Gloria Hwang, MD, likes to cook tumors. As an interventional radiologist at Stanford, she uses a variety of ablation techniques to remove small tumors from her patients – radio frequency ablation, cryoablation and microwave ablation. But recent advances in microwave systems have improved Hwang's ability to destroy larger tumors, up to four centimeters in size, and tumors embedded in blood rich organs like the liver. And for patients like Gwen McCane, this innovation came at a perfect time.
Three years ago, McCane sought medical attention for what she thought was acid reflux. Instead, she faced a pancreatic cancer diagnosis. Chemotherapy and radiation beat back the disease, but then it appeared in her liver. At first, she couldn't find a physician who would treat her because her new tumors were small and deep inside her liver. She was told there was nothing that could be done. Her persistence led her to Stanford, and to Hwang, who felt that McCane's tumors could be reached and destroyed using microwave ablation.
"Microwave ablation offers an option for a significant number of people who may feel like they've run out of options," says Hwang. "That's a lot of what we do in interventional radiology—treat the sickest patients who can't tolerate toxic medications or major surgery."
Larger zone of kill
Both microwave ablation (MA) and radio frequency ablation (RFA) kill tumor cells by heating up the tissue around needles placed through the skin. But RFA heats tissue relatively slowly, so nearby blood vessels can have a cooling effect on the ablation zone. "That is one of the most common reasons for treatment failure with radio frequency ablation," explains Paul Laeseke, MD, PhD, a radiology resident at Stanford, and clinical affairs director at NeuWave Medical, the developer of the microwave ablation system used at Stanford.
"With microwave ablation, you can heat tumors up very quickly, using higher heats than RFA, and you can do so near blood vessels because you can stop the cooling effect of the blood vessels," says Hwang. Microwave ablation also allows interventional radiologists to use multiple probes at the same time, and delivers a spherical ablation zone. "All of this together means you can get larger zones of kill and treat bigger tumors with microwave ablation," she says.
There's also a fundamental difference in how microwaves heat the tissue, Hwang says. Rather than passing an electrical current through the patient's body, as does radio frequency ablation, microwaves heat the tissue by oscillating nearby water molecules. Microwaves do not require patient's to wear grounding pads, and microwave energy can pass through air, which allows it to treat tumors in organs such as the lung.
"The ability to treat tumors in the lung is one of the biggest reasons physicians have become interested in microwaves," says Laeseke. "Lung cancer is so common. And many people with lung cancer have a number of co-morbidities, so they're not very good candidates for surgery." Microwave ablation gives this population of patients a new opportunity to become tumor free.
Both Hwang and Laeseke believe microwave ablation will become a more accepted treatment for a number of tumors, not just those that are inoperable. The minimally invasive procedure doesn't require a lengthy hospital stay, it quickly treats tumors that are otherwise difficult to eradicate and it does so with minimal damage to healthy tissue.
When to consider microwave ablation
Microwave ablation is most commonly used in the liver, lungs, kidneys and bone. According to Hwang, patients should be referred to an interventional radiologist if they have liver-dominant metastatic disease with good control of the primary site; masses ideally four centimeters or smaller in size; three or fewer masses; and patients with peripheral lung tumors (primary or metastatic) who are not good candidates for surgery.
"Before this technology, most people would say if a patient is healthy enough for surgery, then that's the way to go because then you know you've taken the tumor out of the body," says Hwang. "It's hard to argue with that." But many patients, like McCane, can't tolerate surgery or have tumors that can't be reached by surgery. Microwave technology gives them a new option.
By Grace Hammerstrom