Should a Pet With Cancer Get Chemotherapy?

by Michael Fagan, DVM

“Cancer” is a word that can induce fear and other emotions.  Many people have personal experiences with cancer and chemotherapy that they don’t wish to impose on their pets.  To be sure, cancer and the many treatment options we can offer are not to be taken lightly.  However, we do have many patients that have received treatments for cancer with favorable outcomes, from cures or long term remission to improved quality of life for many months to years.

The most important factor in determining treatment options and recommendations is what type of cancer the pet has developed.  “Cancer” is a very broad term, with many different types and variable response to different kinds of treatment.  Each patient with cancer is unique.  We offer options based on the type of cancer, symptoms or lack thereof, the pet’s overall health, and owner preferences.  Some cancers are best treated by surgical removal.  Others respond best with radiation, chemotherapy, or immunotherapy.  Some have a poor prognosis regardless of treatment, and control of pain or other symptoms takes priority before opting for euthanasia. We will often consult with a veterinary oncologist as we explore the options available.

The goals of treatment are also unique to each patient, but as a general rule, we aim for a cure only if we can preserve good quality of life throughout the process.  More often, we are trying for a long term remission or control of tumor growth for many months to a few years.  The most common treatment for cancers that are not curable with surgery is chemotherapy of one form or another.

Herein lies a vital difference between veterinary and human medicine:  in human medicine, the treatment goal is often to eliminate the cancer and then recover the patient; in veterinary medicine, we want to preserve good quality of life while limiting the cancer.  In other words, we use drugs, doses, and treatment schedules that minimize side effects while still providing the benefit of remission or delayed growth of the cancer cells. 

With chemotherapy, we have had lymphoma patients live longer than two years; bladder cancer patients, one to two years; dogs with nasal tumors, over a year; most with minimal side effects from the chemotherapy and reduction or elimination of symptoms caused by their cancer.  Unfortunately, not all patients respond, and not all tolerate the chemotherapy equally.  Each patient needs to have its treatment protocol customized. 

One relatively new approach to chemotherapy is using small daily doses instead of higher intermittent doses.  This tends to reduce toxicity and has a different effect on tumor growth.  Rather than actively killing tumor cells directly, low-dose daily therapy (called metronomic therapy) may work by reducing the blood supply to the tumor and by allowing the immune system to respond more aggressively. 

The bottom line is that we have many options for treating the many kinds of cancer that we diagnose in pets, including surgery, radiation (by referral to a veterinary oncologist), traditional or metronomic chemotherapy, immunotherapy (there is a vaccine for melanoma!), and/or palliative care (control of pain and other symptoms caused by the cancer). In animals we also have the option of euthanasia when appropriate but that is a subject for another blog.