signs of cancer in dogs

10 Signs of Cancer in Dogs to Look Out For

Proper care and nutrition help boost the immune system of dogs, guarding them against common diseases and prolonging their life. However, canine diseases are normally the result of a wide range of factors, including genetics, exposure to harmful stimuli, physical trauma, nutrition, and even age. Proper care alone cannot save your pet from the Big C.

Dr. Dave Ruslander, former president of the Veterinary Cancer Society, explains that as dogs get older, they become more vulnerable to infections and health problems. He added that about 50% of dogs aged 10 and above develop cancer, which is now the leading cause of death among canines. Doctors, however, recommend regular check-ups and meticulous observance, regardless of your dog’s age. Even the younger ones are not spared from cancer.

sick dog cancer symptoms

Early detection of cancer signs is key to saving the life of your dog. However, unlike humans, dogs are incapable of speech. This makes the task of knowing their health status difficult, leaving the owners dependent on behavioral cues and physical manifestations of the disease. Below are 10 of the telltale signs of cancer that dog owners must not ignore.

Suspicious Lumps

Lumps or masses in dogs are normal as they age and accumulate fat deposits over time. There are two categories of lumps in dogs: benign and malignant. The latter is more likely to lead to cancer, although this is not to say that benign lumps are safe and should be overlooked. Some benign lumps eventually turn malignant; they get bigger and complicate the neighboring tissues. Thus, it is important to perform a regular lump check on your dog once or twice a month, particularly if your dog is advanced in years already.

Lumps commonly develop under the skin and in mammary glands. You may focus on these areas as they are deemed cancer-prone. While the procedure can easily be done at home, you are strongly advised to consult a veterinarian once you feel a suspicious and concerning growth, especially when accompanied by other signs and symptoms. After all, the malignancy of a tumor or lump requires an analysis of the sample and there are sensitive areas like genitals and breasts that are best left to the hands of an expert.

Mouth Sores

Mouth sores are difficult to observe since they are not visible on the outside. Most likely, they go unnoticed by dog owners unless they examine their pets’ body parts painstakingly or bring their pet to the veterinary clinic where a comprehensive check is performed. Mouth sores, particularly when accompanied by foul discharge or bleeding, can be signs of oral cancer. Given the difficulty in spotting mouth sores in dogs, it is advisable for caretakers to regularly brush their pet’s teeth and check the insides of their mouths in the process.

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Other than the sores and blood, the color and condition of your pet’s gums can also be indicative of a serious disease. Pale gums show that the dog has experienced blood loss and the reason can be cancer. If these visible signs remain unnoticed, the intense unpleasant smell of your dog’s mouth can be your red flag. Sores worsen the bacteria that naturally breed in mouths, thus the bad smell even after regular brushing.


A sudden lack of energy among dogs is a dead giveaway of an illness or injury. As a dog owner, you are most likely familiar with your pet’s usual energy level and demeanor on any given day. A shift in its mood often reflects something unusual in its health. It may be cancer or another disease. If your dog is already advanced in years and lethargic, its sudden loss of interest in a favorite activity, food, or object can be a sign of a health problem. Other concerning behaviors include breaks in routine, delayed responses, loss of appetite, and too much or lack of sleep.

In an interview, Dr. Ruslander explained that because canine cancer sometimes does not manifest visible signs until the latent stage, it becomes critical for dog owners to observe and not be complacent. Weariness, albeit a non-alarming sign, should be treated seriously.

signs of cancer in dog

Collapse and Syncope

Weakness or lethargy among dogs may not be that alarming to pet owners. But when dogs collapse without an immediate cause of physical trauma or injury, they should be rushed to the veterinarian for a comprehensive checkup. When your dog collapses, it may be too weak to muster up the energy to stand although it is still conscious. A collapse in animals can signify a range of possible problems, including circumstantial causes like dehydration, poison, and heat stroke. At the same time, they can also be due to serious cases of neurological, musculoskeletal, cardiac, and endocrine diseases. In some cases, these diseases develop into cancer.

Meanwhile, fainting or syncope is caused by the lack of blood flow to the brain. Here, the animal is completely unconscious for a period of time. Unlike humans, animals rarely faint unless an abnormality in their system occurs. Fainting in animals, suffice it to say, is uncommon. There are only two possible causes for fainting in animals, either they have neurological problems (e.g., brain seizures) or cardiac problems (e.g., unusual heart beat). So, when your dog faints, it should be enough reason to sprint all the way to the vet.

Unusual Movements

Does your dog limp, lean heavily on one side, or roll endlessly on the mat? These strange movements can be warning signs of pain that your dog experiences and endures. Since they are not equipped with the knowledge of proper pain treatment, they exercise behavioral mechanisms like non-use of an affected area (e.g., limping) or application of pressure (e.g., pressing a body part on a surface) to alleviate or avoid the pain. More so, they are not verbally equipped their pain to their human caretakers, so they resort to yelping for help at the very least. While it’s possible for these unusual movements to be caused by less serious diseases like arthritis or a slight bruise, pain can also be indicative of bone cancer. Do not take the risk and bring your dog to the doctor as soon as possible.

Abnormal Discharge

Foul discharge or bleeding is an outright cause for concern. It can be due to infection or a more serious disease like nasal cancer. In animals, abnormal discharges associated with cancer commonly occur in the facial areas like the eyes, nose, and mouth. The unpleasant smell of the discharge can indicate the severity of the disease. This should be enough for dog owners to immediately bring their pets to the nearest clinic.

Doctors explain that foul odor, even in the absence of any discharge or blood, must also be taken seriously by pet owners. Extremely bad breaths of your dogs can be caused by cancerous mouth sores, which escape the eyes of a regular observer. Bad body odor, meanwhile, can stem from the cancerous lumps hidden beneath the skin and fur.


Wounds per se are treatable and dangerous only when left unheeded. The body system of animals also has the natural ability to heal minor cuts and scrapes. For instance, animal platelets help prevent the continuous heavy flow of blood from wounds by forming a clot. Nonetheless, according to the veterinary oncologist, Dr. Ruslander, wounds that persist over time are a classic sign of cancer. When foul discharges start to flow from the affected area, then dog owners should not wait for a day more before they have their dogs checked.


Seizures are sudden and uncontrolled bodily spasms or surges of movement such as leg jerking, twitching, and chewing. The pupils dilate and the muscles twitch. Seizures are possible signs of a wide range of diseases including liver disease, toxins, or brain tumor. All are serious diseases that require an outright action on the part of the owner, more so that the pets can appear normal even minutes before the episode. Knowing what to do during a seizure contributes to the survival of your canine pet.

When dogs experience seizures, they must not be moved unless their position can potentially cause them harm. Spasms do not cause the dogs any pain, after all. Owners must keep themselves calm. If it becomes necessary to move the dog, then grab them by the legs. Touching and comforting them is okay, but placing hands near the mouth can be unsafe since they are incapable of controlling their movements. Their mouths involuntarily convulse and they might end up biting your hands.

Emergency care is needed when the seizure lasts for five minutes or longer and when the incidence occurs twice successively. Even dogs already clinically diagnosed with epilepsy should still be checked by a veterinarian after the seizure. Other than its medical history, age and overall wellbeing of the dog are also critical factors. According to Dr. Zaidel, a New York-based veterinarian, older dogs are more prone to having seizures compared to the younger ones. Not a minute should be delayed if a 12-year-old dog experiences a seizure.

Weight Changes

Dr. Zaidel explained that a dog’s sudden loss of appetite can indicate gastrointestinal cancer. In this case, weight loss occurs so drastically that the caretakers cannot miss the physical change. The veterinarian at the Malta Animal Hospital even added that weight loss is among the sure signs of canine cancer, so immediate care should be given.

On the other hand, if your dog gains weight yet its appetite is poor, you should also be concerned. Dr. Timothy Rocha, a veterinarian oncologist based in New York, recommended a doctor’s visit in this case. Something unusual is going on inside your pet’s body. Feel the pouch of your dog. If the stomach appears to be bloated despite eating less food, your dog might have a swollen internal organ.

Related to weight loss or gain is the irregular bowel movement in dogs. Dr. Rocha explained that diarrhea should not be treated as a cancer sign right away. However, the possibility of it being an indicator of cancer is high if it drags on for weeks and worsens. Difficulty in urinating or defecating and vomiting should also be your warning signs. Blood in the urine or feces is highly unusual, thus emergency care should be undertaken by pet owners.

Persistent Coughing

Coughing and sneezing for a prolonged period of time indicate a serious respiratory ailment that necessitates expert care. It is possible for your dog to experience common colds from time to time. But if the coughing and sneezing continue despite medications, rest, and diet changes, these can be early warning signs of respiratory cancer. Shortness of breath after a brief or less tiring task is also indicative of a lung ailment, possibly even lung cancer. When there’s blood included in the mucus, you should not waste a second to have your beloved pet checked, lest its health rapidly deteriorates.

Early cancer detection in dogs can be tricky due to their inability to communicate with their caretakers in a clear language. However, being oriented with the signs discussed above will greatly help in the early diagnosis of canine cancers. When any or more than one sign shows up, consult your veterinarian right away. There must be no delaying of the doctor’s visit. Dogs may be exposed to the same range of cancers experienced by humans. But the cancer cells in dogs may metastasize faster than human cancer cells. Do not wait for your dog’s regular annual check-up; that may be too long a time to wait. Also, it is recommended to seek the second opinion of a veterinary oncologist to ensure an accurate and consistent diagnosis.

While there is no guarantee that your pet will or can survive cancer, the chances are higher if the disease is yet in its early phase. There are cancer types that do not show physical signs like brain tumor until the worst has happened already, thus observing your pet’s demeanor also helps. Unusual behaviors or any action outside their routines and habits should not be dismissed. Most importantly, trust your instinct. There is a special connection that dogs and their human owners share. If your instinct tells you something is wrong with your pet although all it manifests is plain weariness, then bring your pet to the doctor and do not self-medicate. For what it’s worth, your dog, your best pal, deserves the best care.


  1. Justin Palmer, From A Vet: 10 Early Warning Signs Of Canine Cancer – I Heart Dogs
  2. Dr. Phil Zeltzman, 10 Signs of Cancer in Dogs – Pet Health Network
  3. Sandy Eckstein, Dogs and Cancer: Get the Facts – WebMD Pets
  4. Dr. Kelly Ryan, Cancer in Pets – The Animal Medical Center of Mid-America
Dr. Travis McDermott

Dr. Travis McDermott is a small animal veterinarian that has been practicing for nearly 15 years in Las Vegas, NV. Dr. McDermott was born and raised in the great State of Texas and grew up on an emu farm raising chickens and pigs for 4H and FFA. He attended Texas A&M University for both undergraduate and DVM studies.After graduation in 2006, Dr. Travis McDermott started practicing at Tropicana Animal Hospital in Las Vegas, NV. In 2012, he took over as hospital director of Durango Animal Hospital – one of the largest veterinary hospitals in Las Vegas. Dr. McDermott treats dogs and cats as well pretty much any exotic animal that walks in the door. His interests include surgery, dental procedures, and ultrasound, but his main passion is endoscopy. Since becoming a veterinarian, Dr. McDermott has served as a board member and president/chair of both the Nevada Veterinary Medical Association and the American Veterinary Medical Association Political Action Committee and currently serves on the board of the Viticus Group (formerly Western Veterinary Conference).

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Note: The advice provided in this post is intended for informational purposes and does not constitute medical advice regarding pets. For an accurate diagnosis of your pet's condition, please make an appointment with your vet.