There is a Yiddish proverb that translates to “Sometimes the remedy is worse than the disease.” I often think of this adage when discussing chemotherapy with owners who are fearful of potential side effects in their pets.
The biggest concern owners have when considering chemotherapy is, “Will it make my pet sick?” An owner’s personal experience with cancer treatment, or that of a friend or family member, or even those garnered from the media, will color their perception of what they feel their pet will go through. It can sometimes be a struggle for me to convince them otherwise.
The chemotherapy drugs we use in veterinary oncology are the same ones used to treat cancer in people. There are no differences between the doxorubicin, carboplatin, or CCNU I use in my patients, when compared to what is administered to humans.
When I prescribe such medications for my veterinary patients, I am actually using the drugs in what is known as an “off label” designation. This means they are used in a different way from what they are licensed for. For me, this typically means I am administering them to a different species from the one they were initially developed to treat. In fact, the only truly veterinary approved chemotherapy drugs available in my arsenal include Palladia® and Kinavet®, which are oral medications licensed to treat cutaneous mast cell tumors in dogs.
All chemotherapy drugs have what is known as their “maximally tolerated dose” (MTD). The MTD of any drug (chemotherapetutic or not) is determined through clinical trials in live animals. During these trials, investigators are looking to see what dose can be safely administered to pets, with a previously determined acceptable rate of side effect. It would be ideal to develop a drug with 100% efficacy and 0% side effect, but in reality, this is not practical.
Typically, trials designed to determine the MTD of a chemotherapy drug are designed to enroll a specific number of patients at an initial starting dose and then record any adverse side effects that occur. If no side effects are noted, the dose can be increased slightly and more pets can be enrolled into the study, and again side effects are recorded. This pattern is continued until roughly 25 percent of pets experience what are considered mild side effects. Once this point is reached, this is considered the MTD for the drug in question. This should equate to the prescribed dose for any future patient.
The criteria for assessing severity of side effects during a trial is based on an objective scale that literally records the number of vomiting episodes, number of stools per day, and percent decrease in appetite. The same measures are also made regarding bloodwork parameters (e.g., white blood cell counts, platelet counts, liver values, etc.). If lab tests were to show that an animal developed a low white blood cell count, or elevations in organ function tests, this too would be an indication of a MTD for the drug in question.
Establishing a MTD allows me to tell an owner “Your pet has less than a 25 percent chance of a severe or moderate reaction to this drug.” This also translates to meaning their pet has more than a 75 percent chance of not experiencing any adverse signs whatsoever.
In reality, I understand none of this scientific information can comfort an anxious owner when it comes down to making a decision about their pet. Even as I describe the potential risks and statistics surrounding the exceedingly low chance for a poor reaction from treatment to the average pet owner, I know they are not consoled by the data. Ultimately, none of it will matter if it’s their “child” who develops signs. And even the mild signs may be too impacting for them to handle.
This is what makes it particularly tough for me to answer when people ask me “What would you do if this were your pet?” Since I am a veterinary oncologist and I work in a veterinary hospital, I know exactly what signs to look for, I have rapid access to treatments for even minor signs, and I can bring my pets to work with me and watch them the entire time. Since I am a veterinary oncologist and I owned a pet with cancer, I can empathize with how terrible and awful it feels to watch your pet feel sick from a deadly disease (note my own pet was not sick from chemotherapy but rather because his cancer was too advanced for treatment at the time of diagnosis).
Whatever a person’s experience with chemotherapy, I urge them to try to understand that the goal of veterinary oncology is very different from human oncology. As one of my mentors would always say, “It’s not life at all costs, it’s quality of life for as long as possible.” The remedy can certainly be worse than the disease, but fortunately, in veterinary oncology, this occurs far less frequently than pre-conceived notions may suggest.
So the take home message in the Yiddish proverb is full of applicable wisdom, but it’s also important to keep a good perspective on scientific facts … except when considering my all-time favorite proverb:
“The husband is the boss — if his wife allows.”
Happy one-year anniversary to my wonderful husband! Here’s to many more years together filled with love, laughter, and patients who keep us up at night!
Dr. Joanne Intile