Metronomic Chemotherapy

Blake Marcum, MS, DVM, Residency-Trained in Oncology

The word chemotherapy can stir up a lot of emotions when people hear it. Chemotherapy carries a negative connotation for many people who have had experience with cancer care in humans. When the term comes up in reference to pets, owners are often left with many questions about treatment options and whether those treatments are going to be worse than the disease itself. Typical chemotherapeutic agents are given as a maximally tolerated dose. This means that the goal is to treat at a dose that is high enough to kill cancer cells, but low enough to minimize undue side effects for the patients.

In dogs and cats, that threshold for acceptable toxicity is much lower than it is in human patients, so our patients are treated at lower doses so they tend to tolerate chemotherapy very well. Despite this, typical chemotherapy may not be the best option for every patient or client. Some cancers may not have a clear “best” choice. Some owners may be looking for an option that helps with disease but offers the lowest possibility of side effects. Other owners may be looking for an option that minimizes trips to the oncologist due to time constraints, stress for the pet, or financial limitations. In these situations, we may offer an alternative option for treatment called metronomic chemotherapy.

Metronomic chemotherapy is the use of low-dose, regular (daily to every other day) oral chemotherapy. This is a treatment that has a very low chance of acute side effects; and it is given at home, rather thanat the oncologist’s office, so visits are minimized. Typical chemotherapy treatment involves high doses of chemotherapy to try to kill the cancer cells without killing too many of the patient’s normal cells. Standard treatment targets the actively dividing tumor cells, but it is also harmful to the actively dividing normal cells such as those in the bone marrow, gastrointestinal tract, or hair follicles.

With metronomic chemotherapy, our goal is to attack the vascular cells that create new blood vessels for tumor cells to grow. By preventing blood supply, we can effectively slow the process of tumor growth or metastasis (tumor spread). Metronomic chemotherapy may also alter the immune system to help it better identify the cancer cells.

Metronomic chemotherapy has been shown to be an effective treatment for slowing the progression of a variety of tumors including soft tissue sarcomas, mast cell tumors, hemangiosarcoma, and transitional cell carcinomas.  In general, the treatment helps to slow the disease or prevent further growth of tumors, but it does not typically result in tumors shrinking. It can also be used to help slow or decrease the risk of metastasis. For many pets, whose tumors are not having a negative effect on quality of life, this can be a very reasonable, low-risk treatment option. If owners are unsure about treatment options for their pet’s cancer, it is important that they know that there are plenty of choices, and metronomic chemotherapy may be a good option for their pet.

Dr. Blake Marcum is part of our Oncology team at Veterinary Specialty Center.


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