Health & Research: Cancer

Cancer is the leading non-accidental cause of death in dogs in this country. It is common in all breeds and the rate of cancer increases with age.

Cancer (also known as neoplasia) is caused by the uncontrolled, unrestrained growth of cells in the body. It cannot be considered as a single disease since cancer can arise from any tissue in the body, and some forms have the ability to spread (metastasize) throughout the body. Cancers can be very aggressive and spread rapidly, or they can be slow-growing and non-invasive. The cause of cancer in dogs, as in humans, is largely unknown, although there are many theories involving environmental factors, diet, vaccines, and genetic predisposition to specific forms of cancer. At this point, there is not enough conclusive evidence to point to any cause in particular.

Cancers fall into two basic categories:
  • sarcomas, which are derived from structural tissues such as bone, muscle, or cartilage, and     
  • carcinomas, which are derived from non-structural tissues such as blood, glands, and skin.

Despite its reputation, cancer is considered to be one of the most treatable of all chronic diseases, especially when detected early. The AVMA and the Veterinary Cancer Society have developed a list of 10 common warning signs:
  • Abnormal swelling that persists or continues to grow
  • Sores that do not heal
  • Weight loss
  • Loss of appetite
  • Bleeding or discharge from any body opening
  • Offensive odor
  • Difficulty eating or swallowing
  • Hesitation to exercise or loss of stamina
  • Persistent lameness or stiffness
  • Difficulty breathing, urinating, or defecating

If your Bullmastiff exhibits any of these symptoms, prompt evaluation by a veterinarian is imperative. Remember, if cancer is found early, it can be treated more effectively.
   
Diagnosis and Staging
Many tests and procedures are required to effectively evaluate the type and extent of the cancer. This process is known as staging. A CBC and chem-screen, urinalysis, and x-rays are the usual preliminary tests. Cytology (microscopic examination) may be performed on cells removed from a tumor using a small hypodermic (fine needle aspirate or FNA). A biopsy (evaluation of a small portion of a tumor by a pathologist, often involving  surgery and general anesthesia) will also aid in diagnosis. Other tests can include ultrasound, endoscopy, and specialized radiologic studies (CAT scan, MRI, etc.). These tests should provide sufficient information to determine the nature and extent of the cancer, and help the veterinarian assign a grade and stage to the tumor.

Grade: This refers to the pathologist's evaluation of the tumor's microscopic features. Tumors are often assigned a number such as grade 1, grade 2, or grade 3. Grade 1 would be a low-grade tumor while grade 3 would be a high-grade tumor. This information is useful in predicting how fast the disease might spread and how responsive the tumor might be to treatment; the higher the grade, the more aggressive it will be.

Stage: This refers to the extent of the tumor in the body, and the numbers assigned range from 1 to 5. A stage 1 cancer is small and localized, while a stage 5 has spread throughout the body.

Treatment
The three most common forms of treatment are surgery, chemotherapy, and radiation, and they may be used independently or in combination, depending on the type, grade, and stage of the cancer.

  • Surgery: Complete surgical removal is the standard form of treatment for most benign and some malignant cancers. Depending on the type, size, and location of the tumor, removal of all the tumor cells present may result in a cure. An excision with clear margins (no visible tumor cells at the edges) has the best prognosis. In some cases, a procedure known as debulking (partial removal of the tumor) is used to remove as much cancer as possible while minimizing damage to the surrounding tissues. This form of surgery is usually used in conjunction with other therapies. As with any other surgical procedure, there are risks associated with general anesthesia, and there will be some post-operative care required. Testing and re-examination are vital to monitor for the recurrence of cancer.
  • Radiation: Radiation is a treatment option that works well on localized disease. Usually, it is employed after surgery if there are still tumor cells present, or it may be employed before surgery or chemotherapy to shrink a tumor. Radiation, at several thousand times that used for normal x-rays, harms rapidly dividing cells. Because the radiation does not differentiate between normal cells and cancerous cells, there are some side effects that, while unpleasant, are usually not serious. Radiation dermatitis (resembling a severe sunburn) may develop at the site; hair loss and color change are common. The therapy usually extends over several weeks, and anesthesia is necessary since the dog must be perfectly still during treatment, and there is always a slight risk associated with general anesthesia. The goal of radiation therapy is to completely eradicate the tumor, and this sometimes occurs. Often, though, the tumor remains but its growth is inhibited. Frequent follow-ups and re-evaluation are important.
  • Chemotherapy: Chemotherapy may be the sole treatment for some cancers (especially systemic cancers or those that have spread) or may be used in combination with other therapies for high-grade, localized tumors. For the most part, chemotherapy is used to improve the quality of life by minimizing discomfort caused by a tumor or slowing the progression of the disease. The medications used in human oncology are the same as those used for treatment of canine cancers. Some are oral medications that can be administered at home, others are given via injection, while some require hospitalization for slow infusions, and treatment may be for a few brief weeks or lifelong. These drugs act against cells in the process of growth and division, but they are unable to distinguish between normal cells and cancerous cells, so some side effects are seen with chemotherapy. However, the damage done to the normal cells is rarely permanent. Because lower doses are used in dogs, they experience fewer side effects than humans. These side effects typically involve some gastrointestinal upsets and suppression of bone marrow, but most Bullmastiffs do not experience hair loss. Medications are available to minimize the known side effects, and most dogs complete a course of chemotherapy with little discomfort. Continued re-evaluations are, of course, indicated in any cancer treatment program.

Newly developed therapies
  • Hyperthermia: This is a method of treatment involving the use of a heating device to raise the temperature of a tumor, and it is used in combination with other therapies such as radiation or chemotherapy.
  • Cryosurgery: This is most useful in the treatment of small, benign tumors of the skin and involves freezing the tumor cells with liquid nitrogen.
  • Photodynamic: This process involves administering a special drug that is then activated by a laser light source that releases free radicals to cause tumor death. Because the laser can only penetrate a few millimeters, this treatment is limited to superficial tumors.
  • Palliative Radiation: Also known as comfort care improves the quality of life for dogs in which a cure or long-term control of the cancer is not possible. It is particularly useful in alleviating pain from bone cancer when combined with anti-inflammatory and pain medications. Side effects are similar to those mentioned above in the discussion of radiation.
  
Pain and Cancer
Bullmastiffs are notorious for their high pain tolerance and stoic nature. It is extremely important to be alert for any changes in behavior that might indicate pain. Some dogs may appear depressed or dull while others may become tense or agitated, changing position frequently or even refusing to lie down. Unusual vocalization can indicate pain, as can rapid or shallow breathing. Often, dilated pupils and eyes that are wide open also signify pain. Behavioral changes such as increased aggression, unusually submissive behavior, or a relentless quest for attention may also indicate that the dog is suffering. Careful observation of the patient is extremely important.
    
Assessing the Treatment Options
Aggressive treatment of cancer is not an option for every patient or every owner. Treatment can be very costly and the time commitment can be overwhelming; therapy may need to be continued for the remainder of the dog's life. The goal of therapy is to keep the patient as comfortable as possible, preserve the dog's quality of life, and possibly conquer the cancer. These goals are not attainable in every instance, and treatment is sometimes ineffective.
    
Euthanasia
Euthanasia is a very personal and very difficult decision. Naturally, the efficacy and feasibility of treatment options must factor into this decision, but the overriding concern must be for the dog. Explore all of the options available, and carefully evaluate exactly what therapy can realistically offer. The decision not to treat is every bit as important and valid as the decision to pursue therapy. Euthanasia is a painless end to the suffering and misery that your Bullmastiff may be experiencing, and is the final gift you can give.
    
Types of Cancers Commonly Found in Bullmastiffs
  • Lymphoma (or Lymphosarcoma) is a cancer of the lymphocytes (a kind of white blood cell) and usually originates in the lymph nodes, spleen, or bone marrow. Enlargement of the dog's lymph nodes is often the first indication of illness, but be aware that there are also other explanations for swollen lymph nodes and cancer is not always the diagnosis. A biopsy or a fine-needle aspirate is necessary, in conjunction with blood tests, to determine the specific cancer and to develop a treatment program.
  • Chemotherapy can be effective against this particular form of cancer, often resulting in a remission as long as 8-12 months. However, the prognosis for long-term survival is not good.
  • Hemangiosarcoma is a highly malignant, rapidly spreading cancer of, in the simplest terms, the blood vessels. The organs most often involved are the spleen, heart, liver, and lungs, although hemangiosarcoma can occur in the skin as well. Despite advances in treatment using chemotherapy, and although surgical options are sometimes helpful, survival rates are very low. In many instances, the dog will exhibit no symptoms at all until the tumors rupture, causing acute hemorrhage and sudden death.
  • Mast Cells are a type of blood cell that is part of the body's response to inflammation and allergens. These cells can become cancerous and develop into tumors, and these tumors have the capacity to spread to other organs. Mast cell tumors are most commonly found in the skin or subcutaneously, though the spleen, liver, lymph nodes and bone marrow are other common sites.
  • Biopsy and blood work (including a "buffy coat smear" to test for mast cells circulating in the bloodstream) are useful in the initial evaluation of the mast cell tumor, and grading is used to try to predict the potential for metastasis.
  • In the case of low-grade tumors, surgical excision may be the only treatment required. If the tumor is high-grade or if clear margins cannot be attained, additional treatment involving radiation and/or chemotherapy may be recommended.
  • The prognosis for tumors that have already spread or that occur in places other than the skin is guarded. However, for cutaneous mast cell tumors in an early, localized stage, where there is no systemic involvement, the prognosis is excellent. Early detection and excision can result in a complete cure.
  • This particular cancer is very common in Bullmastiffs. It cannot be emphasized strongly enough that immediate attention to any and all lumps and bumps found on your dog is crucial.
  • Osteosarcoma most often affects large- and giant-breed dogs and carries a very poor prognosis. These are highly aggressive and invasive tumors. Pain and swelling in a limb are usually the first signs of the disease, though certainly both of these symptoms can be attributed to far less serious diseases as well. Diagnosis is made by x-ray and biopsy coupled with a complete physical examination.

Surgical removal of the affected area, if possible, combined with chemotherapy may increase the survival rate, but often palliative care to eliminate pain and symptoms is the only viable treatment.

Mammary tumors are the most common form of tumor in an unspayed female dog, and they are closely associated with exposure to estrogen in the early years of development. Early spaying can significantly reduce the likelihood of developing mammary tumors later in life.

It is recommended that all mammary gland masses be surgically removed and biopsied. Many are benign and are successfully treated through surgery alone, while the malignant forms pose a risk for both recurrence and metastasis.

Bitches not intended for breeding should be spayed at an early age. Any lumps or bumps should be immediately removed and biopsied since, as with mast cell tumors, early detection and treatment are critical to long-term survival.

Resources
The most comprehensive internet resource on canine cancer is OncoLink, a service provided by the Veterinary Hospital of the University of Pennsylvania, and the bulk of the information contained herein was garnered from this website. For in-depth discussion of canine cancers, visit http://www.oncolink.com/, visit the site map, and click on "Veterinary Oncology".

See also:

For Help with the Nutritional Aspects of Cancer Treatment:

This information is provided for educational purposes only and is not a substitute for medical advice. It is not to be used for diagnosing or treating a health problem, nor is it a substitute for professional care. If you suspect that your dog may have a health problem, please consult your veterinarian.