Just Ask the Expert: Intralesional chemotherapy
Q: When do you use intralesional chemotherapy? In what cases might it be useful?
A: Effective cancer treatment in dogs and cats necessitates the delivery of chemotherapeutic agents at concentrations high enough to cause cancer cell death. As such, the pharmacokinetics and biodistribution of chemotherapeutic agents are crucial factors in treatment outcomes. It has been documented in certain solid tumors that the pressure within the interstitial space (space found between tumor cells) is very high. Elevated intratumoral interstitial pressures would impede the diffusion of systemically administered chemotherapy from the bloodstream into the tumor interstitium. Subsequently, tumor cells would not be exposed to high concentrations of anticancer agents.
The intralesional delivery of chemotherapy is attractive in the sense that one can instill a high concentration of drug into a small confined area. Intralesional delivery thereby maximizes tumor cell exposure to cytotoxic drugs and, it is hoped, enhances anticancer effects. Although intralesional therapy does provide a pharmacokinetic advantage, it also can result in some undesirable effects including 1) drug exposure to the environment and to people as the compound oozes out of the injection site and 2) potential local tissue necrosis secondary to nonspecific direct cytotoxic effects to normal local tissues.
In light of these drawbacks, intralesional chemotherapy is not particularly attractive for most veterinarians. However, some specific instances do exist in which intralesional therapy is effective. One such example would be the injection of corticosteroids (triamcinolone) directly into a cutaneous mast cell tumor. This form of intralesional therapy is well-tolerated and effective in reducing mast cell tumor size, and accidental human exposure to the corticosteroids used would not be a serious problem.
Timothy M. Fan, DVM, PhD, DACVIM (internal medicine and oncology)