Oral Chemotherapy for Pets is Not a Reliable Substitute for Traditional Chemo

Many owners inquire about oral chemotherapy options in lieu of injectable treatments because they perceive the former as being less “intensive” and therefore less stressful for their pet.

Countless times, owners ask me if I couldn’t just prescribe the “chemo pill” they heard about from one of several typical sources (insert any one of the following: primary veterinarian, friend, cousin, groomer, teenager worker at the pet food store, etc.). I’m the first to admit that it would be remarkable if there was a pan-cancer tablet that effectively treated a multitude of tumors, but oddly enough, in all my years of training as a medical oncologist, I never once learned about the “chemo pill.” Sadly, this magic bullet doesn’t exist.

After a few awkward seconds and a bit of further probing, I’m usually able to discern that owners are asking about one of two oral chemotherapy options: Palladia ®, a tyrosine kinase inhibitor licensed for treating a form of skin cancer called mast cell tumors in dogs, or metronomic chemotherapy, which entails administration of low-dosages of chemotherapy drugs on a continuous basis to inhibit blood vessel growth to malignant cells.

Mainstream use of oral chemotherapy is a relatively recent development in veterinary oncology. For some cancers and the patients attached to those tumors, it can be an excellent treatment alternative. Research with a few specific cancers is available, and data is promising regarding its efficacy. However, evidence based information supporting a superior effect of oral protocols compared to well-studied injectable protocols is lacking for most cancers we treat. In fact, for most tumors, the efficacy of an oral protocol is, at best, theoretical.

Owners are attracted to the option of treating their pet with oral chemotherapy for several reasons. One of the major perceived pros is the incorrect belief that oral chemotherapy is less toxic than injectable treatments. This is a problematic thought process for two reasons: one is it perpetuates the overestimation of frequency and severity of side effects seen with injectable treatment, and the second is it underestimates the potential negative effects of the oral drugs.

Chemotherapy drugs, regardless of form of administration, carry narrow therapeutic indices, and their potential for inducing adverse effects remains a major consequence of their administration.

The typical side effects of injectable chemotherapy include adverse gastrointestinal signs, including vomiting, diarrhea, and/or poor appetite, and a temporary lowering of the recipient’s white blood cell counts. These signs are the same potential consequences of oral medications as well.

Veterinary oncologists typically quote a 20% chance that a pet will display outward signs of illness following chemotherapy. This number holds true whether chemotherapy is given via an injection or via oral form.

Another perceived benefit of oral chemotherapy is that treatment is less stressful for pets because it’s done at home rather than at the hospital, as is done for injections. While I cannot argue against the concept that pets, especially cats, are most comfortable in their familiar environments, the majority of animals remain absolutely calm during in-hospital treatments. The process of administering intravenous chemotherapy is not stressful, and rarely do animals exhibit any distress from the process.

Many owners overestimate the degree to which their pets would be affected by the restraints required for injecting chemotherapy and assume the administration is in some way uncomfortable for the pet. In reality, this simply isn’t true.

A last area of misconception about oral chemotherapy occurs when owners mistakenly believe that animals receiving this form of treatment do not require monitoring. This usually relates to the aforementioned goal of keeping things as low-stress as possible. It also relates to a perception that oral chemotherapy drugs are less costly than injectable drugs because they can be administered out of office. Owners are surprised to learn that pets receiving oral chemotherapy still need to be monitored closely. For example, I recommend monthly exams and lab work for most patients undergoing chemotherapy. Therefore, owners must be aware that choosing an oral treatment plan doesn’t mean their pets are “off the hook” from spending time at the veterinarian’s office.

When you consider how little is known about the potential benefits of oral chemotherapies along with their relative newness, it makes sense that an oncologist would want to monitor your pet even more frequently than for a more well-established therapeutic plan. Cost-wise, all this monitoring means most oral chemotherapy plans are on par with injectable protocols.

What concerns me more than owners wanting to use oral chemotherapy are the primary veterinarians who offer such treatments rather than the standard-of-care injectable protocols because oral chemo requires no specific equipment or training in its administration. The physical act of injecting chemotherapy drugs requires advanced technical skills and experience. Injectable chemotherapy drugs pose health hazard risks to staff members if not properly drawn up in a biosafety cabinet, wearing appropriate personal protective equipment, and using a closed contained system. These fundamentals may not be present in a general veterinary hospital.

If a veterinarian discusses an oral chemotherapy plan, it should not be done under the guise of it being easier, less toxic, or less invasive, especially if that veterinarian lacks the necessary training or equipment to successfully administer injectable drugs. A drug that is “easier” to prescribe is not an appropriate substitute for a proven option for a particular diagnosis.

While I can comprehend why the idea of treating your pet’s cancer with a pill would, on the surface, seem like a simpler and less formidable solution, owners must be aware of the potential limitations and drawbacks of such a treatment plan. Consultation with a veterinary oncologist would be the most effective way to understand the available options and potential risks to your pet’s health.

To locate a qualified veterinary oncologist near you, visit the American College of Veterinary Internal Medicine.