Cancer

Cancer is an ugly word that no one wants to hear. There are many forms of cancer that can strike a dog, some rarer (prostate, uterine etc.) and some are more common (lymphoma, hemangiosarcoma etc.). According to some articles, 1 in every 3 dogs will get cancer (that's dogs, not just Golden Retrievers). By those stats we can see cancer is a very real concern. Equally as concerning, cancer knows no age, it can strike a dog at 16 years of age or at 2.

Lymphoma

Lymphoma is one of the most common cancers seen in dogs. Although there are breeds that appear to be at increased risk for this disease, lymphoma can affect any dog of any breed at any age. It accounts for 10-20% of all cancers in dogs.

Lymphoma (lymphosarcoma or non-Hodgkin's lymphoma) is a malignant cancer that involves the lymphoid system. In a healthy dog, the lymphoid system is an important part of the body's immune system defense against infectious agents such as viruses and bacteria. Lymphoid tissue normally is found in many different parts of the body including lymph nodes, liver, spleen, gastrointestinal tract and skin. Lymphosarcoma is classified according to the location in the body in which the cancer begins.

These include:

• Multicentric form occurs in the lymph nodes.
  
• Gastrointestinal form occurs in the stomach, intestines, liver and lymph nodes in the abdomen.
  
• Mediastinal form occurs in the mediastinum, in front of the heart in an organ called the thymus.
  Hence this form of lymphosarcoma sometimes is called thymic lymphoma.
  
• Cutaneous form occurs in the skin.
  
• Acute lymphoblastic leukemia occurs when the disease starts in the bone marrow.
  
• Miscellaneous forms of lymphosarcoma are less common and include those that begin in the
  nervous system, nasal cavity or kidneys.

Hemangiosarcoma

Hemangiosarcoma in dogs is an aggressive, malignant tumor of blood vessel cells. With the exception of the skin form of hemangiosarcoma, a diagnosis of hemangiosarcoma is serious. Because these tumors start in blood vessels, they are frequently filled with blood and when a blood-filled tumor ruptures, it can cause problems with internal or external bleeding.

Hemangiosarcoma can theoretically arise from any tissue where there are blood vessels, which is essentially anywhere in the body, but usually appear in the skin, soft tissue, spleen or liver with the most common site being the spleen. They are highly metastatic and will frequently spread to the brain, but also to the lungs, spleen, heart, kidneys, skeletal muscle and bone. This type of cancer in dogs is typically classified as dermal, subcutaneous or hypodermal, and visceral.

Mast Cell Tumors

Mast cells are specialized cells that are normally found throughout the body and help animals respond to inflammation and allergies. Mast cells can release several biologically active chemicals when stimulated which include histamine, heparin, seratonin, prostaglandins and proteolytic enzymes. Although these chemicals are vital to normal bodily function, especially immune response, they can be very damaging to the body when released in chronic excess.

Mast cell tumors (MCTs) (also referred to as histiocytic mastocytoma, mast cell sarcoma, mastocystosis (when there is systemic involvement)) are cancerous proliferations of mast cells that can spread throughout the body. The most significant danger from mast cell tumors arises from the secondary damage caused by the release of chemicals that they produce: gastric ulcers, internal bleeding, and a range of allergic manifestations. These tumors are the most frequently recognized malignant or potentially malignant neoplasms of dogs. MCTs may be seen in dogs of any age, but the average age is 8-10 years. There is no way to definitively identify MCTs without a biopsy and pathology report. It can be difficult not only to recognize mast cell tumors but to predict their course. They may be relatively innocent or aggressively malignant.

These tumors may develop anywhere on the body surface as well as in internal organs, but the limbs, especially the posterior upper thigh, ventral abdomen, and thorax are the most common sites. Location on mucocutaneous junctions or on the ventral surface of the body is associated with a more aggressive behavior. Many breeds appear to be predisposed, especially boxers, pugs, Rhodesian ridgebacks, and Boston terriers. The tumors vary significantly in size, shape, appearance and texture, but most commonly, they appear as raised, nodular masses that may be soft or solid which usually have dark granules in them. The granules contain substances which, when released, cause swelling, itching, and redness. Infrequently, when a large number of granules discharge their chemical contents into the bloodstream resulting in vomiting, stomach ulcers, shock and even death.

Osteosarcoma

Osteosarcoma (OSA) accounts for only approximately 5% of all canine tumors, but is by far the most common bone tumor of the dog. It is a malignant tumor of the bone and can develop in any bone, but most often occurs in bones bordering the shoulder, wrist and knee. Osteosarcoma of the limbs is called appendicular osteosarcoma and accounts for 75-85% of the cases of bone cancer. However, these tumors can also affect the axial skeleton (cranium, spinal column, ribs).

Osteosarcoma develops deep within the bone and becomes progressively more painful as it grows outward and the bone is destroyed from the inside out. Lameness may occur suddenly or start intermittently and progress over several weeks. Obvious swelling becomes evident as the tumor grows and normal bone is replaced by tumorous bone.

Tumorous bone is not as strong as a healthy bone and can break with minor injury. This type of broken bone is called a pathologic fracture. Pathologic fractures will not heal, therefore it is critical to diagnose and start treatment for osteosarcoma before this occurs.

Osteosarcoma usually occurs in middle aged or elderly large and giant breed dogs but can occur in a dog of any age with larger breeds tending to develop tumors at younger ages.

Highly aggressive and metastatic in nature, over 90% of all clinically significant osteosarcomas have already micrometastasized by the time of diagnosis. Most metastasis happens via menatogenous spread to the lungs and other bones, but lymph node metastases have been reported.

**To date (2011) there have been two dogs of our breeding who have been affected by what we consider early Cancer (diagnosed prior to 9 years of age). A 6 year old with lymphoma who passed away due to a pulmonary embolism (it is suggested due to the cancer), and a 5 year old with hemangiosarcoma who passed away.