Multiple strategies take aim at removing breast lesions

April 1, 2004

According to research presented at the 2003 RSNA meeting, interventionalists are having good luck ablating anything that will sit still. Five-year data on radio-frequency ablation of liver masses is promising enough that proponents suggest it may become an alternative to surgery. Studies in the lung and kidney show progressively better outcomes. And ablation probes have been successfully applied to bone metastases as a palliative measure.

According to research presented at the 2003 RSNA meeting, interventionalists are having good luck ablating anything that will sit still. Five-year data on radio-frequency ablation of liver masses is promising enough that proponents suggest it may become an alternative to surgery. Studies in the lung and kidney show progressively better outcomes. And ablation probes have been successfully applied to bone metastases as a palliative measure.

In the breast, however, it's a different story. Investigators say work on breast tumors is at least five years behind achievements in the liver, and it will be years before ablation could become an alternative to lumpectomy, if ever.

A number of institutions are trying out RFA, cryoablation, laser thermal therapy, and focused ultrasound, usually with ultrasound guidance but occasionally with MR. Most research has been led by surgeons, who typically remove the treated area several days after ablation.

"Surgery works well, and it is definitive," said radiologist Dr. John McGahan, who presented work at the RSNA meeting that he coauthored with colleagues in the surgery department at the University of California, Davis. "But in breast cancer, you want to find something that is both cosmetically appealing and definitive. Lumpectomy is a great procedure, but it's deforming."

McGahan and colleagues are using ultrasound to guide RF probes, one of the most common and straightforward approaches. Their initial study involved seven patients with ultrasound-visualized tumors smaller than 1.5 cm. The hypoechoic masses were treated with the ablation probe until they became echogenic and indistinguishable from the surrounding tissue on ultrasound. The procedures were performed in a surgical suite, and the tumors were removed afterward.

The trial at Davis is ongoing, but a similar study at the Vancouver Island Health Authority in Victoria, BC, saw complete coagulative necrosis in 19 to 22 patients. A small study at Ohio State University found no residual lesion enhancement on post-RFA MR imaging for eight of nine patients, but the excised tumors varied from completely coagulated to retaining some recognizable malignant cells.

Ultrasound and RF may be the most convenient tools for breast ablation, but they have limitations, McGahan said. If a lesion lies too close to the surface, RF may burn the overlying skin; too close to the chest wall, and it could burn the pectoralis muscle. To minimize the risk, he and surgeon Dr. Vijay Khatri place ice packs on some patients

during the procedure. Ultrasound tends to become hard to read during RF as bubbles from the heated tissue obscure image quality.

Investigators at the University of Michigan are studying cryoablation. Seven of nine patients showed complete necrosis after undergoing cryotherapy of lesions 8 to 20 mm in diameter. A team of researchers led by surgeon Dr. Michael Sabel and radiologist Dr. Marilyn Roubidoux surrounded the tumors with an additional 5 to 10-mm margin of ice ball. One patient had extensive ductal carcinoma in situ beyond the iceball margin, while another had a large tumor with an additional focus area beyond the iced region.

"Right now we think we can do about 1.5-cm diameter with either RF or cryo, but no larger," Sabel said.

Cryoablation doesn't carry the burning risks for the chest wall or skin, and preliminary work with fibroadenomas suggests that the tissue destroyed by the ice ball may be reabsorbed by the body over time. RF-treated areas may shrink a little but remain as hardened lumps in the breast.

Sabel is hoping to find evidence that the proteins left behind in the iced tumors may stimulate the body's immune response and prompt it to go after other cancer cells.

Other researchers around the world have worked with MR-guided laser-induced thermotherapy and MR-guided focused ultrasound, both of which are completely noninvasive. MR has the potential to identify lesions missed on ultrasound or mammography, but the expense and the challenges it adds to interventional procedures are just two of many factors to be worked out in the fledgling field.

The most pressing questions for now are whether one or more of the ablation techniques can achieve complete necrosis and how to determine which patients are the best candidates, Sabel said. Lobular carcinomas may be too big in many cases, DCIS may extend beyond the invasive tumor, and lesions that are hard to identify on ultrasound or dense mammograms are problematic as well. Until investigators can be confident that ablation is completely destroying all tumor tissue, biopsy, excision, and other invasive measures will follow.

On that basis, Sabel said, this interventional technique may not end up in the hands of radiologists in the way that ablation of hepatic or renal masses has.

"I think this will remain with surgeons because it will need to be done with sentinel node biopsies for axillary staging," he said. "It is important for surgeons to be on top of technology advances so as not to lose ground to other specialties."