And if your dog is diagnosed with cancer, always get a second opinion, preferably from a veterinary oncologist, to discuss all your options so that you can make the best decision possible for your dog.
Have you ever had a dog who was diagnosed with cancer? If so, what did you do? Please share your story with us in the comments below!
My parents dog has been in the family for almost 12 years. He has been getting slower and less energetic and we just found out that he has cancer. Thanks for explaining some of the basics of cancer in dogs and the treatment options. I think there are a few things that we can do to help him, but it seems like he is too old and weak to undergo a full range of treatment. Thanks for the info.
Hi Nathan, I am so very sorry to hear about your family’s dog. Cancer can be such a devastating diagnosis, especially in an older pet who may be weaker or suffering from other medical issues. If he’s not a good candidate for aggressive treatment, an oncologist may still be very helpful in helping you develop a treatment plan to keep him comfortable and extend his life for as long as humanely possible. Fortunately there are options available now for cancer treatment that we didn’t have access to even 5 years ago.
My heart goes out to you and your family. I had to say goodbye to my almost 15-yr old kitty with cancer last year, and I know how heartbreaking it can be. Just enjoy every day that you have with him and make as many good memories as you can while he’s with you. And know that you gave him a lifetime full of love… that’s the comfort we get to hold onto. <3
My 6 year old boxer has a large tumor on the top of her paw. I’ve taken her to three vets to get that second and third opinion. Of those three vets, only one is willing to take it off surgically, but he did say he wouldn’t be able to have any clean margins. Since this apt (2 months ago), I found two more lumps on her… I know we can have them all surgically removed but I wonder if it’s what’s best for my girl. I love her to pieces and it’s a heart-wrenching decision… with three tumors, one of which definitely doesn’t have clear margins, should I get them removed? One question I have is, if I get the tumor on her paw removed, is there any way that some rogue cancer cells will spread at the time of removal thereby worsening her condition? Or should I leave the tumor on her paw and pray that it’s a slow-growth tumor? I’ve been going back and forth with my decision so much I don’t know which one is the best… it feels like gamble either way. Any advice or tip would be so appreciated.
Hi Melissa, I’m so very sorry to hear about what’s going on with your girl. 🙁 Boxers can be prone to developing various kinds of lumps and bumps (some cancerous, some benign). One question…have all these lumps been biopsied and definitely been diagnosed as cancerous? If so, were any of the 3 vets you’ve seen a veterinary oncologist? If the lump on your dog’s paw is cancerous, I would definitely consult with a veterinary oncologist first regarding both the option for surgery and any follow-up treatment. An oncologist will be able to give you the most information regarding what type of cancer you’re dealing with and how it behaves in the body, as well as a clear expectation for prognosis. Since Boxers can develop several different types of lumps, it’s also possible that the lump on her paw could be one type of tumor and the other lumps could be something completely different.
Regarding cancer cells spreading after surgery, you are correct in that it can be a risk factor. Mast cell tumors in particular are notorious for causing issues throughout the body if they are disturbed (such as during surgery). Also, tumors on the feet can be difficult to remove completely due to the anatomy of the foot and all the structures (bone, ligaments, and tendons) that the tumor could be growing around. In order to make the most well-informed decision, in my opinion you’d first need to know exactly what type of tumors these are, and then consult with an oncologist. Since your girl is only 6 years old, if her condition is treatable, she could have many more years with you! And if the other lumps are benign (many older dogs develop lipomas, which are benign fatty tumors that don’t necessarily need to be removed unless they are located in an area where they are causing the dog discomfort), you’d only need to worry about the tumor on her foot. Either way, a good veterinary oncologist is a great place to start. He or she will be able to work directly with you to discuss all available options, then create a treatment plan that is customized for you and your dog.
Please let me know what happens and what you decide…I’m wishing you the best of luck, and hoping for a positive outcome!!
Hi dear, really a great information about 10 warning sign of pet cancer. Not too many people would truly think about this the way you just did. I hope it will create some awareness among the pet owners and hope they will be careful while facing these types of problem. I’m sure it will be very beneficial for all pet lovers. A few months ago I have attended a conference about Investment Opportunity in the Development of a New Cancer Drug, which was arranged by PetLife Pharmaceuticals at Maryland, and they were researched and preparing a medicine for avoids the Pet cancer and makes your pets live long. I have also invested few Dollars in that company, for which it will help them for more research. Thanks for sharing.
My 18 yr old dacshund has just been diagnosed with tonsillar cancer.
He is on pain relief , we have decide on palliative care dur to his great age.
My question is , if we have him put to sleep at home when the time is right , should we let his brothers be present ? They are very close, sleep together, and support each other etc . I feel,they should be part of the process but and not absolutley sure , so would appreciate some feedback .
Hi, Mo. I’m so very sorry to hear about your dog’s cancer diagnosis. 🙁 First, I think it’s an excellent idea to let him remain at home when it’s time to let him go. I have arranged for that service several times for my pets, and I wouldn’t do it any other way now. Letting him be at home, surrounded by familiar sights and smells, will not only be much less stressful on him, it will also give you the peace of mind that he will be as comfortable as possible.
Regarding your question about letting his brothers be present, I might be able to offer some insight around that situation that could possibly help you decide. I faced that question with my own pets too, and I ultimately elected not to have them present during the actual injection by the veterinarian, but I did let them see their brother afterwards. I made that decision because I knew from seeing similar situations in the veterinary hospital where I worked that animals are not only extremely smart, they are also very sensitive and capable of experiencing great distress. If they witness a stranger in your home (whether or not that person is dressed like a veterinarian) giving an injection that leads to their brother passing away, they only see the outcome and aren’t able to understand that this action was actually a humane and caring act. In my mind, it could possibly lead to them being afraid of people whom they don’t know ever visiting your house in the future; or if the veterinarian is dressed like (or smells like) a vet during the procedure, they could make that association as well and become afraid of the vet.
In my situation, I ultimately decided that it was better for them to be in a separate room during the procedure, and then allow them to come out to visit after the vet had already gone. This way they do have some closure (although don’t be surprised if they still search for their brother around the house afterwards – that’s happened to me too).
I hope this is helpful in making a decision. Please accept my sincerest sympathy… even when our babies are older and have lived a long life, it still doesn’t make it any easier to say goodbye. My heart goes out to you and your family. <3
Thank you Camille, that is a huge help, and I think an excellent idea that we will probably do.
The vet said she would wait until the other two were ready to leave him before she took him away, but after reading your remarks, I reckon she could go and I will take him to the vet later as he is going to be cremated , that way they can spend some time with him if they need to .
He has has a great life, and is a wonderful character, very talkative , so the house will be very quiet when he is gone. I am just not looking forward to the deterioration in his condition.at the moment he is as normal , but the oncologist gives him 4 months at best, so it is going to be pretty quick .
Again thank you so much for replying, you advice has helped my decision enormously,
Mo x
You’re very welcome Mo, glad I could be of help. I think that’s an excellent idea to take him to the vet later and give his brothers as much time as they need. They may choose to be around him for awhile, or they may be a little skittish – either way is perfectly normal since every dog reacts differently.
He sounds like such a wonderful dog. Enjoy each day with him, and just know that, no matter what, you gave him a long, happy life filled with love. My thoughts are with you. <3