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Types of Cancer Cancer is an uncontrolled growth of abnormal cells on or within the body. Cancer may be benign (not malignant/self limiting) or malignant (tending to produce death/tumor characterized by uncontrolled growth, invasive). Cancer may also be localized or it may invade adjacent tissue and spread throughout the body. The first step to preventing cancer is awareness and early detection. Listed below are the main types of cancer found in canines. This resource is informational only and is not intended to take the place of a veterinarian diagnosis or to assist you in making a diagnosis for your pet. The most effective tool we have in fighting cancer is awareness and early prevention. Your pets life may depend on you being aware of these cancers. If you suspect your pet may have any aliment or if your pet is displaying any of the early signs/symptoms, please consult your veterinary physician immediately. This list appears in alphabetical order not in order of severity or prevalence Adenocarcinoma Adenocarcinoma Anal sac adenocarcinomas are tumors arising from the apocrine glands present on either side of the rectum. They occur primarily in older (average 10 years) female dogs; however, these tumors have been found in male dogs as well. Each sex has it's own syndrome. Dogs might have symptoms such as straining to have bowel movements (either due to the tumor itself or due to enlarged lymph nodes in the pelvic area), or the tumors might be found incidentally on a routine physical examination. Sometimes dogs may have symptoms such as increased drinking and urinating which results from very high calcium levels in the blood (due to hormones produced by the tumor) which in turn can affect the kidneys. Hermangiosarcoma Hemangiosarcoma is a very aggressive, high-grade soft tissue sarcoma with the most common areas affected being the spleen and heart. A highly malignant cancer which preys on blood vessels, it can spread rapidly, causing tumors almost anywhere in the body. Hemangiosarcoma is insidious, as it attempts to build it's own blood vessel network, making blood blister like formations which disrupts normal organ function. It is commonly in the advanced stage before detection, making it virtually a silent killer. A common form of cancer, hemangiosarcoma affects mostly older, large breed dogs though all dogs, including young, can be affected. Males tend to have a higher rate of diagnosis than females, with German Shepards, Golden Retrievers, Portuguese Water Dogs, and Skye Terriers, among others are effected more than other breeds. Lymphoma /Lymphosarcoma Lymphoma is one of the most common cancers seen in dogs. It is a cancer of lymphocytes (a type of blood cell) and lymphoid tissues. Lymphoid tissue is normally present in many places in the body including lymph nodes, spleen, liver, gastrointestinal tract and bone marrow. Most of the time, lymphoma appears as “swollen glands” (lymph nodes) that can be seen or felt under the neck, in front of the shoulders, or behind the knee. Occasionally, lymphoma can affect lymph nodes that are not visible or palpable from outside the body, such as those inside the chest or in the abdomen. In these cases, dogs may accumulate fluid in the chest that makes breathing difficult, or they may have digestive problems (diarrhea, vomiting, or painful abdomen). If left untreated, dogs with lymphoma will generally succumb to the disease within 3 to 4 weeks. The average dog with lymphoma is between 6-9 years although dogs of any age can be affected. Certain breeds (Boxer, German Shepherd, Golden Retrievers, Scotties, Westies and Pointers) may be more likely to develop this type of cancer. Males and females are equally at risk. In most cases, we cannot tell what causes the onset of this type of cancer. It is estimated that lymphoma occurs about 2 to 5 times as frequently in dogs than in people. 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 approximately 20% of all canine tumors, and less than 80% of cancers originating from blood cells. Mast Cell Tumor A common malignant tumor in dogs is the mast cell tumor. These tumors (also called mastocytomas) are the most frequently recognized malignant or potentially malignant neoplasms of dogs. In addition, leukemic and visceral forms can occur. Mast cells are immune cells that are responsible for allergies. Mast cells can be found in all tissues of the body but typically form tumors on the skin in close to 20 percent in the canine population. MCTs range from relatively benign to extremely aggressive, leading to tumor spread and eventual death. Particular breeds of dog are at risk for the development of this tumor, indicating a role for genetic factors. These tumors may occur in dogs of any age (average 8-10 yr). They may occur 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; approximately 10% are multicentric. Many breeds appear to be predisposed, especially Boxers and Pugs (in which tumors are often multiple), Rhodesian Ridgebacks, and Boston Terriers. The tumors vary markedly in size, and clinical appearance alone cannot establish a diagnosis. Melanoma Melanoma occurs commonly in dogs with pigmented (dark) skin. Melanomas arise from pigment producing cells called melanocytes, which are responsible for coloring the skin. Any dog can be affected, but Gordon Setters, Standard and Miniature Schnauzers, Doberman Pinschers, and Scottish terriers, among others, are at increased risk to develop melanoma, suggesting that this disease may have a hereditary component. Melanomas can occur in areas of haired skin, where they usually form small, dark (brown to black) lumps, but can also appear as large, flat, wrinkled masses. Melanoma of the haired skin in dogs is usually a benign tumor, although it can cause severe discomfort. In contrast, malignant melanoma, which develops in the mouth or in the distal limbs (usually the toenail beds), is an incurable disease. These tumors have very often spread to distant parts of the body (metastasized) by the time they are first noticed, making complete surgical removal impossible. Osteosarcoma Osteosarcoma is the most common type of primary bone cancer in dogs accounting for up to 85% of tumors that originate in the skeletal system. Osteosarcomas are highly aggressive tumors, characterized by local invasion/destruction and distant metastasis (spread to other organs). Osteosarcoma commonly affects the appendicular skeleton (limbs) of large to giant breed dogs, but can also occur in the axial skeleton (skull, ribs, vertebrae, pelvis), which is a more common primary site in smaller dogs. Large and giant breed dogs are at higher risk for bone cancer, especially of the long bones. For example, it is estimated that the relative risk to develop this disease in giant breeds such as Scottish Deerhounds and Great Danes may be as much as 200-times higher than in small and toy breeds. Among dogs at high risk, we also include Rottweilers, Great Pyrenees, Greyhounds, Mastiffs, and others. Osteosarcomas are seen most often in the appendicular skeleton (long bones of the limbs), most often “near the knee” and “away from the elbow.” However, these tumors can also affect the axial skeleton (cranium, spinal column, ribs). Large and giant breed dogs are at higher risk for bone cancer, especially of the long bones. For example, it is estimated that the relative risk to develop this disease in giant breeds such as Scottish Deerhounds and Great Danes may be as much as 200-times higher than in small and toy breeds. Among dogs at high risk, we also include Rottweilers, Great Pyrenees, Greyhounds, Mastiffs, and others. The disease usually becomes evident during middle age (~7-10 yr), although bone cancer can affect dogs under 1 year of age. Factors that affect growth rate, such as diets that promote rapid growth in puppies, also appear to influence risk. The tumors are very aggressive and metastatic, so it is a fair assumption that at the time of diagnosis the disease will have already spread beyond the primary site. The biological behavior, prognosis, and treatment of these tumors depends on tumor type, primary site (location), and extent of disease (stage). Therefore, various diagnostic tests such as radiographs (X-rays), bloodwork, and a biopsy are required to determine the most appropriate treatment. In dogs, approximately 50% survive one year with standard-of-care, less than 30% survive 2 years, and less than 10% reach 3 years. The signs associated with a bone tumor may be nonspecific and depend on the primary site. Tumors in the limbs often cause various degrees of lameness and pain, and a firm swelling may become evident as the tumor size increases. The pain can cause other problems such as irritability, aggression, loss of appetite, weight loss, whimpering, crying, sleeplessness, and reluctance to exercise. Tumors in non-weight-bearing bones may initially appear as a solid, firm mass. Other clinical signs may vary, depending on the primary site and involvement of underlying structures. Transitional Cell Transitional Cell Cancer (TCC) usually involves the neck of the bladder an area called the trigone. Both ureters from the kidneys dump their urine into the bladder in the trigone area. It is easy to understand why a mass in this location may cause a disturbance of urine flow. Many cases of suspected prostate cancer in dogs may actually be transitional cell carcinoma (TCC) of the urethra that is metastatic to the prostate. Pets often strain while trying to eliminate urine. They often urinate blood clots or blood stained urine. This activity appears or mimics a urinary tract infection, which can delay the discovery of this cancer. Antibiotics often create an apparent improvement. This masks the symptoms and further delays the diagnosis of this cancer. Finding a Veterinary Specialist Most small animal veterinarians are general practitioners-the earned their doctorate, passed the national and state veterinary licensing exams, and perhaps did a one year internship at a teaching hospital before entering private practice. But just as in human medicine, there are also veterinary specialists-vets who went on to study a particular area of medicine, such as cardiology, cancer treatment, or ophthalmology , in depth for several years after earning a doctorate. Veterinary specialists are usually found at a veterinary teaching hospitals or specialty centers rather then in neighborhood practices. When should you consult a specialist? Specialists are a terrific resource for vet general practitioners as well as for their clients and patients. Your vet will refer you to a specialist when your dog needs diagnostic tests or treatments that require special equipment or expertise, such as an MRI scan, cataract removal, or radiation therapy. A vet may also refer especially complicated cases to a specialist, sending a dog with a difficult-to-control seizures to a neurologist, or a dog with severe and persistent skin problems to a dermatologist. As your dog’s owner and health advocate, you can also ask your vet to refer you to a specialist. You may want to consult a specialist for a second opinion on treating a life-threatening illness or simply on clearing up a longstanding and vexing health problem. If you feel frustrated or uncertain about your dog’s illness, do ask your vet for a referral. That way your vet can send the specialist a summary of your dog’s previous treatment and test results to avoid confusion and unnecessary repetition of diagnostic procedures. Remember, though, that “vet hopping” is not the same as consulting a specialist. Taking your dog from general practitioner to another in the hope of resolving a health problem is expensive and unrewarding because each vet will have to start from scratch, and tests and treatments are bound to be duplicated. If you are truly dissatisfied with the medical problem, ask for the referral to a specialist for the immediate problem, and meanwhile search carefully for a new regular practitioner to provide regular routine care. Once you have settled on a new vet, ask your previous vet to send him a copy of your dog’s medical record and x-rays. The treatment-oriented specialties currently recognized by the American Veterinary Medical Association are dermatology; cardiology; neurology; internal medicine; oncology (cancer treatment); ophthalmology; radiology; surgery; behavior; dentistry; nutrition; and theriogenology (reproduction). To locate a specialist in your area, either ask your veterinarian for a referral (the easiest and best way) or search the websites listed below. American College of Veterinary Dermatology American College of Veterinary Internal Medicine American College of Veterinary Ophthalmologists American College of Theriogenologists American College of Veterinary Behaviorists American College of Veterinary Nutrition American College of Veterinary Radiology American College of Veterinary Surgeons American Veterinary Dental College
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