Just like in humans, a cancer treatment plan for our pets takes into account the unique circumstances of the disease and the overall well-being of the pet being treated. Different cancers respond to different treatments.
Some of the most common cancers in dogs include cancer of the liver, colon, skin, lymph nodes, bone, and mammary glands. There are several treatment options to choose from when evaluating how to fight canine cancer.
Before a treatment plan can be made for an individual pet, the cancer must be precisely identified, usually through a biopsy; the extent and possible spread of the cancer must be evaluated (referred to as staging), often through x-rays and lymph node or bone marrow biopsies; and the dog’s general health and ability to tolerate the proposed treatment must be evaluated with a thorough physical exam, blood tests, and sometimes an electrocardiogram (EKG) or ultrasound exam of the heart.
Physical exam: Takes into account weight, a dental check, rectal exam, blood pressure and heart rate.
Blood tests: Includes a complete blood count and blood chemistry panel. A blood count looks at the blood cells themselves and provides information about things such as infection, hydration status, anemia and blood clotting ability. A blood chemistry panel identifies warning signs of liver, kidney and hormonal diseases.
Urinalysis: Your vet will evaluate the color, clarity, and concentration of your pets urine to detect any abnormalities in a number of body systems.
X rays: Are most useful for evaluating the chest, bones, joints and abdomen.
Ultrasound: This test uses high-frequency sound waves to detect problems in the heart, spleen, liver and other soft organs. It’s better at finding tumors, swellings, and fluid accumulation.
CAT scan: Short for computerized axial tomography. A thin beam of x-rays passes through a cross-section of the body in a rotational manner. Using a computer, the scans can be viewed as a three-dimensional image to evaluate subtle changes in tissue.
MRI scan: Short for magnetic resonance imaging. This test uses radio waves and magnetic fields to create images, providing precise views of soft tissues like the liver and brain.
Fluoroscopy: Is the use of x-ray imaging technique using a flouroscope where real-time moving images of organs can be obtained.
Biopsy: Is a sample of tissue from a growth or organ that is examined microscopically.
Fine needle aspiration: Is a simple type of biopsy in which a needle is inserted into a lump or lymph node and a syringe is used to draw a drop of the contents to be examined under a microscope.
Lymph-node biopsy: Is the removal and examination of an entire lymph node to check for metastasis (or spread) of cancer from its original site.
Bone marrow biopsy: Is used to check for leukemia and other cancers of the blood.
Below is an explanation of common cancer treatments, the principles behind them, and their potential side effects.
Cancer that consists of a single tumor or it restricted to a small area of the body can often be removed surgically. The main drawback of surgery as a treatment for cancer is that you can’t be certain it will remove every single cancer cell from the pet’s body, so there’s a possibility that the cancer could recur in the future.
Potential adverse side effects: Bleeding and anesthetic complications during surgery; post-surgical infection; post-surgical pain; possible loss of function of affected areas. Post-surgical pain can be treated safely and effectively and should not be considered a deterrent to surgery. The risk of the other complications is low with most surgeries and can be estimated more precisely for the individual pet.
Chemotherapy uses drugs to kill or damage rapidly dividing cells. It is used to treat blood-cell cancers, such as lymphoma and leukemia, and cancers that have metastasized or are highly aggressive and likely to metastasize. This is a characteristic typical of colon cancer and throat cancer in dogs. These drugs may be given orally or intravenously, or injected directly into the tumor. Cancer cells can develop resistance to individual chemotherapy drugs, so often several different drugs are used in rotation. Chemotherapy usually lasts 6 to 12 weeks. Intravenous chemotherapy drugs are given in the hospital anywhere from once every 3 weeks to twice a week, depending on the drug and the cancer being treated. Oral chemotherapy drugs are given at home once or twice a day.
Potential adverse side effects: Bone-marrow suppression leading to reduced numbers of white blood cells and a risk of infection, nausea, vomiting, or diarrhea; severe chemical burns if chemotherapy drugs leak from the vein into surrounding tissues. (Individual chemotherapy agents may have other, specific side effects which your veterinarian will explain.) Bone Marrow suppression is monitored by running blood tests periodically while a dog is undergoing chemotherapy. If white blood cell levels drop low enough to create a risk of serious infection, chemotherapy is halted for a week or two to allow the bone marrow to catch up in cell production. Antibiotics also can be given to combat infection. Pets undergoing chemotherapy usually don’t develop the severe nausea and vomiting that people sometimes do, but anti-nausea drugs and stomach protectants are given if needed. Dogs rarely lose their hair as a result of chemotherapy.
Radiation kills cancer cells by bombarding them with automatic particles. It is often used to shrink or destroy tumors that are too extensive or inaccessible for surgery, such as cancerous tumors of the mouth and throat (i.e. melanoma), nasal passages, or brain, Radiation treatments are given two to five times a week for three to six weeks. Pets receive a short acting anesthetic before each treatment to ensure that they don’t move once the radiation beam has been precisely aimed at the tumor.
Potential adverse side effects: Burnlike injuries to normal tissues overlaying the tumor; temporary hair loss in the area radiated; mouth pain, drooling, difficulty eating, and loss of appetite when the mouth or throat are radiated. Radiation “burns” are cleaned and protected with a bandage or ointment and usually heal well within a couple of weeks. Mouth pain, drooling, and loss of appetite are treated with mouth rinses and pain relievers; a feeding tube can be placed in the stomach before radiation treatment begins if the pet is likely to have difficulty eating. Mouth irritation usually heals within a couple of weeks after radiation treatment is completed.
Freezing (cryotherapy)or heating (hyperthermia) can sometimes be used to kill small (less than 1/3 inch in diameter) benign or malignant tumors on the surface of the body. Potential advantages of cryotherapy and hyperthermia over surgery are that they are fast and require only local anesthesia. The main drawback is they will not kill cancer cells that have spread beyond the small area frozen or heated. Chemotherapy or radiation is sometimes used afterward to kill stray cancer cells.
Potential adverse side effects: Cryotherapy and hyperthermia leave a wound about double the size of the original tumor that scabs and heals’ with normal wound care (cleaning and ointment or bandage), within about two weeks. The hair in that area may grow back a different color or texture than it was originally.
A pet’s own white blood cells will attack and kill cancer cells if they find them and recognize them as a threat. Immune-system motors are substances given orally or by injection that rev up the immune system and help it to recognize and target cancer cells. The main drawback is that a dog’s immune system is unlikely to be able to kill every tumor cell in a cancer that has already gotten a head start. Therefore, immune-system modulators are most often combined with other cancer treatments such as surgery, chemotherapy, or radiation.
Potential adverse side effects: These vary with the specific modulator. Some have no adverse side effects.
To learn more about cancer treatment in companion animals, please download a presentation from Dr. Nancy Gustafson, Radiation Oncologist.