Cancer researchers constantly strive to expand the arsenal of weapons to treat the disease, particularly for people with tumors that aren’t responsive to conventional treatments. One such option is a minimally invasive approach called thermal ablation, which involves placing a needle into a tumor and applying extreme heat or cold, which kills the cancer while preserving healthy tissue. In addition to destroying tumors, thermal ablation may actually activate immune cells to attack the cancer.
Memorial Sloan Kettering now has one of the biggest ablation programs in the United States, says Stephen Solomon, Chief of the Interventional Radiology Service and Director of the Center for Image-Guided Interventions. “We’re treating approximately 300 people a year, frequently on an outpatient basis that allows patients to go home after the procedure the same day.”
However, thermal ablation cannot be used in some patients.
“Thermal ablation can cause scarring in healthy tissue near the tumor, making it inappropriate for use on some tumors near blood vessels, nerves, bile ducts, and other sensitive structures,” says Mikhail Silk, a medical student at SUNY Downstate College of Medicine, in Brooklyn, who is conducting research in collaboration with the Interventional Radiology Service. “It also can fail to kill every cancer cell if the tumor abuts a major blood vessel because blood flow dissipates some of the extreme heat or cold emitted from the needle — a phenomenon called the heat sink effect.”
Punching Holes in Cells
Now a new, minimally invasive treatment that uses an electric current to punch tiny holes in cancer cell membranes is showing promise against challenging tumors. Called irreversible electroporation (IRE), the technique uses tiny needles to give cancer cells a jolt of electricity.
The electricity produces holes in the cell membranes, which disrupts the balance of molecules inside and outside the cells. IRE causes no scarring or inflammation in nearby healthy tissues, and there is no heat sink effect.
“Blood vessels and nerves are made not just of cells but also have protein structures surrounding them,” Dr. Solomon explains. “Because proteins don’t have electric membrane potential, these structures are largely protected from IRE, making it possible to destroy a tumor safely without destroying the structural integrity of an organ.”
IRE holds particular potential for treating liver, lung, and pancreatic cancers that are close to blood vessels and other sensitive structures — situations in which normal heat or cold ablation is not feasible.
Encouraging Study Results
After validating the safety of IRE in animal studies, Memorial Sloan Kettering’s interventional radiologists and surgeons have begun using the procedure in select patients who are not eligible for other treatments — particularly, patients with cancer that has spread to the liver from other sites in the body.
Early results suggest IRE can be effective and safe. In the January 2014 issue of the Journal of Vascular Interventional Radiology, Dr. Solomon’s team reports that IRE was used successfully in 11 patients to treat a total of 22 small tumors that had spread to the liver from other locations. In 15 treatment sessions, the tumors — which had a median size of 3 centimeters — were destroyed with no major complications. Many of the tumors were located less than 1 centimeter from bile ducts, making thermal ablation too risky.
Memorial Sloan Kettering specialists will continue to explore IRE in other types of cancer, although in every case it needs to be compared with thermal ablation and other minimally invasive treatments. Dr. Solomon’s team recently received a grant from the National Institutes of Health to investigate the use of IRE in lung cancer, which they hope to begin in 2014.
A strong feature of the Interventional Radiology Service has been the addition of a biomedical engineer, Govind Srimathveeravalli, who has worked with the clinical team to optimize the use of IRE.
“For complete tumor destruction with IRE, it is important to achieve a uniform electric field within the target region,” Dr. Srimathveeravalli says. “As tumors are heterogeneous in nature, treatment planning for IRE can be a challenge to physicians. I use physics simulations and work with Dr. Solomon to develop guidelines for optimizing treatment plans. We also perform research to develop new devices that will extend the reach of IRE therapy to new anatomical locations.”
“Our research program will be focusing a lot of energy on developing and refining IRE over the next few years,” Dr. Solomon adds. “There are still important questions that need to be answered — such as whether IRE actually destroys all the cancer cells — but we hope it becomes another tool that physicians can rely on when nothing else is suitable.”