SAN ANTONIO — Magnetic resonance-guided focused ultrasound shows great potential as a totally noninvasive means of ablating breast cancer, Dr. Yukiko Yasuda reported at a breast cancer symposium sponsored by the Cancer Therapy and Research Center.
Indeed, results of a published phase II 30-patient trial conducted by Dr. Yasuda and her coinvestigators were so favorable that a phase III Japanese trial is ongoing (J. Am. Coll. Surg. 2006;203:54–63). In addition, a 600-patient multinational study to include the Mayo Clinic, Rochester, Minn.; Johns Hopkins University, Baltimore; and Brigham and Women's Hospital, Boston, is on tap, according to Dr. Yasuda of Breastopia Namba Hospital, Miyazaki, Japan.
MR-guided focused high-intensity ultrasound (MRgFUS) is a logical extension of the trend toward using breast-conserving therapy to lessen impact on quality of life.
The treatment achieves thermal tumor ablation by concentration of ultrasound pressure waves inside the breast without physical penetration. When applied properly, there is no clinically significant heating of skin or other tissues along the ultrasound beam's path. Using real-time, closed-loop contrast MR feedback to monitor temperature changes at the target site, the operator can deliver destructive energy to a given point within 1 mm of accuracy.
In theory, this approach should result in less anesthesia, fewer infections, and faster recovery than with conventional surgical excision—and with no scars. Those are the potential pluses. The procedure's disadvantages are the expense of the technology and the lengthy treatment session. In the phase II study, a single 2-minute sonication destroyed 0.16–0.67 mL of tissue. Complete tumor ablation required an average treatment time of 2 hours, 20 minutes.
However, this is a young technology, and two major technical advances to be introduced in the near future will speed treatment time and accuracy. One is a boost in the number of focused ultrasound transducer elements from the current 208 to 2,000. The other is upfield high-spatial-resolution MRI. These developments will permit three-dimensional treatment planning and therapy, she said.
Dr. Yasuda reported on 22 Japanese breast cancer patients who underwent MRgFUS outside of a clinical trial. No adjuvant radiotherapy was used. The patients were subsequently followed with contrast-enhanced MRI and diagnostic ultrasound every 3 months for a median of 15 months.
During that time, one patient developed a local recurrence of pure mucinous carcinoma. Playback of stored treatment records revealed the explanation: insufficient temperature rise in the treated primary tumor, probably because of the dampening properties of the mucus. Armed with this information, operators can induce a higher temperature spike in patients with this subtype of carcinoma and avoid repeating the problem.
Treatment was performed using InSightec's ExAblate 2000 ultrasound system integrated into a 1.5-Tesla GE Healthcare MRI scanner. The ExAblate 2000 is Food and Drug Administration-approved for treatment of uterine fibroids.
In MR-guided focused ultrasound, a beam of focused ultrasound energy emanates from the transducer through the skin and breast to a focal point on the tumor. InSightec Ltd.