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Focused Microwave Phased Array Thermotherapy for Ablation of Early-Stage Breast Cancer: Results of Thermal Dose Escalation

From Harbor-UCLA Medical Center (HIV, KDG, RV), Torrance, California; The University of Oklahoma (WCD), Health Sciences Center, Oklahoma City, Oklahoma; Columbia Hospital (RAG), West Palm Beach, Florida; Martin-Luther University (SHH-K), Halle, Germany; and Massachusetts Institute of Technology (AJF), Lexington, Massachusetts.

Correspondence: Address correspondence and reprint requests to: Hernan I. Vargas, MD, Division of Surgical Oncology, Harbor-UCLA Medical Center, 1000 W. Carson Street, Torrance, CA 90509; Fax: 310-782-1562; E-mail: hvargas{at}ucla.edu

Background: Tumor ablation as a means of treating breast cancer is being investigated. Microwave energy is promising because it can preferentially heat high-water-content breast carcinomas, compared to adipose and glandular tissues.

Methods: This is a prospective, multicenter, nonrandomized dose-escalation study of microwave treatment. Thermal dose was measured as (1) thermal equivalent minutes (cumulative equivalent minutes; CEM) of treatment relative to a temperature of 43°C and (2) peak tumor temperature. Microwaves were guided by an antenna-temperature sensor placed percutaneously into the tumor. Outcomes measured were pathologic response (tumor necrosis) side effects.

Results: Twenty-five patients (mean age, 57 years) were enrolled. The mean tumor diameter was 1.8 cm. Tumoricidal temperatures (>43°C) were reached in 23 patients (92%). Tumor size was unchanged after thermotherapy (P = not significant). Pathologic necrosis was achieved in 17 (68%) patients. Complete necrosis of the invasive component was achieved in two patients. One hundred forty CEM is predictive of a 50% tumor response, and 210 CEM is predictive of a 100% tumor response (P = .003). Univariate linear regression predicts that peak tumor temperatures of 47.4°C and 49.7°C cause a 50% tumor response and a 100% tumor response, respectively.

Conclusions: Thermotherapy causes tumor necrosis and can be performed safely with minimal morbidity. The degree of tumor necrosis is a function of the thermal dose. Future studies will evaluate the impact of high doses of thermotherapy on margin status and complete tumor ablation.

Key Words: Breast cancer • Ablation • Minimally invasive • Microwave • Cancer treatment