Bioimpedance: Novel use of a minimally invasive technique for cancer localization in the intact prostate

BACKGROUND. Prostate cancer is presently diagnosed by transrectal ultrasoun d (TRUS)-guided sextant needle biopsy. While echo texture of the tissue can prompt localization of tumor, it is presently imprecise. From 59-75% of me n biopsied, based on an abnormal digital rectal examination (DRE) or elevat ed prostate-specific antigen (PSA) level, have negative biopsy results. Imp rovements in tumor localization during TRUS-guided prostate biopsy are grea tly needed. Bioimpedance is an electrical property of biologic tissue. Elec tric current is limited in living tissue by highly insulating cell membrane s; however, different tissue architecture such as cancer may impede current differently and allow detection of differences between normal and abnormal or malignant prostate tissue. Our goal was to assess the utility of bioimp edance measurements in differentiating tumor from normal prostatic tissue i n an ex vivo model. METHODS. Bioimpedance was measured in six ex vivo prostates, which were rem oved for clinically localized prostate cancer. Two bioimpedance needles, 1 mm apart, were inserted 3 mm into the posterior surface of the prostate an average of 16 times per gland. Frequencies ranging from 100 kHz-4 MHz were used to obtain 594 bioimpedance measurements from the six glands. These mea surements were then correlated with histology to determine the presence or absence of prostate cancer. RESULTS. Prostate cancer was found to have a higher impedance, of 932 +/- 1 70 ohms, compared to areas of no cancer within the same prostate, 751 +/- 1 51 ohms, P < 0.0001, at 2 MHz. This phenomenon was observed across all freq uencies tested. CONCLUSIONS. This study demonstrates for the first time application of bioi mpedance to distinguish areas of prostate cancer from areas of normal prost ate. This technology may improve identification and localization of cancer within the prostate. Moreover, bioimpedance can potentially guide needle pl acement during prostate biopsy and thus improve sampling of tumors. Current ly, our ex vivo model is limited by variables such as temperature and lack of blood flow. Further studies in an in vivo model will be needed to assess their effect. (C) 1999 Wiley-Liss, Inc.