Differences in Dielectric Properties between Malignant and Normal Breast Tissue: Preliminary Results of the MicroBlate® Study.

Abstract

Abstract Background: Minimally-invasive microwave ablation techniques for the management of breast diseases are an emerging technology. These techniques rely, to a certain extent, on the difference in dielectric properties of normal and malignant human tissue. In our unit, we are currently studying the efficacy of a new microwave based technology, MicroBlate®, which has the unique feature of being able to measure tissue impedance and deliver microwave frequency impulse to tissues based on this impedance feedback. In this study we have compared the dielectric properties of normal and malignant breast tissues using this probe to establish proof of principle.Methodology:Impedance of freshly excised mastectomy and reduction specimens were measured ex-vivo using the MicroBlate® probe. This probe was attached to the end of the precision open-ended co-axial cable connected to an Agilent 4-port PNA-L Microwave network analyser (10MHz – 20 GHz). Impedance (Z) was intially recorded as two values which are vector quantities: real (R), which reflects the tissue resistance, and imaginary (X), a measure of tissue reactance. The overall impedance was then calculated using the standard mathematical formula, Z= √(R2+X2). Measurements were performed on adipose, glandular and malignant breast tissue immediately following surgical excision. Differences in the impedance values between these tissue types were calculated and the results analysed using appropriate statistical tests.Results:Our study shows a measurable difference in the dielectric properties of malignant and normal breast tissue. Our data supports the technological basis of MicroBlate®, a minimally invasive microwave ablation technology with impedance feedback, further ex-vivo studies are needed to determine its efficacy in ablating benign and malignant breast tissue. 28 patients undergoing elective mastectomy (n=26) and reduction (n=2) were included in this study between Feb – May 2009. Of the 26 patients undergoing mastectomy, 19 had invasive malignancy and the remaining 7 had in-situ malignancy only. The median age of the patients was 58 years (range 22-80 years). The average impedance of adipose tissue was 29.3 ± 6.9W, glandular tissue was 31.1 ± 6.1W and for malignant tissue was 49.6 ± 9.3W (Mann Whitney U p value <0.001). The average difference between impedance of malignant and glandular tissue in individual patients was 19.6 ± 8.6W.Conclusions:Our study shows a measurable difference in the dielectric properties of malignant and normal breast tissue. Our data supports the technological basis of MicroBlate®, a minimally invasive microwave ablation technology with impedance feedback, further ex-vivo studies are needed to determine its efficacy in ablating benign and malignant breast tissue. Citation Information: Cancer Res 2009;69(24 Suppl):Abstract nr 3099.