Causes & Misconceptions

Causes of cancer in dogs:

1)    Hormones affect the risk of mammary cancer. Spaying female dogs prior to their first heat significantly reduces the risk of mammary cancer and spaying in general eliminates the possibility of ovarian and uterine cancer.

2)    Neutering male dogs eliminates the possibility of testicular cancer, but hormones do not affect the risk of prostate cancer, which is different compared to men.

3)    Dogs exposed to an herbicide named 2,4 – dichlorophenoxyacedic acid (2,4-D) have higher odds of developing lymphoma than dogs not exposed. This herbicide is commonly used in lawn care especially on golf courses.

4)    Osteosarcoma occurs most commonly in large breed dogs and in the metaphaseal area of long bones. Large breed dogs > 80 lbs are at greater risk as are taller dogs. Dogs that grow quickly and are very active during those growth spurts are at higher risk. The theory is that strenuous activity leads to microfractures in rapidly dividing cells causing damage to DNA that can lead to cancer later in life. Small breed dogs are not as commonly affected because their growth plates close earlier and there is not as much weight on the bones to cause microfractures.

5)    Other causes of osteosarcoma include hereditary, previous fracture especially if repaired with a metallic bone plate and irradiation. The occurrence of cancer caused by fracture repaired with bone plates is relatively very low and may occur a few months to 10 years later. The occurrence associated with previous irradiation is also very low (<1%) and occurs 3 to 5 years after irradiation.

6)    Intranasal cancer in dogs: long nosed breed dogs living in a smoking household have a two-fold higher risk of developing intranasal cancer.

7)    Lung cancer in dogs is rare. Second hand smoke in the household can cause lung cancer in dogs and the short nose breeds have a higher than two-fold higher risk of developing lung cancer due to second hand smoke than other causes, whereas long nosed breeds did not. This together with the risks of nasal cancer in ling-nosed breeds enforces the explanation that the extensive nasal turbinates in the long-nose breed filter many of the air-borne carcinogens.

8)    Viruses can cause cancer in dogs and cats, but not always. Many dogs and cats that have cancer causing viruses do not develop cancer. Some of these viruses are: papillomavirus in dogs and feline leukemia virus, feline immunodeficiency virus, feline sarcoma virus and feline syncytium-forming virus (feline foamy virus) in cats.

9)    Sunlight is a commonly known cause of squamous cell carcinoma on the nose and ears of white cats.

Common misconceptions:

1)    “Cancer can not be cured.”  Many of the cancers in pets can be cured. Typically surgery alone or surgery plus radiation therapy are required. Dogs and cats are very stoic and typically recover from surgery quickly and handle radiation therapy side effects with relative ease.

2)    “Chemotherapy causes severe side effects.” Chemotherapy is typically well tolerated in pets. Some pets don’t have any effects. Most pets will have mild effects that are self limiting. It is uncommon for pets to have severe or fatal side effects from chemotherapy. The side effects from chemotherapy are the same effects as in humans, but the severity of these effects is significantly less than in humans.

3)    “Pets don’t feel pain.” Pets feel pain by the same mechanisms as in humans. If a pet is limping, he/she is painful. It is, however, difficult in some situations to determine when a pet is painful. Signs of pain can be described as anything out of the ordinary. Increased heart rate, limping, and yelping when pain is elicited are obvious signs of pain. More difficult signs can be excessive vocalizing in quiet dogs or excessive quietness in vocal dogs and hiding in dogs that typically enjoy attention or increased attention seeking in independent dogs. Excessive licking, self trauma and fear biting can be signs of pain.

4)    “I don’t want to put my pet through it.” Although treatments typically have side effects, pets tend to be very resilient and stoic. Side effects or recovery that may seem severe to us as humans are actually well tolerated by pets. Amputation for example has a relatively quick recovery time in pets. This may be due to the fact that amputation in pets consists of an excision through soft tissue, whereas in humans the same surgery will involve cutting through bone leaving a stump on which a prosthetic limb can be worn. It is rare for amputation in pets to result in a stump. Recovery from excision through soft tissue is less painful than through bone. Additionally, amputation due to bone cancer or severe fracture, immediately takes away a tremendous source of pain.