All cancers stem from abnormalities in DNA which are the “building blocks” of the cells

Cancer in companion animals is typically a disease of the elderly

There are many types of cancer

Treatment success frequently hinges on “catching it early”

What is cancer?

• Few words invoke as much of an emotional reaction as the word cancer (inter-changeable terms include neoplasia, malignancy and tumor). The term tumor is a general word for cancer whether it is benign (“good” cancer) or malignant (“bad” cancer).
  
• All cancers stem from abnormalities in DNA which are the “building blocks” of the cells. Your pet could have been born with a DNA abnormality that manifested later in life, or they could have developed the abnormality late in life and secondary to a number of poorly understood factors. There is speculation that certain chemicals and other environmental pollutants, as well as viruses can play a role in cancer development, however most of these are not definitively proven. Certainly, there is nothing that you have done to cause your pet’s cancer and there is nothing that you could have done to prevent it.
  
• Just like in humans, cancer in companion animals is typically a disease of the elderly. Due to better nutrition, better medical and surgical practices, leash laws, testing and segregating, vaccination programs and the animal-human bond, many pets are living significantly longer than they did 10 – 20 years ago.1 The older a pet becomes, the more chance there is for DNA damage and the more chance there is for cancer to develop.
  
• As a result, approximately 45 % of pets over the age of 10 years will develop cancer.2 Of the 74 million household dogs and 90 million household cats in the US, at least 4 million dogs and 4 million cats may develop cancer each year.3 
  

Types of cancer

• There are many types of cancer because tumors can develop within any tissue in the body. Malignant tumors have the ability to spread through the blood and lymph to other sites in the body far from the original site. This is called metastasis and typically causes most of your pet’s problems. Other malignant tumors lack the ability to spread to distant sites but can cause significant damage due to growth and invasion into local tissues. Tumors that do not metastasize and are not invasive are considered benign.
  
• There are three major categories of tumors in dogs and cats based on how the cells look under the microscope. Tumors that arise from glands and skin are called carcinomas, which form clumps or clusters under the microscope. Tumors that arise from tissue under the skin and not in the blood (connective tissue) are called sarcomas, which are elongated cells with tapered edges under the microscope. The final category is called round cell tumors because the cells are round under the microscope. Examples of tumors in each category are:
  
  • Carcinoma
    
    • squamous cell carcinoma (skin or gland tumor)
      
    • adenocarcinoma (gland tumor)
      
    • sometimes melanoma (skin or mouth tumor)
      
  • Sarcoma
    
    • osteosarcoma (bone tumor)
      
    • fibrosarcoma (connective tissue tumor)
      
    • hemangiosarcoma (blood vessel tumor)
      
    • peripheral nerve sheath tumor (nerve tumor)
      
    • leiomyosarcoma (smooth muscle tumor)
      
    • rhabdomyosarcoma (skeletal muscle tumor)
      
    • sometimes melanoma 
      
  • Round cell
    
    • lymphoma (cancer of the lymphocyte white blood cell)
      
    • mast cell tumor (cancer of the mast cell)
      
    • multiple myeloma (widespread cancer of plasma cell white blood cell)
      
    • systemic histiocytosis (widespread cancer of the histiocyte or macrophage white blood cell)
      
    • transmissible venereal tumor (sexually transmitted tumor)
      
    • sometimes melanoma
      

Signs

• The symptoms of cancer in companion animals are similar to those in people. Early detection is extremely important and treatment success frequently hinges on “catching it early”. Some of the most common signs of cancer are listed below:
  
  • Abnormal swelling that persists or continues to grow
    
  • Sores or wounds that do not heal
    
  • Unexplained weight loss
    
  • Loss of appetite
    
  • Bleeding or discharge from any body orifice such as the nose or mouth
    
  • Bad odor, especially from the mouth
    
  • Difficulty eating or swallowing
    
  • Reluctant to exercise or loss of stamina
    
  • Persistent lameness or stiffness
    
  • Difficulty breathing, urinating or defecating
    
  • Change in behavior
    
  • Excessive drinking and urinating
    
  • Persistent vomiting or diarrhea

Diagnostics

• Your oncologist will initially recommend testing to determine the extent of the tumor. This is called tumor staging and is important to determine your pet’s prognosis and help formulate a treatment plan.
  
• Testing usually includes blood tests (complete blood count and chemistry profile), urinalysis, radiographs (x-rays), tissue aspirate (inserting a needle into the area and drawing some cells from it) and/or biopsy (taking a small piece of tissue under anesthesia). In addition, and as indicated for specific patients, other testing may include abdominal ultrasound, endoscopy (direct visualization and biopsy of the esophagus, stomach, intestines or bronchi with a specialized scope), CT scan (three dimensional x-ray), MRI (magnetic resonance imaging), nuclear bone scan or bone marrow aspiration (inserting a small needle into the shoulder or hip bone and aspirating a small sample of marrow).
  
• It is important to realize that medicine is not an exact science and that despite these staging procedures, small sites of tumor that are difficult to study may not be detected. Once the tumor staging has been completed, we will be better able to discuss treatment options for you pet.
  

Treatment

• The timing of cancer therapy is critical for obtaining a remission. Many people assume that there are no treatment options available for companion animals with cancer and that their life is immediately over. This is typically not the case and while it may not be possible to cure your pet, we can certainly help make him/her feel better. Although some pets may experience transient discomfort from therapy, the vast majority have excellent quality of life throughout treatment.
  
• There are many treatment options available for companion animals with cancer. In general surgery and radiation therapy are reserved for local control (to remove or kill the primary tumor) and chemotherapy is utilized to prevent metastasis of the tumor, or for inoperable tumors. For some tumors treatment will consist of a single type of therapy, while combination therapy may be recommended for others.
  
• Tumors that have metastasized extensively are usually not curable, therefore, the objective of therapy for these pets is palliation (afford relief of symptoms and possibly prolong life without providing a cure). Localized tumors that are not deeply invasive have the best chance for cure.
  

*references are available upon request