The Newsletter of Dwight – Pine Bluff – Lakewood Animal Hospitals
May 2005

FOCUS ON: CANCER

It is a word that strikes fear into all of us.  It brings images of suffering and death, and we fear the treatment as much as the disease. Many of us don’t really understand what cancer is or what causes it.   We hope this issue will answer some of your questions and give you a better understanding of that dreaded disease, cancer.
 
 

What is “Cancer?”

Cancer is a generic definition.  In reality, there are hundreds of different types of cancer, ranging from a localized skin tumor to invisible but deadly internal organ destruction.  But regardless of the type or location of cancer, the same basic biologic processes cause the disease.
Briefly, “cancer” refers to the uncontrolled growth and spread of abnormal cells.  All of our cells, all the time, are continually replicating and dying.  New cells are produced, old and damaged cells destroyed.  In the healthy animal, this process is carefully balanced: cell death roughly equals cell reproduction.  Furthermore, our cells are differentiated: although all our cells contain the DNA to produce an entire new organism, most of the DNA is “turned off” and the cell is only allowed to perform specific functions: thus, a liver cell produces bile acids, while a skin cell grows hair but cannot turn into a liver.
 In cancer, this cycle of cell replication, differentiation, and death becomes unregulated.  Uncontrolled growth occurs, and cell death does not happen “on schedule,” leading to development of a tumor.  In addition, tumor cells are often undifferentiated, meaning they lose normal cell function.  They also can break off the original tumor and spread to other body organs, a process called metastasis.  Many tumor cells have the ability to monopolize nutrients, allowing further growth of the tumor at the expense of the rest of the body.
What Causes Cancer?
Basically, cancer starts from a single cell that has undergone genetic mutations that alter the normal control mechanisms of growth and reproduction.  Many different things can cause malignant mutation.  Environmental toxins, such as cigarette smoke and ultraviolet light, are well-known initiators of DNA damage that can lead to cancer.  Some pets, just like humans, may be genetically prone to cancer.  And while most cancer is not considered to be contagious, there are some viruses that can cause damage DNA and lead to cancer.  Feline leukemia virus is a well-known viral cause of tumors in cats.
 Unfortunately, our understanding of what causes cancer remains very limited, and that means it is difficult to prevent cancer.  Eliminating environmental toxins (for instance, pets can be harmed from secondary cigarette smoke), spaying/neutering your pet at a young age, keeping your pet in ideal health and providing excellent nutrition are the best preventive measures.

Treating Cancer

There are three main methods for battling cancer, no matter the type: surgery, chemotherapy, and radiation.
 When a tumor is localized in a site where it can be removed, surgery is often the first and best treatment.  Complete surgical removal can dramatically prolong survival or even cure the cancer.  Because many tumors spread microscopically, wide margins of apparently healthy tissue are removed around the tumor whenever possible.  Biopsy is used to diagnose the type of tumor and to determine if the tumor was completely resected.
 Chemotherapy is the administration of drugs designed to destroy the tumor.   Chemo drugs attack rapidly reproducing cells.  In most cases, the cancer cells are the fastest growing in the body.  However, other cells with rapid growth include the bone marrow, GI tract, and hair – hence immune suppression, nausea, and hair loss are common side effects of chemotherapy.  Fortunately, pets rarely experience the severe side effects that humans suffer.  Most owners are amazed at how well their pet handles chemotherapy.
 Radiation therapy is another method of destroying surgically inaccessible tumors.  Radiation is also used to provide pain relief for inoperable tumors such as brain and bone cancer.  Radiation therapy requires multiple or prolonged visits to a referral institution with specialized equipment, and therefore can be very expensive.
 Because whole body health is very important to give a pet the best chance at fighting cancer, basic care is also critical.  Ensuring optimal nutrition, adding supplements as indicated, regular exercise, and pain relief are all essential for your pet’s well-being.

Common Animal Cancers

Hemangiosarcoma: Hemangiosarcoma is a cancer of the blood vessels.  It occurs most commonly in the spleen.  Large-breed dogs such as Golden retrievers and German shepherds are at highest risk.  This is a devastating cancer because it is rarely detected until an advanced stage.  The most common symptom is sudden weakness when the tumor ruptures and bleeds internally.  Emergency surgery is needed to save the pet’s life.  Hemangiosarcoma spreads rapidly and has often metastasized by the time of diagnosis.  Even with surgery and chemotherapy, hemangiosarcoma is often fatal within just a few months of diagnosis.
Lymphoma: This very common cancer of the lymphatic system affects the entire body.  In dogs, the external lymph nodes enlarge, and owners often detect lumps in the throat or the groin.  In cats, lymphoma most commonly occurs in the intestinal tract, and loss of appetite, vomiting, and diarrhea are common symptoms.  Lymphoma usually responds dramatically to chemotherapy and is therefore a rewarding cancer to treat.  Pets often enjoy disease-free remissions of 1-2 years.
Mast cell tumor:  The most common malignant skin tumor in dogs, this appears as a skin mass that may be red, raw, or itchy.  Without a needle aspirate, it may be difficult to distinguish a mast cell tumor from a benign skin mass.  Surgical removal cures most cases of mast cell tumor.  However, some tumors are aggressive and grow back or spread to other locations; these cases are often fatal.
Transitional cell carcinoma (bladder cancer): Symptoms of bladder cancer mimic a common urinary tract infection: straining, frequent urination, and blood in the urine.  A bladder ultrasound will detect the tumor.  These tumors are often not removable surgically and tend to spread or recur.  However, they are usually slow-growing, and dogs may live several years after diagnosis.  Oral and injectable chemotherapy can further minimize symptoms and prolong survival.  Studies have indicated that frequent use of lawn chemicals may put pets at higher risk for bladder cancer.


 
 

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