Cancer in Dogs

The most common types of cancer in dogs are mammary cancer, skin cancer, mouth cancer, bone cancer, and cancer of the lymphatic system.

If your dog is diagnosed with cancer, it will be a real shock to your system. However, if you know more about the disease and how it will affect your dog, you'll be able to “keep your head about you”, to quote Rudyard Kipling, and make the best decisions for your beloved pet.

Cancer develops when cells divide abnormally. All cells divide, but this is carefully controlled by genes – some genes are responsible for starting the process of cell division, and others stop it. Damage to these genes may result in uncontrolled cell division, which is cancer.

Let's look at each one a little closer...

5 Common Types of Cancer in Dogs

1. Dog Mammary Cancer

Most cases of mammary cancer in dogs occur in middle aged females. Spaying a female dog before their first estrus virtually eliminates the risk of this disease, so it is most common in dogs that haven't been neutered, or who had this surgery when they were already mature. It is fairly easy to detect – you'll be cuddling your dog, or rubbing her tummy, and you'll notice a firm lump near her nipple. These lumps grow quickly, and they may ulcerate on the top. Mammary cancer tends to spread to the liver and lungs and it often has a poor prognosis.

2. Dog Skin Cancer

While there is a risk of squamous cell carcinoma in white dogs that love to lie in the sun, the most common skin cancer in dogs is the mast cell tumor. This often occurs during middle age in short coated breeds such as the Staffordshire Bull Terrier, but there is a suggestion that it is hereditary in the Golden Retriever and Labrador Retriever. These tumors start out as small lumps on the skin, but they may grow quickly and ulcerate on top. They can also spread to internal organs. Mast cell tumors are graded from I to IV, with grade I tumors having the best prognosis.

3. Mouth Cancer

Often the first indication that your dog has a tumor in their mouth is that they have difficulty eating, or their saliva becomes blood stained. Oral types of cancer in dogs are aggressive, and often spread to the jawbone. These tumors aren't usually noticed until they are well advanced, so the outcome of treatment isn't good.

4. Bone Cancer, or Osteosarcoma

Dog Bone CancerBone cancer (osteosarcoma), is a disease of large breed dogs such as German Shepherds, Greyhounds and Newfoundlands. Some research papers suggest that it is hereditary in some breeds. This cancer usually develops on the bones near the knee, and on the long bones of the foreleg. One of the earliest symptoms of osteosarcoma in dogs is a limp, and a swelling on the bone. Some dogs don't show any signs until the cancerous bone breaks, because it is so weak. Unfortunately, osteosarcoma spreads to the lungs very quickly, and is usually well established by the time it is diagnosed. Dogs with this disease often don't live much more than two years after diagnosis, even with treatment.

5. Lymphatic Cancer

Lymphocytes are white blood cells that are an important part of your dog's immune system. They can become cancerous, and this disease particularly affects their gastrointestinal tract, bone marrow, skin and lymph glands. Symptoms vary depending on where the cancer has occurred. Intestinal lymphosarcoma can present as an intestinal obstruction with vomiting and weight loss. If the disease has infiltrated the lymph nodes, they will be firm and swollen. There have been reports of several dogs from the one family being affected by lymphosarcoma, which suggests that it may be genetic in some individuals. Treatment of lymphosarcoma in dogs often doesn't result in a cure, but it is possible for affected dogs to go into remission for many months. While they are in remission, they show no signs of cancer, and appear perfectly well.

Diagnosing Cancer in Dogs

Cancer in DogsSome cancers are easy to diagnose. Your dog may have a lump on their skin, or on their mammary gland, and a biopsy reveals cancer cells. Others are more tricky. For example, lymphosarcoma in the bone marrow is often associated with anemia and a low white cell count, which may cause very vague signs of illness. If an organ is cancerous, it can't do its job effectively, so the first sign of a problem is organ failure. One example of this is with kidney cancer; affected dogs initially show general signs of kidney disease such as extreme thirst, and weight loss.

Blood tests are often taken as part of the diagnostic process. These tests are looking for changes in the blood count that can indicate that your dog's bone marrow has been affected, or any sign that their internal organs aren't working properly.

Ultrasound can help to confirm or deny a suspicion of cancer in internal organs, but it can really only be proven by biopsy. Cells are taken from a suspicious lump, or from an organ or bone marrow, and looked at under a microscope. Malignant cells have certain characteristics such as an obvious increase in the rate of division, and irregularities of the cell structure.

Treating Canine Cancer

Your veterinarian may refer your dog to a veterinary oncologist (cancer specialist) for treatment. They have advanced training and more experience in treating cancer in dogs, which may result in a better outcome for your four legged best friend.

The aim of all cancer treatment is to destroy or remove the tumor cells, while leaving the remaining body tissues unaffected. This isn't always possible.

Many tumors are initially treated with surgery. Dogs with osteosarcoma usually have the affected leg amputated, to remove the main tumor mass and to ease their pain. Mast cell tumors are also removed, but with these tumors, a wide area of normal skin should be removed from around the lump.

Dog Chemotherapy Side Effects

Dog ChemotherapyChemotherapy is also used to treat cancer. Drugs such as vincristine, cyclophosphamide and doxorubicin specifically kill cells that are rapidly dividing, so are very useful in treating cancer cells. Unfortunately, they also affect normal healthy cells that are rapidly dividing, such as those in the bone marrow and in the gastrointestinal tract. This means that common side effects of chemotherapy are vomiting, diarrhea and a lowered immune system. Dogs don't seem to lose their hair with chemotherapy like people do.

Radiation therapy uses beams of radiation to kill cancer cells, but it too affects normal cells, leading to side effects like those of chemotherapy. The advantage of radiation therapy is that the radiation beam can be tightly focused, to minimize the effects on nearby tissues.

Supportive Care for Canine Cancer

While your dog is undergoing cancer treatment, it's important to do everything you can to support their body. This means making sure they are eating well, and keeping them free of parasites. Many people like to use natural therapies to help their dog fight their illness. If your veterinarian isn't experienced with natural therapies, they will be able to refer you to a colleague with more experience.

In many cases, treatment won't cure your dog's cancer, and will only give you a bit more time with them. Palliative care, including dog pain relief and fluid therapy, will support them and keep them comfortable until it is time to let them go.

Treatment for cancer in dogs is expensive, and the prognosis often isn't favorable. There are many options for treatment, with different costs, side effects and results. Your veterinarian will help you to make the best choices for you and your dog, so that you both get the best possible outcome.

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