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1 Good Samaritan Breast Care Center, Radiological Associates Medical Group, 2410 Samaritan Dr., Ste. 101, San Jose, CA 95124.
Received September 16, 1999;
accepted after revision February 8, 2000.
Address correspondence to R. L. Smathers, Mammography Specialists Medical
Group, Inc., 15559 Union Ave., Ste. 6, PMB 230, Los Gatos, CA 95032.
Abstract
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MATERIALS AND METHODS. One hundred one consecutive ABBI biopsies were reviewed. The ABBI specimen radiographs were used to measure the area occupied by the entire specimen, the area excluding the lesion, and the area of the lesion alone. These areas, the length, and the width of all specimens were statistically analyzed using computer software.
RESULTS. Of the 101 biopsies, histologic diagnosis was malignant in 27 and benign in 74. Of the 27 malignancies, four had negative margins and 23 had positive margins. Of the 23 with positive margins, eight were ductal carcinoma in situ (tumor within 0.5 mm or less of the surgical margin), and 15 were not ductal carcinoma in situ (tumor at the surgical margin). The average specimen length was 5.51 cm and the average width was 1.65 cm. The average percentage of lesion tissue was 9.9%.
CONCLUSION. An average of 90.1% of tissue removed by ABBI biopsies was from surrounding tissue only. Uninvolved tissue is unfortunately included because of the cylindric geometry of the ABBI cannula. The ABBI biopsy has a high percentage (85.2%) of positive margins for malignant lesions and is poor excisional tool. For diagnostic biopsies, core needle biopsy is preferable because a smaller tissue volume is resected directly from the lesion site.
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The specimen radiographs were quantitatively measured using a crosshatched millimeter grid overlay. The perimeter of the specimen and the perimeter of the lesion were outlined. The areas occupied by the entire specimen and by the lesion were measured by counting the square millimeters each area covered. The specimen radiograph measurements were all corrected for a magnification factor of 1.03 (contact radiograph). This factor was directly measured using a phantom in the specimen radiographic unit. All specimens were compressed to a relatively uniform thickness by the specimen envelope. The measured areas were thereby linearly proportional to the actual volumes. The specimen envelope consists simply of two sheets of cleared film cut to fit the specimen and taped firmly together. This envelope compresses the specimens (without damaging them) to a thickness of approximately 5-15 mm. Although the compressed thickness varied from case to case, it was fairly uniform for each individual specimen.
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For the 101 specimens in this series, the average length was 5.51 ± 2.18 cm and the average width was 1.65 ± 0.46 cm. The number of cases, the average area of specimen, the average area surrounding, the average area of lesion, and the average percentage of specimen occupied by the lesion (percentage of lesion area) are given in Table 1. These numbers are presented for each of the ABBI cannula diameter sizes used in this study. Included are averages for all cannula sizes and for each of the three specific ABBI cannula diameters (10, 15, and 20 mm). Note that the average percentage of lesion area for all cannula sizes is 9.9%. This indicates that, on the average, 90.1% of tissue removed by ABBI biopsies is surrounding tissue only. This radiographically uninvolved tissue is resected primarily because of the cylindric geometry of the ABBI cannula.
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Imagine, as shown in Figure 3A,3B, a 1-cm-diameter spherical lesion resected perfectly by a 2-cm-diameter cylindric ABBI cannula. Assume the specimen has a length of 5 cm (average in this series 5.51 cm). Figure 3A is a three-dimensional view and Figure 3B is a cross-sectional view of this cylindric specimen. The cross-sectional diagram shows the clear central circular lesion area and the cross-hatched surrounding nonlesion area. The area of the lesion in this example is 0.785 cm2. The area of the whole rectangle is 10 cm2. The nonlesion area or "dead space" is 9.215 cm2 and occupies 92.15% of the total area resected.
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Stereotactic large-core needle biopsy avoids the geometry problems of ABBI cannulas by resecting tissue only at the site of the lesion. Stereotactic large-core needle biopsy has been advocated as an alternative to excisional, diagnostic surgical biopsy (performed with wire or needle localization) in nonpalpable breast lesions detected with mammography [3].
Surgeons in this study chose a cannula diameter size on the basis of the lesion size measured on the preoperative mammograms and on the preliminary digital images. The individual surgeon's preferences and experience with the equipment also affected choice of cannula diameter. Table 1 shows that the area of specimen increases as the cannula diameter increases. Note that the percentage of lesion area increases when cannula diameter is changed from 10 to 15 mm, but decreases slightly when changed from 15 to 20 mm. This may be partly because the preoperative size of the lesion was in many cases different from the size of the lesion in the specimen. This occurred because many specimens did not include the entire lesion. The rationale for selecting and using a large-diameter (such as 20 mm) cannula is uncertain but implies an attempt to perform an excisional biopsy rather than incisional biopsy. The practice of allowing a patient to believe that ABBI will entirely remove the lesion should be strongly discouraged, especially given that the ABBI device is not approved by the FDA for excisional biopsy. An incisional biopsy can be done with a core biopsy needle faster, with less trauma, and with less expense.
In two of the 101 cases in this series, ABBI biopsy missed the lesion and a second specimen was obtained by open surgical biopsy. Another study reported 30% (14/47) of ABBI cases required conversion to open surgical biopsy for completion of the procedure [4]. One of the main reasons for missed lesions is the wire snare mechanism used at the end of the procedure. Once the ABBI cutting-knife cylinder has been fully advanced, the specimen is ready for removal except that the far end of the specimen is still attached to the breast. A built-in wire loop snare is used like a noose or garrote to squeeze off and detach the end of the specimen. In many cases, the loop does not completely cut through the end of the specimen even when cautery is used. This leaves a band of tissue that pulls on the end of the specimen while the surgeon is trying to pull out the device. Consequently, the specimen is first stretched and then torn during removal from the breast. The specimen is often fragmented, especially near the distal end. In most cases, the lesion is located near or at the distal end of the specimen, so the result may be partial or complete failure of removal of the lesion. The pulling and stretching of the specimen also causes tears and rifts in the edges of the specimen that make pathologic assessment of inked surgical margins difficult and potentially misleading.
The rate of positive margins of malignant biopsies causes concern. This study found ABBI biopsies with malignant findings had a relatively high percentage (85.2%) of positive margins. The series of Leibman et al. [5] described 54 ABBI biopsies in which tumor involving the margins of the breast specimen was found in 86% of the malignant cases. The series of Rebner et al. [6] described 90 ABBI biopsies in which positive margins were found in 64% of the malignant cases. Much of this problem is related to the geometry of the ABBI cannula. It is difficult to precisely center a 15-mm lesion in a 20-mm-diameter cannula without crossing the lesion anywhere. Cutting of the malignancy can occur at any point around the 360° circumference of the cylinder.
ABBI biopsy specimens have an average percentage of lesion area of 9.9%. On average, 90.1% of tissue removed by ABBI biopsy is only surrounding tissue. This radiographically uninvolved tissue is resected primarily because of the cylindric geometry of the ABBI cannula. The ABBI system has certain limitations and mechanical problems, and offers an advantage over diagnostic techniques in only a limited number of cases [4]. ABBI specimen results tend to be best when the lesion is small and located near the skin. Stereotactic large-core needle biopsy avoids the geometry problems of ABBI cannulas by resecting a smaller volume of tissue directly from the lesion.
Acknowledgments
I thank Jan M. Cretcher for her invaluable assistance, and I appreciate the
help of Joan Santonastasi, Renee Rockwell, Theresa Cantu-Finch, and Lee
Winick.
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