FETCH would like to recognize Texas A&M University, College of Veterinary Medicine, and the University of Pennsylvania, Matthew J. Ryan Veterinary Hospital for contributing content for our list of frequently asked questions.
Some of the causes of tumors are known, but much is not yet understood. Some factors that cause tumors include viruses, parasites, irradiation (sunlight, x-rays), hormones, genetic predisposition, and some chemicals. Neoplasia is common in pet animals and the incidence increases with age. Cancer accounts for almost half of the deaths of pets over 10 years of age. Dogs get cancer at roughly the same rate as humans, while cats get fewer cancers.
Skin – Skin tumors are very common in older dogs, but much less common in cats. Most skin tumors in cats are malignant, but in dogs they are often benign. Your veterinarian should examine all skin tumors in a dog or cat to determine if any are malignant.
Mammary Gland (Breast) – 50% of all breast tumors in dogs and greater than 85% of all breast tumors in cats are malignant. Spaying your female pet before 12 months of age will greatly reduce the risk of mammary gland cancer.
Head & Neck – Neoplasia of the mouth is common in dogs and less common in cats. Signs to watch for are a mass or tumor on the gums, bleeding, odor, or difficulty eating. Since many swellings are malignant, early, aggressive treatment is essential. Neoplasia may also develop inside the nose of both cats and dogs. Bleeding from the nose, breathing difficulty, or facial swelling are signs that may indicate neoplasia and should be checked by your veterinarian.
Lymphoma – Lymphoma is a common form of neoplasia in dogs and cats. It is characterized by enlargement of one or many lymph nodes in the body. A contagious feline leukemia virus can be the cause of lymphoma in some cats.
Testicles – Testicular tumors are rare in cats and common in dogs, especially those with retained testicles (testicles that did not move to their normal positions during growth, and may be located in the abdomen or between the abdomen and scrotum).
Abdominal Tumors – Tumors inside the abdomen are common but it is difficult to make an early diagnosis. Weight loss or abdominal swelling are signs of these tumors.
Bone – Bone tumors are most often seen in large breed dogs and dogs older than seven years, and rarely in cats. The leg bones, near joints, are the most common sites. Persistent pain, lameness, and swelling in the affected area are common signs of the disease.
Many of the above signs are also seen with non-neoplastic conditions but they still need prompt attention by a veterinarian to determine the cause. Neoplasia is frequently treatable and early diagnosis will aid your veterinarian in delivering the best care possible.
Most people are very surprised to learn that dogs and cats have a higher incidence of many tumors than we do. Dogs have 35 times as much skin cancer as we do, 4 times as many breast tumors, 8 times as much bone cancer, and twice as high an incidence of leukemia. The only types of cancer that are more frequently seen in humans than in small animals are not surprising: lung cancer is 7 times higher in humans, and stomach/intestinal malignancies are 13 times more frequent in humans than in dogs and cats.
Several breeds that are known to have higher incidence of tumors including Boxer, Golden Retriever, Rottweiler, and Bernese Mountain Dog. And these dogs seem to develop cancer at an earlier age than dogs of other breeds. Other breeds with a notably high incidence of cancer are the Boston Terrier, English Bulldog, Scottish Terrier, and Cocker Spaniel. Breeds with a relatively low incidence of cancer include the Beagle, Poodle, Collie, and Dachshund. Why do some breeds have a high incidence of cancer while some are rarely affected by it? If we knew the answer to that question, we would undoubtedly be closer to preventing cancer than we are. Probably the answer will come through the study of molecular biology and genetics; many of these dogs have probably inherited (or acquired through mutation) abnormal genes that predispose them to cancerous transformation of cells.
Some types of tumors are more prone to develop in one type of dog than in others. For example, the giant-breed dogs like the St. Bernard and the Great Dane have a much higher incidence of osteosarcoma (a very malignant bone tumor) than does the general canine population. White cats, cats with white on their faces, and dogs with white hair and thin skin are prone to develop carcinomas in their skin due to long-term exposure to the ultraviolet rays of the sun. Black dogs have a comparatively high incidence of melanomas, or pigmented skin tumors. The female dog that is not neutered has 7 times the risk of developing mammary tumors as compared to the dog that is neutered early in life. This fact indicates that, as is the case in human females, the hormones estrogen and progesterone are potent stimulators of breast cancer in the dog.
Neoplasia is often suspected on the basis of the pet’s medical history and physical exam. Additional tests, such as radiographs (x-rays), blood tests, and ultrasound exams, may be necessary to confirm neoplasia. A biopsy, taking a tissue sample from the neoplasm for examination under a microscope, is usually necessary to confirm the diagnosis and help determine if the neoplasm is benign or malignant. Additional biopsies of other tissues, such as lymph nodes, may be necessary to determine how far a malignant neoplasm (cancer) has spread.
Unfortunately, veterinary research has not come as far as research in humans in this area. Certainly, most dogs and cats with cancer are middle-aged to older animals, but the exact effect of an animal’s age on the incidence of cancer is not well understood. In general, cancer is thought of as a disease of advancing age — as cells continually divide through the progression of life, there is an increased chance of genetic mutation due to cell division “accidents” and to the actions of carcinogens (cancer-causing agents) on DNA. Asbestos, nickel, cadmium, uranium, radon, vinyl chloride, benzidene, and benzene are well-known examples of carcinogens that may act alone or along with another carcinogen, such as cigarette smoke. It is clear that some people are more sensitive than others to factors that can cause cancer, and this is probably the case in animals as well. Also, depression of the normal immune response in the older animal may play a part in the increased incidence of cancer seen with advancing age.
The more we can learn about what causes cancer in both humans and animals, the more likely we will be to find ways to prevent it. Epidemiologists study patterns of disease in the population to look for factors that affect the risk of developing these diseases, including cancer.
Actual causes have been identified for only a few tumorsof animals. The transmissible venereal tumor in the dog is spread by implantation of cells during breeding, and the canine oral papilloma (“warts”) of young dogs is caused by a virus. In cats lymphoma (cancer of the lymph nodes) has been proven to be caused by a virus. In man, several forms of lymphoma have been shown to be of viral origin as well, but no virus has as yet been recovered from lymphoma in the dog. Squamous cell carcinoma in white cats, white dogs, in Hereford cattle (which have white faces), and on the faces of horses with white facial markings, especially around their eyes and on their noses, has been shown to be caused by ultraviolet (UV) radiation from the sun’s rays.
Dogs that “sunbathe” on their backs, exposing their relatively hairless groin region to sunlight for hours, are very prone to develop squamous cell carcinoma over the skin over their abdomen. The sun’s UV rays are strongest during the summer from about 11 a.m. to about 4 p.m. The risk from exposure to the sun is greatest at this time, too, when the sun is high overhead and shadows are short. As a rule, it is best to keep animals out of the sun during these hours if possible. Recently, certain vaccines have been found to cause sarcomas in a small number of cats at the site of vaccination; research is ongoing to determine which cats are most likely to be affected and to make vaccines that do not lead to malignant transformation of cells.
Some other known risk factors can be avoided; for example, neutering female dogs before their first heat cycle nearly eliminates the risk of mammary cancer. Other risk factors, such as those that are inherited, are unavoidable.
As mentioned in the incidence of cancer above, certain breeds or bloodlines of dogs or cats may also have a much higher incidence of certain kinds of cancer than is normal for the species. It is not always clear whether a pattern of cancer in a human or animal family is due to heredity, factors in the environment, or just to chance. Still, if close relatives of your pet have been affected by cancer, or if your veterinarian informs you that the breed of your particular dog or cat is at high risk for developing some specific type of cancer, it is important to follow your veterinarian’s advice to avoid any predisposing causes for that cancer type, if they are known.
Have regular check-ups performed by your veterinarian so that, if the cancer develops, it is likely to be found early.
Advances in veterinary care have made many cancers treatable and capable of being put into remission, or possibly cured, while preserving the animal’s quality of life. Not all cancers are curable, and different types of cancer respond to different treatments in different ways and with different levels of success. There are many different options, depending on the type of cancer, where it is located, and how advanced it is. Each type of neoplasia requires individual care and may include one or a combination of treatment options such as surgery, chemotherapy, radiation, cryosurgery (freezing), hyperthermia (heating) or immunotherapy (stimulation of the immune system to fight disease). Surgery and radiation therapy are important in the treatment of local disease (for example, a focal mass or masses), whereas chemotherapy and immunotherapy are important in the treatment of systemic disease (for example, a cancer that was systemic to begin with like lymphoma, or a focal cancer that has metastasized or spread to other organs). Additionally, palliative (reducing the severity of the disease) treatments may be available that do not affect the spread or progression of the cancer, but may improve your pet’s quality of life by reducing pain or improving function.
Hopefully, all malignant cells can be removed by the surgical method before any spread occurs to other organs. With some tumors, however, re-growth either occurs rapidly or surgical resection (removal of part of an organ or structure) is impossible due to the location or extensiveness of the cancer. In these instances, radiation therapy is the best option, presuming that the particular cancer cells are radiosensitive. Chemotherapy is used if there is disseminated disease or if the surgically removed cancer is likely to have spread microscopically to other organs. Hormonal therapy may be useful in tumors that are hormonally-dependent, such as breast cancer or prostatic (prostate) neoplasia. In some cancers, immunotherapeutic treatment using vaccines, anti-tumor antibodies, or drugs which can modulate the immune system may be useful. When your veterinarian is deciding on the best combination of therapies for your pet, he or she will take into account all the information discovered during the tumor workup and staging. Your pet’s overall health is important too, and your veterinarian may recommend dietary changes or other things to help your pet better respond to treatment. Once you have a diagnosis, your veterinarian will discuss the best treatment option(s) for your pet and the risks and side effects associated with each option. Pain management is also an important part of treatment. In some instances, your veterinarian may refer you to a board-certified oncologist (cancer specialist) and/or specialty clinic depending upon the recommended course of treatment.
Some types of neoplasia can be cured, but other types can only be managed to decrease spread and prolong your pet’s comfort and life as much as possible. How early a neoplasm is detected and the type of neoplasm are often the biggest factors determining the success of treatment. You are encouraged to obtain a referral to a Board-certified Veterinary Specialist from your family veterinarian whenever possible. This ensures the proper transfer of medical information and is beneficial to the Veterinary Specialist, and will help your companion animal receive the best care possible.
Success of treatment strongly depends upon the type and extent of the neoplasia, as well as the aggressiveness of therapy. Benign neoplasms are usually easier to treat, and treatment of any type of neoplasia is more likely to be successful if the neoplasms are detected early. Although some neoplasms (especially the more aggressive cancers) cannot be cured, treatment can prolong your pet’s life and improve their quality of life.
Animals today have a better chance of being successfully treated for neoplasia and cancer than they did ten years ago, and the more we learn about it, the more pets’ lives we can improve and save.
New diagnostic methods can help detect neoplasia earlier and improve your pet’s chances, and new treatment methods are being developed to provide better success rates with less risk of side effects.
There are several types of Board-certified Veterinary Specialists who work together to treat cancer. Specialists are veterinarians who, after graduating from veterinary school, seek additional focused training in certain areas. This training usually lasts an additional 3-4 years (one year of internship, and 2-3 years of residency, depending on the specialty). At the end of this training, the Specialist must pass a certifying exam. Veterinary specialists trained to treat cancer include medical oncologists, radiation oncologists, and surgeons.
A veterinary medical oncologist is a veterinarian who specializes in the overall diagnosis and treatment of cancer, and will usually administer chemotherapy. Medical oncologists are Board-certified by the American College of Veterinary Internal Medicine (ACVIM). Their credentials will usually read “Diplomate ACVIM – Oncology”. For more information, including a searchable database, please visit http://www.acvim.org.
A veterinary radiation oncologist is a veterinarian who specializes in the treatment of cancer with radiation therapy. Radiation oncologists are Board-certified by the American College of Veterinary Radiology (ACVR). Their credentials will usually read “Diplomate ACVR (RO)”. For more information, including a searchable database, please visit www.acvr.org.
A veterinary surgeon is a veterinarian who specializes in surgery. Veterinary surgeons are Board-certified by the American College of Veterinary Surgeons (ACVS). Their credentials will usually read “Diplomate ACVS”. Some surgeons have a special interest in surgical oncology, however there is currently no formal certification for surgical oncology as a subfield. For more information, including a searchable database, please visit www.acvs.org.
After a cancer diagnosis, your medical oncologist can suggest, based on your pet’s condition, what the best treatment protocol is, which may include surgery, chemotherapy, and/or radiation, as discussed below.
Your first resource is your family veterinarian (general practitioner) who knows you and your companion animal well. Your family veterinarian can help obtain the diagnosis, help inform you about the disease, and offer treatment options and/or referral to the appropriate Board-certified Veterinary Specialist.
Dogs and cats seem to tolerate anesthesia, surgery, radiation, and chemotherapy more easily than people. Also there are many different treatment options used for your companion animal with cancer. The goal is always to cure the cancer if possible, but in many veterinary patients, a complete cure may not be possible at the time the disease is diagnosed. In this case, the goal of treatment is to put the cancer into remission and lengthen your companion animal’s life while providing a good quality of life. Our pets’ lives are too short to allow them to feel poorly for any length of time before we switch to another treatment protocol. There certainly can be complications associated with surgery, chemotherapy or radiation therapy, but many are mild and self-limiting, and most companion animals tolerate the process well. The specific things you might expect your companion animal to experience vary with the treatment and any underlying conditions your companion animal might have, and should be discussed in advance with your veterinary oncologist. Learn what your options are, and how your veterinary oncologist thinks your companion animal would respond! You may be surprised at how good your companion animal feels during the treatment.
Surgery is important for the removal of “gross” or solid/visible disease, and is most useful in the treatment of a single, discrete mass. The goal of cancer surgery is usually to remove not only the visible mass, but a rim of normal tissue around it — this amount varies with the type of cancer. The reason for this is that some tumors will extend microscopic “fingers” of cancer into the normal tissue which cannot be seen with the naked eye. Therefore, the incision that is made to remove the tumor is often larger than you might expect. The successful removal of a tumor may be limited by the presence of nearby anatomic structures that have important function and cannot be damaged. In order to perform surgery the patient must be anesthetized. There are certain risks associated with surgery and anesthesia, therefore it is important to test for and discuss other, unrelated, underlying medical problems that may exist so that the safest protocols may be chosen. The tissue that is removed is submitted for histopathologic analysis, so that important information including the type of tumor, a prediction of its biologic behavior, and the “margins” of the surgical resection (how close the tumor extends to the surgical incision, and therefore the likelihood that any microscopic cells were left behind) are known.
Chemotherapy is important in treating systemic or metastatic cancer and works best when disease is microscopic. Alone, it is not very useful for treating solid masses or tumors. Most chemotherapeutic agents work by inhibiting cancer cells which divide and reproduce in an uncontrolled manner. However certain other normal cells in the body are also rapidly dividing, which is why some chemotherapy protocols are associated with side effects involving the bone marrow (and infection-fighting cells) or the gastrointestinal tract, for example.
Chemotherapy treatments may be given orally or by injection. A drug may be administered orally for several days in a row or every other day for several days, followed by a “rest period” with no drugs to be given. Other drugs may be given orally or by injection in one dose, followed by a few weeks without treatment to allow the normal tissue time to recover from the damage inflicted by the drug. The protocol of drugs to be given in regular intervals is called a cycle; your oncologist will specify how the drugs are to be administered and at what days when he or she explains the protocol to you. The number of cycles an animal receives may be somewhat flexible, depending on the tumor’s response to the drugs. It is not uncommon to have to delay a cycle or two during the protocol administration because the patient’s white blood cell count is too low to continue therapy. In most instances, delaying administration of the next drug or drugs for a few extra days does not adversely affect the animal’s prognosis, and it is certainly helpful in preventing serious side effects.
Here is a list of questions you may want to ask your doctor before chemotherapy for your pet begins:
For lymphoma, one of the most common forms of canine cancer, the chemotherapy treatment protocol most often used is the Wisconsin-Madison protocol. The Madison protocol uses the drugs Prednisone, Elspar (L-asparaginase), Vincristine, Cytoxan (cyclophosphamide), and Adriamycin (doxorubicin) during treatments that occur over a period of 26 weeks. Prednisone is taken orally at home, at first in high doses on a daily basis, and will gradually be reduced. The rest of the drugs are given at the clinic, with a different drug being administered during each visit.
You should note that although there is a “standard” for how this and other protocols should be administered, the oncologist can adjust the protocol to meet your dog’s individual needs. If your dog does not tolerate a specific drug well or exhibits more severe side effects, modifications can be made to the drugs used, dosage and schedule of treatment.
Although each dog will vary in their ability to handle chemotherapy, most dogs will exhibit some side effects at one point or another during treatment. Reactions normally do not occur right after treatment though – side effects usually appear 2-3 days after the treatment. Your dog will probably seem a bit more tired than usual, and may not have his or her typical stamina at various points during treatment, but often this is very short-lived. Below is a description of some of the typical side effects of the chemotherapy drugs most commonly used, as described in the Textbook of Veterinary Internal Medicine (2005).
Can cause an allergic reaction. As a result, Diphenhydramine (Benedryl) is usually given to the dog before this drug is administered. Any reaction to this drug would normally occur within 15-20 minutes of administration.
This drug may be the most difficult one for your dog to tolerate, although for many, it is not a problem. Side effects may include:
If your dog does experience severe diarrhea, make sure they continue to drink enough fluids (you may want to put some chicken broth in their water to get them to drink more), and consider giving them a blander, easier-to-digest diet for a couple of days, such as baby food or rice and boiled chicken.
One of the most helpful drugs to keep on hand is Metronidazole (flagyl). This drug can be very helpful if your dog experiences severe diarrhea during treatment (which is not that uncommon), and is given in pill form. A daily dose of Pepcid can also be very helpful in preventing stomach upset, and many pet owners choose to incorporate this into their daily routine. For those who prefer a natural solution, giving your dog a tablespoon or so of canned pumpkin (100% pumpkin, NOT pie filling), can help mild cases of diarrhea.
You should consider investing in an in-the-ear pet thermometer (unless you’re proficient at taking a rectal temperature), as it’s important to monitor your dog for fever throughout treatment. Because chemotherapy drugs often affect the bone marrow and reduce the body’s ability to produce new blood cells, including the white blood cells responsible for fighting infection, it’s very important to identify and treat any infections that might occur as early as possible, as this is potentially the most serious side effect of chemotherapy. A fever is a indication that your dog could have an infection of some kind. Your dog’s white blood cell count will generally be at its lowest 5-7 days after treatment, and this is when they are most susceptible to developing an infection. If your dog develops a temperature, call your vet immediately. This is an emergency!
Two types of weight loss are common in cancer pups — anorexia and cachexia.
Whether the cause is anorexia, cachexia or a combination of both, it’s important to monitor your dog’s weight regularly and to notify your vet if your dog starts to lose weight on a consistent basis.
For lymphoma, it is common to begin seeing results very soon after the first chemotherapy appointment.
Remission does NOT mean that the cancer is gone. It simply means that all clinical signs of the cancer are gone. In the case of lymphoma, your dog has achieved complete remission when the vet can no longer find any enlarged lymph nodes in their body.
Radiation therapy is best utilized for treatment of local microscopic disease in a specific area after a discrete mass is removed with incomplete margins (meaning that tumor cells remain in the surrounding tissue). It is helpful for treating microscopic disease that is left behind because of anatomy limitations, or because the disease was more extensive than could be detected preoperatively. However some tumors can be treated by radiation therapy without surgery, and sometimes “palliative radiation therapy” may be indicated if surgery is not possible. “Palliative radiation” will not cure the disease but it may slow progression or relieve discomfort associated with the cancer. There are many different protocols, which can involve few treatments of a relatively large radiation dose, or many treatments of a much smaller radiation dose. Side effects are possible, but vary according to the protocol recommended, and the area of the body being treated, and should be discussed with your radiation oncologist. It is very important that the patient be positioned exactly the same way when receiving radiation treatments, and that he or she does not move during the treatment, so a very short anesthetic episode is typically necessary for each treatment.
Immunotherapy (sometimes called biologic therapy) is a form of cancer treatment that is still in its infancy in both humans and animals; however, great strides have been made in the last decade. The assumption is made that the growth of some cancers occurs because of a defect in the animal’s immune system. Had the patient’s immunity been normal, the tumor growth should have been suppressed very early, when only a few abnormal cells were present. For this reason, stimulation of the animal’s immune system may be attempted as a part of cancer therapy, through the use of certain drugs and antibody treatments. For some tumors, monoclonal antibodies have been made that bind to tumor-associated antigens (special proteins) on the surface of the cell, sometimes causing the destruction of the tumor cell directly. These antibodies can also be designed to guide a chemotherapy medication or a radioisotope directly to the tumor, targeting its death. Great strides are being made in immunotherapeutic treatment at cancer research institutions for humans, and it is likely that veterinary oncologists will begin to be able to take advantage of some of these developments in the next few years.
The treatment of cancer in animals utilizes many of the same methods available in human medicine. Chemotherapy, radiation therapy, hypothermia, immunotherapy and photodynamic therapy are all part of the arsenal assembled to fight cancer in the pet animal. Most clinical research trials investigating new methods of cancer diagnosis or treatment are conducted at colleges of veterinary medicine. Although considered “experimental”, effectiveness of the treatment has been proven in laboratory animals, safety has been demonstrated in normal dogs or cats, and the therapy is considered to be of potential benefit to the patient. Patients entering a clinical trial must be carefully monitored. Adherence to the treatment protocol is of vital importance to the veterinarian, the pet owner, and to future pets with cancer to ensure that the best in therapy and patient care is available. When a patient treated in a clinical trial dies, a necropsy (autopsy) must be conducted to know the entire effect of the treatment; positive and negative. Many naturally occurring cancers in pet animals closely resemble human cancer and provide meaningful systems for cancer research to benefit both man and animals. The veterinary facility providing the clinical trial, with owner’s permission, may provide specimens obtained from the patient (blood, urine, and/or tumor samples) to basic researchers to gain additional information that may benefit present and future cancer patients. It is important to remember, research is not conducted on the pet itself.