Radiation therapy is given in several small doses, called fractions, over a period of 3 to 4 weeks. These small daily fractions are given to maximize the damage to cancer cells and limit the damage of normal cells. Fortunately, the damage to normal cells occurs only in the parts of the body that are exposed to the radiation. Chemotherapy Chemotherapy is used in both humans and animals when the spread of a cancer has gone beyond a local region or if the cancer exists in multiple locations. There are many different classes of chemotherapy agents, and each class has its own distinct mechanism of action and toxicity.
Cancers can become resistant to chemotherapeutic agents.
For this reason it is important to use a number of different drugs in chemotherapy protocols, each at the highest dose that is tolerated by the patient. The goal of chemotherapy is to give enough drug to kill all the cancer cells while limiting damage to normal cells. Side effects of chemotherapy occur when normal cells are damaged by the treatments. The most common side effects associated with this chemotherapy in animals are vomiting, diarrhea, and a decrease in appetite. Most veterinary chemotherapy protocols are well tolerated.