What Is Cancer In Dogs?
"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.
Cancer is the result of abnormal cells multiplying out of control. These cells can spread throughout the body, leading to organ failure and death.
What Type Of Cancers Can Your Dog Get?
Cancer can occur anywhere.
The top five cancers in dogs are
breast cancer,TVT, 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. 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.
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.
Why Do Dogs Get Cancer?
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.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(warts).
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.
Common Symptoms Of Cancer In Dogs
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.
Dog Cancer Treatment
These days, there are several options available to treat dogs with cancer. Some dogs will be cured, and some will go into remission. However, for many dogs, the best we can hope for is an
improved quality of life and a bit more time with them. Caring for your dog with cancer can be very costly, because often more than one treatment type is needed. 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.
| Mammary Gland Surgery In The Dog |
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| This view is of the patient just prior to preoperative preparation of the surgical area for surgery. The large mass between the fourth and fifth nipple is evident. | The surgeon, employing sterile technique, begins the incision near the masses in the glands, being careful not to incise any tumor tissue. | Hemostasis (controlling bleeding) can be challenging in these surgeries due to the mass of tissue to be removed as well as the vigorous blood supply to the area. |
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| One side of the three mammary glands is dissected down to the abdominal wall; then the opposite side is dissected. | Care is employed to remove all the mammary gland tissue but also to leave enough normal tissue that closing the incision will not create excessive tension along the surgical closure. | Blood vessels are tied off and the row of three mammary glands is lifted away from the patient. Some veterinarians will remove all five glands even if no evidence of tumor in other glands is present. |
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| A major artery and vein to and from the area is the Caudal Superficial Epigastric vessels. Lymph channels drain from the last three mammary glands through this small channel through the abdominal wall. | After removal of the mammary glands (along with the tumor tissue) the incision is closed in layers from deep to superficial. The goal is to comfortably close the incision with no tension being placed on the skin. | In this case the skin is closed via two simple continuous sutures to decrease surgical and anesthetic time. The patient is placed on pain control medication for a few days and sutures are removed in 12 days. |
