Most Common Cancers in Dogs

Thanks to the increased awareness about responsible pet ownership, advances in veterinary medicine, and improvement in the quality of canine nutrition and preventative health products, modern-day dogs live much longer than the generations that came before them. 

While that means we get to spend a few more years with our beloved pooch, it also means that we will see them go through the degenerative effects of ageing. It’s not easy to watch them move around with creaky joints, or suffer from episodes of mental fog, but that is to be expected as any animal moves through the aging process. But one condition that we would hate to see in any dog, and yet happens quite often in geriatric ones, is cancer. 

Cancer is a disease characterized by the uncontrolled proliferation of abnormal cells. Just like human cancer, canine cancer can happen in different parts of the body. This is one of the reasons why catching cancer early is difficult--oftentimes, you don’t know what you’re looking for. In addition, the progression can be insidious and the symptoms subtle. The symptoms of canine cancer vary greatly depending on where the neoplastic growth is found, but common symptoms include chronic weight loss and chronic vomiting or diarrhea. 

Unfortunately, the incidence of canine cancer is not exactly low. A Veterinary Medical Database study spanning 20 years with a sample of 74,000 dogs found that cancer was the most common cause of death in 89% of the dog breeds included in the study. With those numbers, the chances of canine death due to cancer is three times more likely than death due to traumatic injuries. 

If you own a senior dog, familiarizing yourself with the conditions that afflict them is helpful in staying vigilant. With that in mind, here are 5 of the most frequently diagnosed canine cancers according to the American Animal Hospital Association (AAHA). 


Mast cell tumor 

The mast cell is a special kind of white blood cell that sounds the alarm when something irritating and possibly dangerous gets in or on the body. It releases the globs of histamine into the bloodstream, causing symptoms that we recognize as allergies. In dogs, this manifests as severe itchiness and, less commonly, respiratory issues. When mast cells start increasing in number, paying no attention to regulatory mechanisms, you get a mast cell tumor. It can happen in any part of the body, but because a lot of mast cells patrol the skin, that’s where you’ll usually find them. These tumors may be raised or flat, swollen or ulcerated. They can change in shape and size quickly or look the same for months on end. When this mass of mast cells release histamine, the area reacts and becomes severely itchy and swollen, at times triggering a full-body response. 


Oral malignant melanoma 

This is among the most invasive and malignant cancers in dogs. This growth is found in the gums or the oral mucosa, causing pain and discomfort when eating. Affected dogs may drool or cause a mess when they eat or drink, all because they are trying not to aggravate the tumor in their mouth. Contrary to its name, the melanoma may not be pigmented with melanin. To differentiate it from other cancers of the mouth, your veterinarian will need to conduct fine needle aspiration and observe the sample under the microscope or in histopathological slides. 


Anal sac carcinoma 

The anal sac is the organ responsible for spewing out pungent, oily substances. While we humans may not be too fond of it, it plays an important role in canine social interactions. Unfortunately, this is one area prone to neoplastic growth. The risk of spreading to other organs is high, and its ability to invade nearby tissues is problematic. A big blob of growing tissue in the hind region will eventually interfere with your dog’s ability to defecate. Straining, ribbon-like feces, and the presence of swelling or protrusion in the anal sac area are tell-tale signs, but it must still be differentiated from anal sac impaction and hernias that present in similar ways. 



Lymph tissues are found in many organs in the body, as well as in discrete masses we know as lymph nodes. Their main role is related to the immune system, producing white blood cells that protect our dog from disease. However, these active tissues may also produce aberrant white blood cells. Metastasis is common because of the lymphatic vessel system that connects one lymph organ to the other. The symptoms of lymphoma include general weakness, decreased appetite, vomiting and diarrhea. A wide variety of other conditions can present the same way, which makes laboratory work and other diagnostic tests very important. 


Mammary gland cancer 

Breast cancer is prevalent among women, so it’s no surprise that mammary tumors are prevalent among female dogs as well. There are many kinds of tumors that can occur in this area, owing to the different kinds of cells present. What they all have in common is the presence of estrogen receptors. This is why spaying dogs is a great way to decrease  your furry buddy’s chances of getting mammary gland cancer--without the ovaries secreting female sex hormones, tumor cells do not receive the trigger they need to grow. 



Canine cancer is a frightening prospect to any fur parent, but we are not powerless against it. If you own a senior dog, the most important thing you can do is  enforce preventative health measures. This involves giving a complete, balanced diet appropriate to your dog’s age, supplementation for bone and joint health, a healthy amount of exercise and mental stimulation, and visit to the veterinarian at least every 6 months for routinary diagnostic testing and health checks. 

With love, care, and extra attention, every senior dog can continue to live out their life in health and happiness.


For educational purposes. No product claims implied.