T-Scan 2000ED

Introduction

Electrical impedance scanning of the breast involves the transmission of continuous electricity into the body using either an electrical patch attached to the arm or a hand-held cylinder. The electrical current travels through the breast where it is then measured at skin level by a probe placed on the breast. Cancerous tissue conducts electricity differently than normal tissue; therefore, cancerous images may show up on the resulting imaging as a bright white spot. The T-Scan™ 2000 is an electrical impedance scanning device that received approval for marketing from the U.S. Food and Drug Administration (FDA) in 1999, with the following labeled indication: "The T-Scan™ 2000 is intended for use as an adjunct to mammography in patients who have equivocal mammographic finding with ACR Bi-RADS™ categories 3 or 4. In particular, it is not intended for use in cases with clear mammographic or non-mammographic indications for biopsy. This device provides the radiologist with additional information to guide a biopsy recommendation."

The T-Scan™ 2000 was FDA approved through the PMA process, and thus the clinical data to support its safety and effectiveness are available in the FDA summary of safety and effectiveness which is reviewed below. (2) The key pieces of data presented to the FDA were from a multicenter blinded study that intended to test the hypothesis that adjunctive combination of T-Scan™ with mammography can provide diagnostic accuracy significantly better than mammography alone.

The results of this study were reported in terms of sensitivity and specificity instead of positive and negative predictive value. The blinded study presented to the FDA consisted of a total of 2,456 patients of whom 882 underwent biopsy and T-Scan™. The mammography and T-Scan™ were performed in a blinded fashion; i.e., each imaging procedure was performed and interpreted without knowledge of the results from any other imaging modality or patient information. A final test set composed of 504 biopsied breasts (179 malignant, 325 benign) was available for re-reading (380 patients were excluded due to unavailability of the original mammogram or incomplete T-Scan™ image). The test set was re-read and scored "blindly" using T-Scan™ images alone, using mammograms alone, and using adjunctive combination of mammogram and T-Scan™ images. Each of the scores was compared against the results of biopsy. Panels of 40–60 patients each were organized for blinded rereading of the T-Scan™s and mammograms. The panels were composed of patients with both malignant and benign biopsy results, as well as screening patients that did not undergo biopsy.

The screening patients were added to the panels so that the readers could not assume that all patients had suspicious mammographic findings. The key subgroup was the 273 patients with equivocal mammographic abnormalities. These included Bi-RADS™ 3 and some Bi-RADS™ 4 cases, in which the probability of malignancy was estimated to be between 0 and 50%. Using biopsy results as the gold standard, the sensitivity of the combined mammogram and T-Scan™ compared to mammogram alone increased from 60% to 82%, while the specificity increased from 41% to 57%. Both of these are statistically significant increases. However, it is unclear from this study if these diagnostic parameters would enable patients with equivocal mammographic abnormalities to forego biopsy. Recalculating the data reveals that the key parameter of the negative predictive value of the combined test is 93%. Therefore, if the decision to forego biopsy was based on a negative result of the combined mammogram and T-Scan™, 7% of those with malignant lesions would miss or delay a diagnosis of breast cancer.

As noted, this study included some Bi-RADS™ 3 or 4 lesions, but it is not specified whether the biopsies were performed in these subjects as part of the study protocol or based on clinical suspicion and/or imaging results. The analysis of diagnostic performance included only those patients who were scheduled for biopsy, which introduces the potential for verification bias. It is uncertain whether these selected cases would be similar to unselected consecutive cases of Bi-RADS™ 3 or 4 lesions that would not be referred for biopsy in clinical practice. The positive predictive value of adjunctive use of the T-Scan™ was reported to be 30% among biopsied subjects with Bi-RADS™ 3 or 4 lesions and an 18% prevalence of malignancy. However, the limitations and potential bias in this analysis prohibit conclusions regarding the effectiveness of using the T-Scan™ in positively selecting patients for biopsy. For example, it is unknown how many of the original 2,456 patients had equivocal lesions and decided to forego biopsy. This is the critical group to evaluate the role of the T-Scan™ to positively select those patients for biopsy who would otherwise forego biopsy. While this unselected population and outcome are admittedly more difficult to study, ideally one would like to design a trial in which all patients with equivocal lesions, which would otherwise be referred for follow-up imaging, undergo both T-Scan™ and biopsy or some other appropriate reference standard such as prolonged clinical follow-up. In this setting, the diagnostic performance and predictive value of T-Scan™ could be evaluated in the actual intended use.