According to the National Cancer Institute, more than one out of every 20 living Americans has survived cancer. Chemotherapy, sometimes along with radiation or surgery, has saved them. But what about pets who get cancer? There, too, chemotherapy for pets can be a useful tool, usually with the same medications in smaller doses – but with a different goal from human treatment.

Human doctors treat cancers aggressively because patients who survive may live many more years and can understand the reasons for the pain and weakness they endure. You can’t explain to an animal why it’s suffering, and an older pet may live only another couple of years if treatment succeeds. So, CARE’s doctors have a different focus: They want to kill the cancer but make sure animals have excellent quality of life while undergoing treatment.

What Is Chemotherapy?

It consists of medication (or a combination of medicines) given orally or intravenously to target cancer cells. In some cases, a doctor can give an intralesional injection directly into a scar. An intracavitary injection might also be used.

Vets apply standard dosing protocols, based on weight and possibly affected by other health conditions. Most of these drugs come from human chemotherapy treatments; a few have been specified only for veterinary use. Certain human drugs may be too toxic for animals, even at lower doses, or unable to be absorbed usefully by animals.

Depending on the size and nature of a tumor, chemotherapy for pets can be done in tandem with radiation and/or surgery. Lymphoma, multiple myeloma and histiocytic sarcoma may respond well to chemotherapy. Tumors of the head and neck, non-operable bone tumors, brain tumors and heart tumors may require chemo and radiation. Surgery and chemo may be indicated for osteosarcoma, lung tumors or hemangiosarcoma.

How Do We Know Chemotherapy for Pets Is Needed?

Except for leukemia and a few rarer diseases, bloodwork won’t reveal the presence of cancer. Owners will typically notice a lump or swelling somewhere on the body, and vets will test for cancer by doing a fine needle aspiration or a biopsy and studying the diseased cells.

Doing an aspiration tries to hit the area where the cancer seems to be concentrated, whereas doing a biopsy during surgery takes a whole piece of the tumor. Neither can be 100 percent accurate, but they’re likely to give good results.

Diagnosing a cancer that is not externally obvious can be difficult. A pet owner might choose blood work and imaging – chest and abdominal X-rays or ultrasounds – as often as every three months for an older animal. (Oncologists recommend doing these every six months as a minimum safeguard in middle aged to older patients.) Yet some cancers progress so fast that the onset to death lasts only a few weeks, allowing no time for treatment.

How Do Pets Respond to Chemotherapy?

Animals usually tolerate chemotherapy better than humans, partly because the doses are lower and the protocols are less intense. Perhaps one pet in five will experience one of the three common kinds of side effects.

The first relates to the gastrointestinal tract, from decreased appetite or nausea to vomiting or diarrhea. The second and rarer problem is bone marrow suppression, which doesn’t show symptoms. The third is alopecia, but that’s uncommon: Animal fur grows differently from human hair, so they seldom lose it during chemotherapy.

CARE follows up after the first treatment to make sure pets tolerated the treatment. (Pets who tolerate it early generally handle it well long-term.) Doctors treat side effects immediately, lowering drug doses or eliminating them if they’re taking too much of a toll on the animal. When pets can’t have chemotherapy, palliative care lets them live with a minimum of pain.

Sometimes animals remain on maintenance doses to keep cancer at bay. CARE recommends that owners monitor the disease with bloodwork and imaging. Whatever happens, the goal will always be the same: the highest standard of quality of life for the pet.

Charlotte Animal Referral and Emergency treats pets like a medical center for humans treats people. CARE operates 24 hours a day, 365 days a year. It provides all types of treatment, from emergency attention to board-certified specialty work, once you get a referral from a primary care veterinarian. You can take a visual tour of the practice at

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