"Your dog has cancer". These words are guaranteed to strike fear into the heart of any dog owner. It's an alarming diagnosis, but knowledge is power. If you know more about the disease process, you'll better understand what's likely to happen to your dog, and how best to treat him.
In a nutshell, cancer is abnormal cell division and multiplication. That may sound a bit confusing, but it's fairly straightforward. Cells in all organs of the body grow and divide as part of their normal life cycle. The division of a cell results in two cells, hence the term "multiplication".
Cell division is fairly rapid in young growing pups, to allow for the increase in body size. As dogs reach adulthood, this cell division slows and stops, until only cells of the skin, bone marrow and intestine continue to divide throughout life. The body keeps a close check on the balance between cell multiplication and cell death, so there is always just the right number of cells in an organ. This balance is controlled by genes - there are genes which switch on cell division, and some that switch it off.
There are two factors that contribute to the development of cancer. Firstly, damage to a cell's DNA can affect the genes involved in controlling the rate of cell division. Secondly, the body for some reason loses its ability to kill cells with damaged DNA. The result is abnormal cells multiplying out of control. These cells can spread throughout the body, leading to organ failure and death.
The top five cancers in dogs are breast cancer, bone cancer, skin cancer, cancer of the mouth, and cancer of the lymphatic system.
As you'd expect, breast cancer is most common in female dogs, but it does also occur in males. This tumor usually occurs in middle aged to older dogs, particularly if they are not spayed, or were spayed as a young adult. This is because the hormones associated with the heat cycle can trigger abnormal growth of the mammary cells.
The symptoms are hard to miss - firm, irregular lumps or masses can be felt under or near a nipple. The lumps usually appear in the mammary glands between the back legs. They grow rapidly and can develop smelly ulcers on top. Veterinarians rely on a biopsy to confirm that it is indeed cancer. Sometimes the lumps are benign, but there is a real risk that these benign lumps will turn cancerous over time. It may be a good idea to remove the lump before it becomes dangerous.
Treatment for this type of dog cancer is surgery to cut away the lump, and chemotherapy. If the dog hasn't been spayed, then this is also done, to remove the hormones that may trigger a recurrence of the cancer. Unfortunately, in many dogs, by the time breast cancer is diagnosed, it has already spread to the internal organs, and the outcome is not good.
Osteosarcoma is the most common bone cancer in dogs, and it is not a nice disease. It tends to occur in middle aged, large breed dogs, and it most often develops at the ends of the long bones of the leg. As you'd expect, the first indication that there is a problem is usually when the dog starts to limp. The limp progressively gets worse, and a painful swelling may develop where the tumor is growing. The cancerous bone isn't as strong as normal bone, and it may suddenly break.
A veterinarian can usually make a diagnosis based on the dog's age and breed, and an xray of the sore leg. However, a bone biopsy will give a definite answer. Bone cancer is extremely painful, and by the time it is diagnosed, it has usually already spread to the lungs. Treatment commonly involves amputation of the leg. Most dogs do very well with only three legs, and they feel better with the painful tumor removed. Chemotherapy can extend their life, but many dogs with osteosarcoma don't survive past one year, even with treatment.
Many people associate skin cancer with too much time in the sun. That's also true in dogs, but the most common skin cancer in dogs isn't related to sun exposure at all. It's called a mast cell tumor, and they usually appear as fast growing ulcerated nodules on the legs or body. They can be aggressive and spread to the internal organs. It's important that when these tumors are removed, that a wide margin of normal skin is taken too. With radiation and chemotherapy, dogs with mast cell tumors can enjoy a good quality of life for several years.
There are many different types of tumor that can develop in a dog's mouth and throat. They all cause similar symptoms: bad breath, pain and difficulty eating, and sometimes bloody saliva. Most tumors aren't found until the disease is fairly advanced, so it's a good idea to regularly look inside your dog's mouth.
These tumors can spread into the bone of the jaws, and treatment often includes surgical removal of part of the jaw. Although dogs do seem to cope with this, it can make eating more difficult. This is often followed up with radiation therapy to try and increase survival time. As with the other cancers we've discussed, these tumors don't have a good prognosis, with many dogs not surviving for much more than a year after diagnosis.
Lymphocytes are cells which are produced in the bone marrow, and are part of the body's immune system. As with any other type of cell, they too can become cancerous. This is called lymphoma. When they do become cancerous, they can damage any organ that has lymphatic tissue. There are four common areas where lymphoma develops - the lymph nodes, the gastrointestinal tract, the bone marrow and the skin. Symptoms vary depending on which part of the body is affected, but in most cases, dogs will also vomit, stop eating and develop a fever.
Without treatment, dogs with lymphoma only survive a few months after diagnosis. Chemotherapy can lead to remission in most cases, where the signs of cancer disappear, and the dog is essentially normal. Remission can last for as much as a year, but the cancer often reappears.
There are four main influences in the development of cancer in dogs, and some of them can be managed to reduce the risk of the disease. Let's look at them one at a time.
1. Genetics: There are genes that have been identified in some breeds of dog that seem to increase the risk of them developing cancer. German Shepherd Dogs often develop hemangiosarcomas (a tumor of blood vessels), whereas osteosarcomas are common in Rottweilers. The fact that some types of tumors are more common in certain breeds suggests that these tumors have a genetic basis.
We've already mentioned that tumors develop due to damage to DNA. It's also possible that a dog is born with damaged DNA in his cells.
2. Infection and inflammation: Papilloma virus usually causes harmless growths in a dog's mouth. However, there appears to be a link between papilloma virus infection and the tendency for a dog to develop aggressive cancer of the mouth.
Chronic inflammation of an area may also trigger the growth of cancer. One example of this is when a broken limb has been repaired with plates and screws. If the screws become loose over time, then the irritation to the bone may lead to osteosarcoma in the area.
3. Hormones: There are very strong links between hormones and breast cancer in dogs. Spaying a female dog before their first heat virtually eliminates the risk of breast cancer later in life. However, if she is spayed after 2 years of age, spaying doesn't protect her at all. Similarly, a tumor known as a perianal adenoma (a tumor of the tissue around the anus) is much more common in entire male dogs.
4. The environment: In people, there have been connections made between exposure to pesticides and the development of cancer. There doesn't appear to be as strong a link between environmental toxins and cancer in dogs, so this may not be such an important influence. It does appear that being exposed to tobacco smoke may increase the risk of cancer of the nose and sinuses. Sun damage can lead to skin cancer in dogs.
While we can't always prevent our dogs developing cancer, there are steps we can take that will reduce the risk. Female dogs should be spayed before their first heat. Male dogs with an undescended testicle should be neutered, because the retained testicle is more likely to become cancerous. Dogs with thin hair coats and pale skin should not be allowed to sunbathe. If you are going to buy a dog of a breed which has a higher incidence of cancer, choose the parents carefully, so you've got the best chance of avoiding any genetic cancers in your dog.
Look for areas of swelling. An example is osteosarcoma, where the tumor causes swelling on a leg. Cancer may also appear as a wound or ulcer that doesn't heal. Squamous cell carcinoma of the skin causes raw areas on pale hairless parts of the body , and mast cell tumors form little ulcerated nodules on the skin.
It's often easy to notice abnormalities on the outside of our dogs, but many cancers grow in internal organs. These cancers can cause vague symptoms of ill health, include weight loss, drinking to excess, or vomiting or diarrhea. Perhaps an elderly dog just doesn't seem to be doing well. That's also a good indication that you need to visit your veterinarian for a checkup.
If you do notice anything abnormal, make an appointment with your vet sooner rather than later. Cancer treatment in dogs usually has a better outcome if it is started early, so getting a quick diagnosis is crucial.
The most obvious first choice is surgery, if possible. Removing a tumor can relieve pain and make dogs more comfortable. It can also mean that other therapies, such as radiation, are more successful because there are fewer tumor cells left to kill.
Chemotherapy involves using drugs to kill tumor cells. The idea is to kill the dangerous cells while leaving normal cells unharmed. The drugs do this by specifically attacking rapidly growing and dividing cells. Because there are normal cells in the bone marrow and intestine that are also dividing quickly, they can be affected by the chemotherapeutic drugs. This can lead to side effects such as vomiting and diarrhea for a few days after treatment.
Radiation therapy involves using a focused radiation beam to kill tumor cells. It too can affect rapidly dividing normal cells, so veterinarians try and protect surrounding parts of the body as much as possible. They also spread out radiation treatments to allow normal cells to recover.
Some dog owners like to use alternative and natural therapies to support more conventional treatment. Many vets now offer these services, and they may improve the outcome for some cancer patients.
While a dog is undergoing these stressful procedures, there are things you can do to support him through it. Good nutrition is so important to keep up his energy levels. If his appetite is poor, he may need to be fed through a stomach tube. He may need fluids to stop him becoming dehydrated, and in most cases he will definitely need pain relief.
It's quite okay to make the decision not to treat your dog with cancer. If treatment isn't likely to be very effective, or if the cost is beyond the family budget, you may want to consider hospice care. With the support of your vet, you can take care of most of his needs at home. You can learn to give fluids under the skin, and give him medication to keep him free from pain. The ultimate goal of hospice care is to give your dog a good quality of life for as long as possible. If his quality of life isn't good, it may be time to consider euthanasia.
In addition, advances in veterinary care mean that dogs are living longer than in the past, and the incidence of cancer is therefore increasing. It's quite possible we'll have to deal with a diagnosis of cancer in our beloved dog at some time in our lives.
New diagnostic tests and treatment choices mean that the outcome for many cases of cancer in dogs is quite good. Work with your vet, choose your treatments carefully, and you'll get the best outcome possible for both you and your dog.
Some other pages you may be interested in:
What is the best dog food?
More dog health care articles.
Please consult the services of a Professional Dog Trainer, Behaviorist or Veterinarian before implementing any of the advice contained on this site.