Note: Part I of this two-part series on cancer in dogs, which appeared in the May-June issue of Mushing, covered lymphoma, mast cell tumors and osteosarcoma (bone cancer), the most frequently occurring cancers in dogs. These articles are meant to point the reader in the direction of the best treatment options available. Veterinary oncologists are most qualified to diagnose and treat cancer in dogs, or your veterinarian could conduct treatment in consultation with a specialist. Early detection is the key to success of therapy. If you notice fatigue, loss of appetite (an unusual symptom in a sled dog), limping, coughing, redness and/or swelling of the gums, lumps on a limb or other location, for which no explanation is found, cancer should be considered. Reproductive cancers such as mammary (breast) and testicular cancers, although almost non-existent in spayed or castrated dogs, are still of special concern to breeders. Spaying or castration should be a high priority for all dogs not meant for breeding, or after the last litter or stud service. If you think that a neutered sled dog will lose its “fire” for running, I never observed this in my dogs, and it is so delightful to live without the hysteria in the kennel when a female is in heat.Mammary tumors can appear as one or several nodules or large growths. The nodules may be small or large, soft or firm. Unspayed females between the ages of 5 and 10 years are most frequently affected. Males can develop mammary tumors as well, but this rarely occurs. The risk of mammary tumors in females spayed prior to their first heat is a mere 0.05%. The risk increases the longer you wait, i.e., to 8% after the first heat. Only about half of all mammary tumors are malignant. The latter grow rapidly, in contrast to the slow growing benign type. Malignant growths are characterized by irregular shape, firm attachment to the skin or underlying tissue, bleeding and ulceration. A final diagnosis of the type of tumor must be made by means of a biopsy before, or analysis of the tumor following removal. Tumors may metastasize (spread) to the lymph nodes into which the mammary glands drain – two axillary (in the armpit) and two inguinal nodes (inside the hind leg in the groin area). Drainage into these lymph nodes is what begins the spread of the cancer cells to other organs, such as the lung, liver and kidneys.Surgery is the treatment of choice in all except very old dogs. Recurrence largely depends on how early the tumor was detected and treated. Some veterinarians prefer to spay a dog in connection with surgery in the hope of decreasing recurrence, but there is no proof that this will be successful. Chemotherapy and radiation are not widely used in the treatment of mammary tumors in dogs, because this has not proven very successful in the past. However, since new drugs are being developed and treatment protocols are constantly improving, a veterinary oncologist should be consulted, so that the best possible treatment option can be considered. Mammary cancer is one of the most preventable cancers in dogs. If all females not intended for breeding were spayed before their first heat, this cancer could be practically eliminated. Testicular cancer is a common occurrence in older intact males. It very rarely occurs in younger dogs. Cryptorchids (dogs with one or two undescended testicles) are more likely to develop this type of tumor. Three types of this cancer are known. Many will produce estrogen (female hormone), resulting in enlarged mammary glands and nipples, hair loss, and anemia. The latter occurs due to bone marrow damage caused by estrogen, leading to a decrease in blood cell production. In a small number of cases metastases to the abdomen, lungs, or brain may occur. Castration is the treatment of choice for testicular cancer. Considering how easily this cancer could be prevented, all non-breeding males should be castrated at an early age. Benign or malignant tumors can arise in one or both anal glands. The malignant form, called apocrine gland adenocarcinoma of the anal sac, is highly aggressive and difficult to cure. If you observe scooting, difficulty defecating, or swelling at the site of the anal glands (located slightly below the anal opening on both sides), and notice blood in the stools, your veterinarian should conduct a rectal examination without delay. After ruling out an abscess, the next step is a needle aspiration or biopsy of the mass to confirm the cancer. This tumor can cause high blood calcium, which in turn leads to irregular heart rhythms and calcification of vital organs, i.e., the kidneys. Ultrasound and/or chest X-rays should be done to determine the possible spread to other sites, i.e., regional lymph nodes and lungs. Surgery is the recommended treatment, followed by radiation and/or chemotherapy, but this does not always prevent recurrence. Some dogs may experience post-surgical complications, i.e., fecal incontinence, which usually improves with time. Scar tissue and rectal strictures may cause discomfort. This can be eased with stool softeners. There is also the danger of infection due to wound contamination. In past studies chemotherapy alone has not proven successful. Unless blood calcium is excessively high, a dog may live up to a year without surgery. Older intact male dogs suffer the same prostate problems as do men, usually manifested by painful urination or defecation and a stiff gait. Prostate disease is characterized by an enlargement of the gland (benign prostatic hyperplasia) or infection/abscessation. Veterinarians diagnose an enlarged prostate gland by rectal palpation. In order to determine the possible presence of infection or cancer, urine is taken via a catheter after the examination, because it usually contains a greater number of cells from the prostate at that time. The urine sample is examined under a microscope. X-rays or ultrasound are usually recommended. A cancer diagnosis may be confirmed by biopsy.Although prostate cancer is generally considered to be rare in dogs, some experts believe that one in 150 medium to large breed dogs over the age of 8 years will develop this cancer. Its most common form is adenocarcinoma. The cancer rapidly spreads to bones, spinal cord, pelvis, lungs, kidneys, and lymph nodes. Surgery is not recommended, because the many vital nerves in this area decrease the chance of complete removal of the prostate. While it may be possible to achieve short-term remission or relief with chemotherapy and/or radiation, the prognosis is grave. The incidence of malignant melanoma in humans (there are also benign forms) has been extensively publicized in recent years, and this cancer occurs in dogs as well. Tumors can arise anywhere in the skin, usually as a dark mass, sometimes without pigment. The most important ones are those occurring in the mouth, mucous membranes in other parts of the body, and in the nail bed. According to Ruthanne Chun, DVM, Diplomate ACVIM (Oncology) and Clinical Associate Professor at the University of Wisconsin-Madison School of Veterinary Medicine, tumors appearing in these locations are highly invasive locally and spread rapidly to the lymph nodes, lungs and other organs. Most skin melanomas in dogs are benign. They can be removed surgically if they are causing problems due to their location, i.e., rubbing of harness. Most of the oral tumors, which constitute about 6% of all cancers in dogs, are located in the gums, but the lip and palate can also be affected. Predominant clinical signs are increased salivation, difficulty chewing, and loss of appetite. Swelling and ulcerating lesions may also occur. In addition to melanoma, squamous cell carcinoma and fibrosarcoma, which are often manifested as an ulcerated red spot, are considered the most important oral tumors. If detected and operated on early, the latter two have a good prognosis. If part of the underlying bone must be removed in order to completely excise the tumor, this may leave a cosmetic problem, but function remains normal.According to Dr. Chun, “Except for melanoma, the other oral tumors can be cured with surgery if identified early, one reason for good oral hygiene”. So keep your dogs’ teeth as clean as possible and look into their mouths frequently to spot trouble before it’s too late. Needless to say, all oral lesions should be sampled and examined under the microscope, even if they appear harmless. Don’t forget the pain factor. We all know how much any small lesion in the mouth hurts. Brain tumors are fairly rare and are more likely to affect older dogs. Disorientation and seizures are often the first signs observed. Tumors of certain structures of the brain can lead to personality changes, and sudden onset of aggression in a friendly dog should raise a red flag and prompt an immediate veterinary examination. Brain tumors are diagnosed by means of a CT scan or MRI. Surgery is usually not recommended for brain tumors. Seizures can be controlled with anti-seizure medications, such as Phenobarbital. Prednisone is prescribed to control inflammation around the tumor in order to decrease pressure on surrounding structures. Sedatives combined with behavioral therapy may be tried to control aggression, but euthanasia may be a wise choice, especially if there are children in the household. According to Dr. Chun, “Treatment for the majority of brain tumors is radiation, with survival time averaging about one year after diagnosis.”Stomach cancer (which can be manifested as lymphoma, adenocarcinoma or mast cell tumors) represents about 1 % of all cancers in dogs and usually occurs in individuals age 8 or older. General symptoms are vomiting, loss of appetite, distended abdomen and pain expressed by whining or yelping, especially when touched on the abdomen. According to Dr. Chun, “We are not usually able to alter the course of the disease much with surgery or chemotherapy, and this applies to other gastrointestinal cancers as well. Even if treatment were attempted, it would not be expected to extend the dog’s life beyond 6 months.”The prognosis of liver cancer can be favorable if the tumor resides in a single lobe, but grave if it involves the entire liver. Predominant symptoms suggesting extensive involvement include loss of appetite, anemia, increased thirst and urination, light colored stools, bleeding problems, a distended abdomen and signs of abdominal pain, yellowish mucous membranes and orange colored urine. You can help your dog best with a high quality supportive diet formulated by a veterinarian or veterinary nutritionist, but euthanasia is usually recommended.Contrary to humans, colon cancer is relatively rare in dogs. Other cancers, i.e., adenocarcinoma, can metastasize to the intestines. The symptoms are similar to those of colitis, i.e., bright blood and mucus in the stools, increased frequency of defecation, sometimes vomiting. Depending on the type of cancer, treatment may involve surgery plus or minus chemotherapy.Hemangiosarcoma, is a highly aggressive tumor arising from blood vessels. It occurs primarily in the spleen, liver, heart and skin. The internal form is usually diagnosed by palpation of a large mass in the abdomen, or sudden onset of weakness or collapse due to rupture of the tumor and bleeding into the abdomen. After confirmation by means of ultrasound and X-rays, surgery to remove the tumor is typically recommended, but, says Dr. Chun, “ Even with surgery and chemotherapy, most dogs succumb to the disease within 8-10 months of the diagnosis.”Years ago a 10-year-old Siberian leader of mine suddenly sat down while in harness and I loaded her into the sled. My veterinarian presumed heart failure and prescribed Lanoxin (digitalis). After two days without improvement, a veterinary internist performed ultrasound and diagnosed a hemangiosarcoma in the heart. The prognosis was considered too grave for surgery and the dog died the following day while I was still contemplating euthanasia. The skin form of hemangiosarcoma is less likely to be metastatic, and early surgical removal of these tumors combined with chemotherapy can be curative.A study in dogs with splenic hemangiosarcoma is presently in progress at the University of Wisconsin at Madison. The study evaluates the effects of CCNU, an orally administered drug that has demonstrated activity against a range of cancers. In a randomized trial CCNU will be compared to the anti-cancer drug doxorubicin. Treatment must begin within 14 days after splenectomy (removal of the spleen).More information about the study in hemangiosarcoma and other cancer studies ongoing at the University of Wisconsin Madison can be found at For information about studies at other universities, go to Google and type in: Clinical trials in dogs. New therapies are continually being evaluated. Particularly interesting are suicide gene therapy and vaccines. Numerous alternative treatments are also available, but sometimes testimonials are their only evidence of success. Solid proof of efficacy in many patients seems to be the wisest choice. If you choose to try an alternative treatment, do so only with the guidance of a holistic or integrative veterinarian.No one knows for sure what could prevent cancer, but it is advisable to avoid contact with environmental toxins such as gasoline fumes, farm and lawn chemicals and oil drips from vehicles absorbed by the footpads. Support your dog’s health and immune system with good nutrition. Always be vigilant for trouble signs, and if cancer is suspected or diagnosed in a dog of yours and you decide to just “wait and see,” then at least relieve the pain if necessary. Don’t let him hurt.


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