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US-guided Core-Needle Biopsy of the Breast: How Many Specimens Are Necessary?¹

¹ From the Departments of Radiology (J.E.F., R.R., M.V.V., G.A.) and Pathology (C.M.), University of Miami School of Medicine, Jackson Memorial Hospital Rm WW279, 1611 NW 12th Ave, Miami, FL 33136. Received October 2, 2001; revision requested November 20; revision received May 16, 2002; accepted July 24. Address correspondence to J.E.F. (e-mail: jfishman@med.miami.edu).

	ABSTRACT

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PURPOSE: To analyze the diagnostic yield for each specimen obtained at 14-gauge ultrasonography (US)-guided breast biopsy and compare these findings with mass, procedural, and specimen characteristics that could affect yield.

MATERIALS AND METHODS: Seventy-three consecutive biopsies of breast masses were performed by using a 14-gauge handheld biopsy device. Each specimen was graded for whether it was nonfragmented or fragmented and for whether it sank or floated, and each pass was graded for whether or not the needle passed through the lesion. Each specimen was mounted on a separate slide. A pathologist who was unaware of the final diagnoses reviewed the slides in random order. A diagnosis was determined for each specimen whenever possible, and diagnostic yield was calculated as a function of number of passes. The Fisher exact test was used to compare yield for different specimen characteristics.

RESULTS: Fourteen (19%) lesions were malignant and 59 (81%) were benign. Cells indicating the final diagnosis were contained in 249 (75%) of 334 specimens. Cells indicating the diagnosis were contained in the first specimen in 51 (70%) lesions, in the second specimen in 67 (92%), in the third specimen in 70 (96%), and in the fourth specimen in 73 (100%). Of the 14 malignancies, 13 (93%) were diagnosed with cells contained in the first or second specimen; one cancer (ductal carcinoma in situ) was diagnosed with cells contained in the fourth specimen. Specimens that were nonfragmented (P < .001) and sank (P < .001) showed correlation with being diagnostic, but needle visualization within the lesion did not.

CONCLUSION: A minimum of four specimens, preferably those that are nonfragmented and that sink, should be obtained with 14-gauge US-guided breast biopsy.

© RSNA, 2003

Index terms: Breast, biopsy, 00.1261 • Breast, US, 00.1298 • Breast neoplasms, diagnosis, 00.1261

	INTRODUCTION

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Ultrasonography (US)-guided core-needle biopsy of the breast is a commonly performed alternative to surgical biopsy in patients with breast masses and other lesions that are visible at US (1,2). When a lesion is equally well depicted with mammography and US, US guidance is often preferred for many reasons, including shorter procedure time, improved patient comfort, and lack of ionizing radiation (3). Most authors suggest that five core specimens be obtained during US-guided core-needle biopsy (1,3,4), but this has not been universal practice (5). Researchers in several studies (6,7) have addressed this question regarding stereotactic guidance and have determined that five specimens are required for a 99% yield when a 14-gauge needle is used for biopsy of masses. To our knowledge, no comparable study for US-guided biopsy has been performed. Factors that may influence the decision of how many specimens to obtain, such as the size of the mass or the quality of visualization of the needle passing through the lesion, have also not been addressed. The purpose of our study was to analyze the diagnostic yield for each specimen obtained at 14-gauge US-guided breast biopsy and to compare these findings with mass, procedural, and specimen characteristics that could affect yield.

	MATERIALS AND METHODS

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Patients
We performed a prospective study of consecutive patients who were referred for US-guided core-needle biopsy of at least one breast mass during a 7-month period. As part of informed consent prior to biopsy, all patients consented to research use of their biopsy specimens. Our institutional review board determined that this project was exempt from requiring additional informed consent. During the study, 79 lesions in 75 patients were sampled for biopsy. Four lesions were excluded from subsequent analysis: Three lesions were cysts that decompressed after biopsy, and pathologic material from one lesion was unavailable for review. Eighteen (24%) of the remaining 75 lesions were palpable. In eight of these cases, results of fine-needle aspiration performed by a clinician were suggestive of a diagnosis but nondiagnostic. In the 10 remaining cases, the lesion was determined to be palpable at US-guided biopsy but had been considered insufficiently palpable by the clinician to perform fine-needle aspiration without US guidance.

Procedure
Before the lesions were sampled for biopsy, lesion size was determined on US images by using the single largest dimension. Biopsies were performed by a radiology resident or fellow (R.R.) with the direct supervision and participation of one of the authors (J.E.F., M.V.V.) or another attending radiologist in our breast health center. Freehand US with a 12-MHz transducer (Diasonics, Santa Clara, Calif) was used to guide a 14-gauge automated gun with a 23-mm throw (Bard Monopty; C.R. Bard, Covington, Ga). In 18 cases (24%), a coaxial method was used with a 13-gauge cannula (4). We attempted to perform five passes for each lesion (unless complications developed or the patient refused) and obtained specimens from several regions of the lesion. For each pass, the longitudinal image obtained after deployment of the biopsy needle but before needle removal (postfire image) was evaluated to determine whether the needle passed through the lesion. Each specimen was washed off the needle into a small volume of saline, and the specimen was classified as intact (>1 cm of uninterrupted length) or fragmented. Finally, we noted whether the specimen sank to the bottom of the saline, floated, or only partially sank. Each specimen was filtered through a fine mesh envelope to extract it from the saline, and the envelope with its specimen was then placed in an individually numbered cassette corresponding to the pass number. The cassettes were placed in formalin and submitted to the pathology department. Each specimen was placed on a single slide, which was labeled with the pathology specimen identifier and pass number.

Analysis
One pathologist (C.M.), who worked independently and was unaware of the official pathology report, reviewed the slides for all patients and passes in random order. Each slide was either given at least one specific diagnosis or labeled as nondiagnostic. The diagnoses were tabulated for each lesion. Two cases were excluded from subsequent analysis because the blinded individual slide review yielded a different diagnosis than did the official pathology report. A determination that the official pathology report was correct was decided in conference with consensus. Thus, the study included a total of 73 lesions in 70 patients.

The following data were tabulated for each lesion: the lesion size (largest single dimension), the total number of passes, the number of the first pass at which cells indicating the diagnosis were contained in the specimen, and the total number of passes at which cells indicating the diagnosis were contained in the specimen. In five cases, there were two benign diagnoses. The number of the first pass at which cells indicating at least one of the diagnoses was contained in the specimen and the total number of passes at which cells indicating one, the other, or both of the benign diagnoses were contained in the specimen were used for analysis. For all passes in each patient, the characteristics of needle visualization, specimen integrity versus fragmentation, and specimen density (sinking vs floating) were tabulated.

Statistical Evaluation
Overall and parameter-specific diagnostic yields were calculated, and comparisons were determined by using the Fisher exact test. A two-tailed P value of .05 or less was indicative of statistical significance. Positive predictive values for specimens with the assessed characteristics that yielded a diagnosis were calculated. For patients with benign biopsy results who did not undergo excision, follow-up imaging or cross-reference with hospital, state, and national cancer databases was performed to determine whether malignant disease was subsequently diagnosed (ie, false-negative findings at biopsy).

	RESULTS

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Of the 73 lesions, 14 (19%) were malignant. There were 11 infiltrating ductal carcinomas; one metastatic carcinoma in a lymph node; and two cases of ductal carcinoma in situ, which were confirmed at surgery as noninvasive. In the remaining 59 lesions, diagnoses were benign in 64, and the most common of these were fibroadenoma (n = 40, 55% of all lesions), fibrocystic change (n = 14, 19% of all lesions), and focal fibrosis (n = 4, 5% of all lesions). Other benign diagnoses included benign sclerosing lesions (n = 3), papillomas (n = 2), and fat necrosis (n = 1). In five benign lesions, cells indicating two diagnoses were contained in the specimens. The average size of all lesions was 1.7 cm (median, 1.5 cm; range, 0.6–6.0 cm), the average size of malignancies was 1.9 cm (median, 1.6 cm; range, 0.9–3.5 cm), and the average size of benign lesions was 1.6 cm (median, 1.5 cm; range, 0.6–6.0 cm).

Three hundred thirty-four core specimens were obtained (mean, 4.6 per lesion). Among all lesions, cells indicating the final diagnosis were contained in 249 (75%) specimens. Coaxial biopsy was used to obtain 87 specimens in 18 lesions; findings in 62 (71%) specimens were diagnostic. This finding did not differ significantly from that obtained in 187 (76%) of 247 specimens in which coaxial biopsy was not used (P = .47). For malignancies, cells indicating the diagnosis were contained in 43 (73%) of 59 specimens. Among all 73 lesions, cells indicating the diagnosis were contained in the first specimen in 51 (70%), in the second specimen in 67 (92%), in the third specimen in 70 (96%), and in the fourth specimen in all 73 (100%). For the 18 lesions sampled with coaxial biopsy, cells indicating the diagnosis were contained in the first (61%) or second (89%) specimen in 16 cases; they were contained in the fourth specimen in two cases. For lesions 1 cm or smaller (14 lesions, 19% of all cases), cells indicating the diagnosis were contained in the first specimen in eight (57%), in the second specimen in 11 (78%), in the third specimen in 12 (86%), and in the fourth specimen in all 14 (100%). For malignancies, cells indicating the diagnosis were contained in the specimens in 13 of 14 cases in the first (64%) or second (93%) specimen; one case of ductal carcinoma in situ did not have cells indicating the diagnosis until the fourth specimen. There were no statistically significant differences between the results for lesions sampled with coaxial versus uniaxial biopsy, small versus large lesions, or malignant versus benign lesions. The closest values to statistical significance were for whether cells indicating the diagnosis were present in the specimens removed within the first three passes, in which case P = .15 for lesions sampled with coaxial versus uniaxial biopsy, P = .09 for small versus large lesions, and P = .48 for malignant versus benign lesions.

The Table lists the distribution of specimens both with and without the assessed characteristics (needle visualization, integrity of the specimen, and density of the specimen [whether the specimen sank or floated]), with respect to whether the specimen was diagnostic or not. Of all 334 specimens, 249 (75%) were diagnostic. In 305 (91%) specimens, the needle was visualized to pass through the lesion, but needle visualization did not help distinguish whether a specimen would be diagnostic. We obtained the same yield among passes in which the needle was observed to have passed through the lesion for lesions 1 cm or smaller and lesions larger than 1 cm (75% positive yield in each case). Conversely, both intact specimens and dense specimens were significantly associated with being diagnostic (P < .001 for both). Of the 334 specimens, 237 (71%) were intact and 266 (80%) sank completely in saline. The positive predictive values for intact and dense specimens were 81% and 82%, respectively. Specimens that were both intact and sank accounted for only 59% of the total specimen pool, but that combination of parameters had the highest positive predictive value (86%) for a determination of the diagnosis.

	DISCUSSION

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US-guided core-needle biopsy of the breast is an accepted technique for diagnosing breast abnormalities, and it can help patients avoid exposure to the ionizing radiation of stereotactic guidance and the higher morbidity, cost, and mammographic sequelae of surgical excision. As with stereotactic methods, US-guided procedures can be performed by using a variety of techniques (eg, varying needle sizes, number of passes, and uniaxial vs coaxial methods). Reasons to obtain a sufficient, but not excessive, number of biopsy specimens include the minimization of procedure time, patient discomfort, and breast trauma. Although the required minimum number of samples obtained with stereotactic guidance has been investigated (6,7), the corresponding study for US guidance has not, to our knowledge, been performed. There are differences between stereotactic and US-guided procedures, such as the nature of the lesions sampled for biopsy (masses vs calcifications), the needle choice (size, vacuum assisted vs non–vacuum assisted), and the effect of operator experience. All of these differences argue against extrapolation of stereotactic diagnostic yields to US methods.

Of the variables we examined, intact specimens and those that sank showed correlation with diagnostic yield. These characteristics are easily assessed at biopsy. Specimen density can also be evaluated by using radiography, and dense specimens have been shown to be more highly diagnostic than low-density specimens (8). Needle visualization within a lesion may be somewhat more subjective and can be influenced by partial-volume effects toward the periphery of a lesion. With use of longitudinal (along the needle) postfire images, only 9% of the passes were considered to have missed the lesion, and this may limit our ability to detect a diagnostic difference on the basis of needle position. Postfire needle position can be more precisely evaluated by obtaining an image in the orthogonal plane before the needle is removed from the patient (1), but this was not routinely performed in our study. It might be expected that the occurrence of partial-volume averaging errors during the assessment of needle position might further reduce the yield for small lesions. We encountered a small but statistically insignificant difference in yield per pass between smaller and larger lesions. Our institution is a teaching hospital, and the residents become actively involved in these procedures at an early stage in their training. This necessitates more two-person biopsy performance than in practices with more experienced radiologists, which may affect the accuracy of lesion targeting (3). We also did not observe differences in the number of specimens necessary to diagnose malignant versus benign lesions.

Our study is limited by the lack of follow-up imaging in 21 of the 59 patients with benign lesions. Although we cross-referenced these patients with local and national cancer registries to check for false-negative biopsy results, reporting rates to such databases vary. At the time of publication of this article, it has been more than 2 years since the end of the study. Although we could have considered delaying the release of our results pending more follow-up data, our experience is that few patients will return for imaging after more than a 2-year hiatus.

In this study, cells indicating more than 90% of benign and malignant diagnoses were contained in specimens removed at the first or second pass when 14-gauge US-guided core-needle biopsy of the breast was performed. Cells indicating a diagnosis were contained in the first, second, third, or fourth specimen in every case, and four passes are the minimum number we recommend for this procedure. Yield was equivalent whether specimens were obtained coaxially or not. High specimen density and intact specimens were important characteristics for predicting yield, but postfire needle position verification was not.

	ACKNOWLEDGMENTS

 
We thank David Schwartz, MD, Humberto Martinez, MD, and Richard Kiszonas, DO, for biopsy supervision. We also gratefully acknowledge Michelle McDonald, RT, for technical assistance and Maria Anton for secretarial assistance.

	FOOTNOTES

 
Author contributions: Guarantor of integrity of entire study, J.E.F.; study concepts and design, J.E.F., C.M., R.R.; literature research, J.E.F., R.R.; clinical studies, J.E.F., R.R., M.V.V.; data acquisition, all authors; data analysis/interpretation, J.E.F., M.V.V., G.A.; statistical analysis, J.E.F.; manuscript preparation, J.E.F.; manuscript definition of intellectual content, editing, revision/review, and final version approval, all authors.

	REFERENCES

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4. Kaplan SS, Racenstein MJ, Wong WS. US-guided core biopsy of the breast with a coaxial system. Radiology 1995; 194:573-575.[Abstract/Free Full Text]
5. Mitnick JS, Gianutsos R, Pollack AH, et al. Tubular carcinoma of the breast: sensitivity of diagnostic techniques and correlation with histopathology. AJR Am J Roentgenol 1999; 172:319-323.[Abstract/Free Full Text]
6. Liberman L, Dershaw DD, Rosen PP. Stereotaxic 14-gauge breast biopsy: how many core biopsy specimens are needed? Radiology 1994; 192:793-795.[Abstract/Free Full Text]
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