You might not be worried about your dog getting cancer at some point in his life, but unfortunately, it might happen. In fact, cancer is the leading cause of death in dogs over the age of 10. Fifty percent of dogs over the age of 10 will develop cancer at some point. Therefore, it’s best to be prepared in case your pup does develop the unfortunate disease at some point in his lifetime.
What is Dog Cancer?
Cancer, regardless of the species in which it occurs, is the uncontrolled growth of abnormal cells. Cancer cells develop because of damage to DNA. Dogs can inherit damaged DNA, which accounts for some hereditary cancers. More often, though, a dog’s DNA becomes damaged by exposure to something in the environment, such as carcinogens.
Not all tumors are cancerous. Benign (noncancerous) tumors are common and do not spread to other parts of the body. With very rare exceptions, they are not life threatening. Malignant tumors, however, can spread (metastasize) to other parts of the body, where they begin to grow and replace normal tissue. Regardless of where a cancer spreads, it is usually named for the place it began.
Common Forms of Cancer in Dogs
There are dozens of different types of dog cancer, but there are several that are the prime offenders. Here’s a brief overview.
Hemangiosarcoma in dogs is an aggressive, malignant tumor of blood vessel cells. A diagnosis of hemangiosarcoma is serious, with the exception of the form of hemangiosarcoma that occurs in the skin. These tumors begin in blood vessels and are frequently filled with blood. When they rupture, it can cause problems with internal or external bleeding.
Hemangiosarcoma can theoretically arise from any tissue where there are blood vessels, which is almost anywhere in the body. They most commonly appear in the spleen, but are also often found in the skin, soft tissue, or liver. Hemangiosarcomas are often highly metastatic and will frequently spread to other organs and even bones.
Lymphoma (lymphosarcoma or non-Hodgkin’s lymphoma) is a malignant cancer that affects the lymphoid system. Lymphoma specifically refers to a diverse group of cancers in dogs that are derived from white blood cells called lymphocytes. These lymphocytes exist in the lymphoid system and normally function as part of the immune system to protect the body from infectious viruses and bacteria. Between 15 and 20 percent of malignant tumors in dogs are lymphomas.
Lymphoma can affect virtually any organ in the body, but mostly affects organs that function as part of the immune system. Lymphoid tissue is found in many parts of the body, including the lymph nodes, spleen, liver, gastrointestinal tract, skin, and bone marrow. Lymphosarcoma is classified according to the location in the body in which the cancer begins.
There are over 30 types of canine lymphoma, and these cancers vary greatly in their behavior. The five main types of lymphoma are multicentric (lymphoma affecting external lymph nodes), mediastinal (lymphoma involving organs within the chest, such as lymph nodes or the thymus gland), gastrointestinal (lymphoma of the stomach and/or intestines), cutaneous (lymphoma of the skin), extranodal (lymphoma affecting the chest, skin, liver, eyes, bone or mouth) and central nervous system. Multicentric lymphoma is by far the most common type of lymphoma in dogs.
Some forms of lymphoma in dogs progress rapidly and are life-threatening without treatment, while others progress very slowly and are managed as chronic, inactive diseases. But if left untreated, the cancer can be aggressive and lead to a high mortality rate.
Mast Cell Tumors
Mast cell tumors in dogs are the most common skin tumors. Roughly one third of all tumors in dogs are skin tumors, and up to 20 percent of those are mast cell tumors.
Mast cell tumors are cancerous proliferations of mast cells. Mast cells reside mainly in the skin, but are also plentiful in other parts of the body, such as the intestines and lungs. These cells fight against parasitic infection, help repair tissue, form new blood vessels, and are also connected to allergic reactions. Mast cell tumors invade and impair these functions and affect heart rate, blood pressure and more.
Although mostly found in the skin, MCTs can and will spread throughout the body, commonly appearing in the spleen, liver, and bone marrow. The danger from MCTs comes not from the tumors themselves, but the secondary damage caused by the release of chemicals that they produce.
Mast cell tumors are sometimes referred to as “the great imposters,” because there is no way to definitively identify them without a biopsy and pathology report. Although they are most frequently found on the trunks and limbs of dogs, MCTs can vary widely in their size, shape, appearance, texture, and location. Not only are they difficult to recognize, but it is also nearly impossible to predict their course. They can also range in their threat level from completely benign to aggressively malignant.
Since MCTs are so common in canines, it’s important for any dog owner to have a basic understanding of what they are and the threat level they pose to your dog.
Same as with people, malignant melanoma affects pigmented cells known as melanocytes. Most malignant melanomas occur on the mouth or mucous membranes, although about 10 percent are found on parts of the body covered with hair. This cancer tends to grow extremely fast and is likely to spread to other organs, including the lungs and liver.
Squamous Cell Carcinoma
Squamous cell carcinoma is a cancer that originates in the outer layer of a dog’s skin. Cutaneous squamous cell carcinomas are typically fast growing tumors that get bigger with time and resist healing. As carcinomas are malignant and particularly invasive, it is essential to have this form of dog skin cancer diagnosed and treated without delay.
Squamous cell carcinoma is often caused by exposure to the sun. Studies also show a possible connection between the papilloma virus and the development of squamous cell tumors in certain dogs.