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

Background: Prostate cancer is presently diagnosed by transrectal ultrasound (TRUS)-guided sextant needle biopsy. While echo texture of the tissue can prompt localization of tumor, it is presently imprecise. From 50-75% of men biopsied, based on an abnormal digital rectal examination (DRE) or elevated prostate-specific antigen (PSA) level, have negative biopsy results. Improvements in tumor localization during TRUS-guided prostate biopsy are greatly needed. Bioimpedance is an electrical property of biologic tissue. Electric current is limited in living tissue by highly insulating cell membranes; 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 bioimpedance measurements in differentiating tumor from normal prostatic tissue in an ex vivo model.

Methods: Bioimpedance was measured in six ex vivo prostates, which were removed 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 measurements 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+/-170 ohms, compared to areas of no cancer within the same prostate, 751+/-151 ohms, P < 0.0001, at 2 MHz. This phenomenon was observed across all frequencies tested.

Conclusions: This study demonstrates for the first time application of bioimpedance to distinguish areas of prostate cancer from areas of normal prostate. This technology may improve identification and localization of cancer within the prostate. Moreover, bioimpedance can potentially guide needle placement during prostate biopsy and thus improve sampling of tumors. Currently, 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.