Metronomic chemotherapy.

Chemotherapy drugs are usually administered at doses that are high enough to result in an obligatory break period to allow for the observation of potential side effects and institution of supportive care, if required. In recent years, efforts to administer chemotherapy on a more continuous basis, with a much shorter break period, or none at all, have received increased interest, and the practice has come to be known as metronomic chemotherapy. The basis for success with this currently investigational approach may be rooted in continuous drug exposure to susceptible cancer cells, inhibition of tumor blood vessel growth-a process known as tumor angiogenesis, and/or alterations in tumor immunology. Increased benefit also appears to occur when metronomic chemotherapy is used in combination with newer, targeted antiangiogenic agents, and therefore represents a promising approach to combination therapy, particularly as targeted oncology drugs make their way into veterinary oncology applications. There is still much to be learned in this field, especially with regard to optimization of the proper drugs, dose, schedule, and tumor applications. However, the low cost, ease of administration, and acceptable toxicity profiles potentially associated with this therapeutic strategy make metronomic chemotherapy protocols attractive and suitable to veterinary applications. Preliminary clinical trial results have now been reported in both human and veterinary medicine, including adjuvant treatment of canine splenic hemangiosarcoma and incompletely resected soft tissue sarcoma, and, further, more powerful studies are currently ongoing.