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.

Below is an explanation of common cancer treatments, the principles behind them, and their potential side effects.

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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; postsurgical infection; postsurgical pain; possible loss of function of affected areas. Postsurgical 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.

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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. 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.

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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 tumors of the mouth and throat, 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: Burn like 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.

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Cryotherapy and hyperthermia

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.

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Immune-system modulators

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.

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