The following is part 1 of a 2-part series on the most frequently occurring types of cancer in dogs. The articles will provide some insight into this serious diagnosis and encourage you to continue searching for solutions and to consider all available treatment options before making a decision.I doubt that anyone with multiple dogs has been spared the diagnosis of cancer in one or more dogs. In the past, this was devastating. It meant saying goodbye to our furry friend soon. It no longer need be that way, because the many treatments now available to animals offer hope, the hope that it’s not over yet, and that there is still some quality time left for the dog.Numerous treatments are under study in addition to standard chemotherapy and radiation, i.e., gene therapy, vaccines, targeted therapies that destroy the cancer but preserve healthy tissue, even alternative treatments. Some treatments are abandoned during the study process because they do not keep their original promise, others eventually become available. Better diagnostic tests are also being developed. And, let’s not forget that all procedures and treatments are studied in countless research animals, from mice to rats to dogs, cats, pigs and primates, before they are allowed in human trials. So, animals deserve our gratitude for their pain and sacrifice, and it seems only fair that our dogs should benefit from the deaths of the thousands of their species that have died in the process of this research.Tumors (neoplasms) are either benign or malignant. Benign tumors grow by expansion and can therefore cause a lot of pressure, especially if in the brain. Malignant tumors destroy, invade, and spread (metastasize). The general symptoms of cancer are usually fatigue, anorexia (loss of appetite), weight loss, but there can also be many other symptoms, some general, some more specific to the different types of cancer, some painful, some painless. However, most of the symptoms of cancer mimic other diseases as well, which can be a pitfall for misdiagnosis. Some cancers cause no symptoms at first and may be discovered during the course of a general examination.Early detection of the condition is important for the success of therapy, so vigilance must be on top of the list for all of us. It goes without saying that no time should be wasted in starting treatment, especially for fast-growing cancers. Those who are concerned that the treatment may cause the dog too much discomfort should know that most dogs tolerate chemotherapy quite well.A second or even third opinion is advisable.Referral to a veterinary oncologist (cancer specialist) can be made by your veterinarian. If possible, a university clinic should be considered. The latter may offer the possibility of enrollment into a research study of a new medication or procedure. Prior to the start of a study, the protocol is reviewed by the Research Animal Resource Center (RARC) and/or Institutional Animal Care and Use Committee (IACUC). All aspects of the study are scrutinized before the study can begin. A dog owner must sign a consent agreement prior to entering the study, which explains the procedures, as well as the benefits and risks that may be incurred.One frequently encountered cancer in dogs – actually the third most frequently diagnosed – is lymphoma (lymphosarcoma). It is a cancer of lymphoid tissue which is present in lymph nodes, spleen, liver, gastrointestinal tract and bone marrow. Lymphoma can affect males and females of any breed and any age, but seems to strike 6-9-year-old dogs most frequently. It can be divided into different forms, the most common form involving external lymph nodes. Symptoms of lymphoma depend on the severity and location of the tumor(s), and whether organ function is affected, i.e., vomiting and diarrhea if the gastrointestinal tract is affected, or shortness of breath and muffled heart sounds if the chest (mediastinum) form is involved There is also a skin form of lymphoma, presenting with lumps in the skin or mouth, which may ulcerate and may be very bothersome to the dog. Or, the dog may have no symptoms or only exhibit fatigue. Often the only noticeable sign is enlargement of the lymph nodes, i.e., under the neck (mandibular node) or in the groin (inguinal node). If the cancer is limited to the bone marrow it is called leukemia, with its common symptoms of anemia, bleeding and infections. These symptoms are related to low numbers of blood cells – oxygen-carrying red cells, infection-fighting white cells, and platelets necessary for blood clotting. A complete diagnostic workup includes a general examination and history, CBC (complete blood count), chem. screen, lymph node biopsy, chest X-rays, abdominal x-rays and/or ultrasound to evaluate the liver and spleen. As to risk factors for lymphoma, some investigators have speculated that environmental factors such as exposure to pesticides or strong magnetic fields may be involved, but this has not yet been proven. These and other possible risk factors can be applied to other cancers as well.If they are brought to examination after considerable progression of the disease, untreated dogs with lymphoma may only have four to six weeks of life expectancy after diagnosis. If curative therapy is not planned, oral prednisone may be administered to reduce swelling and thus make the dog feel better during the short time left, but this is not expected to extend the dog’s life. According to the literature, if treated with chemotherapy, life expectancy may be a year or possibly longer, with good quality of life. If the dog does not seem to be suffering and still enjoys life, treatment would certainly seem worth considering. After all, a year of life in a young dog is said to equal 7 years of human life. According to Dr. Ruthanne Chun, Diplomate ACVIM (Oncology) and Clinical Associate Professor at the University of Wisconsin-Madison School of Veterinary Medicine, “On average, 4-8 new lymphoma patients come into the university clinic every week. About sixteen lymphoma patients receive therapy every week. “We see an average survival rate of around 12 months, with perhaps 25% of the dogs living 2 years and 12% living 3 years past diagnosis. We also have clinical trials in progress for this cancer.”Treatment of lymphoma consists of chemotherapy, such as cyclophosphamide, vincristine, doxorubiocin and prednisone. Depending on the treatment protocol this is usually a combination of oral and injectable drugs administered weekly. Treatment protocols are constantly being improved, and are best applied by a veterinary oncologist. Or, treatment could be conducted by a local veterinarian in consultation with a veterinary oncologist. According to Dr. Chun, “With a standard multi-drug chemotherapy protocol, about 90-95% of dogs go into complete remission (nodes go down to normal size, no detectable abnormalities on x-rays, ultrasound or bloodwork) for an average of 8-10 months. The dogs usually are on chemotherapy for 4-6 months, followed by monthly physical examinations until the tumor relapses (usually 4-6 months later). At that time the chemotherapy is repeated. This cycle goes on until the tumor becomes resistant to the initial chemotherapy protocols and even ‘rescue’ protocols. With this treatment regimen the average dog will have about 2 years of survival after the initial diagnosis.”Radiation and surgery are typically considered ineffective and impractical for lymphoma.A great number of tumors in dogs are manifested in the skin, and mast cell tumors (mastocytomas) – some benign, some malignant – constitute about 20% of these. Mast cells are part of the immune system, containing, i.e., histamine and enzymes. In addition to the skin they can occur in other areas, such as the intestines and respiratory tract. The skin tumors are most often found on the trunk, limbs and genital area. The malignant mast cell tumors represent one of the more serious and rapidly progressing forms of cancer in dogs. I lost two dogs (one Malamute, one Siberian) to mast cell tumors in the past. The progression of the disease was frighteningly rapid in both cases. Although mast cell tumors occur more often in dogs in the 8-9 year age range, they can affect dogs of any age. Any breed can be affected, but these tumors do appear to have a predilection for Boxers, Boston Terriers and other breeds with short wide muzzles. Although unproven, possible causes mentioned in the literature are environmental and hereditary factors, and even viral sources have been considered as possible causes.According to Dr. Chun, “On average, 2-6 new mast cell tumor patients are brought to the university clinic at Madison every week, with about 5-10 receiving treatment every week. I would say the majority of mast cell tumors are cured with appropriate therapy.”The first step in the diagnosis of mast cell tumors is usually a needle aspiration and examination of the cells under the microscope. This is Dr. Chun’s first step. A biopsy (tissue sample) allows analysis of the tissue rather than just a few cells. Two procedures called grading and staging, respectively, aid in the establishment of the diagnosis and course of therapy. Grade 1– a well differentiated tumor with slow cell division and low infiltration into surrounding tissues; grade 2 – moderate division and infiltration; grade 3 – tumor is poorly differentiated, rapidly dividing, and very infiltrative locally. Staging helps to determine how the tumor has spread from the primary site, which is usually to the regional and internal lymph nodes and other skin sites. Stages range from 0 to IV – comprising one to multiple small to large tumors, with or without lymph node involvement and/or metastasis in the skin. Removal of the tumor is the treatment of choice in most instances. If all of the tumor including a large portion of healthy tissue around the tumor is removed, this usually constitutes a cure of Grade I and 2 growths. If it is considered impractical or impossible to remove the tumor, radiation may be recommendedDr. Chun recommends further surgery to remove all of incompletely excised grade 1and grade 2 tumors or follow-up with radiation if complete excision is not possible, i.e., because the tumor is on a limb. If grade 2 tumors have spread to the nodes or if new tumors have recurred within weeks, chemotherapy is recommended. For all grade 3 tumors Dr. Chun recommends surgery to completely excise the tumor and follow-up chemotherapy consisting of a combination of vinblastine and prednisone in a 12-week out-patient regimen. “This is well tolerated and associated with long-term survival and good quality of life. If complete excision is not possible, radiation therapy provides excellent local control, preventing the tumor from recurring at the original site.”Bone cancer (osteosarcoma) occurs mostly in the large and giant breeds, and tends to be highly malignant and rapidly progressing. It usually appears at the end of long bones, but it can also occur in other bones, i.e., the skull. If the tumor occurs in a leg, swelling and lameness are easy to detect. However, if it occurs in other parts of the body, diagnosis is more difficult and can lead to a misdiagnosis of muscle strain or arthritis, especially since the first symptoms often appear after an injury. Although older dogs are more likely to get this aggressive cancer, it often appears in dogs one to two years of age, with a higher incidence in males.No one knows why dogs develop this cancer. One theory postulates that the fast dividing cells found at the growth plates in the bones have a genetically higher risk of mutation. By the time an osteosarcoma is diagnosed, 90% of these tumors will have spread to the lungs, although most of them will not show up on an x-ray at this time due to their initial small size. Other types of tumors can initially mimic osteosarcoma on an x-ray, thus a biopsy should also be done. Further, since fungal bone infections can have similar symptoms and appearance on x-rays, a fungal culture may be recommended as well.On average, 2-5 new osteosarcoma patients come to the clinic at Madison every week. After confirmation of the diagnosis, amputation of the affected extremity is usually recommended. In some instances limb-sparing surgery may be possible. According to Dr. Chun, “Limb-sparing surgery is a good option for dogs who cannot tolerate amputation because severe arthritis would make it impossible for them to walk without their fourth leg, or dogs who are already amputees. Limb-sparing surgery has about a 50% risk of chronic infection, which may be debilitating for the animal.Since metastasis still develops after amputation or limb-sparing surgery, chemotherapy (carboplatin, cisplatin or doxorubicine) is usually recommended following the amputation. A veterinary oncologist is the best source of knowledge of the newest chemotherapy protocols. The University of Wisconsin-Madison also has clinical trials in progress for this cancer. The life expectancy of a dog after proper treatment varies, but can be up to a year or longer. Heredity has not been proven, but for the time, it may be wise to regard any breed line where this cancer has occurred in a number of dogs with caution.Part II will deal with mammary cancer, testicular, prostate and anal gland cancers, hemangiosarcoma (a cancer arising from blood vessels), and others, including treatments and possible risk factors. We are confident that this dreaded disease will soon lose its deadly sting. So, when confronted with a cancer diagnosis, let a veterinary oncologist help you find the answers. And if you are already dealing with cancer in one of your dogs, insist on good pain management and anti-nausea medication if necessary. Last but not least – and this may be difficult in an anorexic or debilitated dog – find ways to deliver enough of the proper nutrients to support the immune system and maintain strength. Karen Gadke, PhD (Health Science) is a clinical study specialist, medical writer, author and lecturer. She has been mushing and racing since 1979. She owns both Siberian Huskies and Alaskan Huskies.


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