Six-Month Short-Interval Imaging Follow-Up for Benign Concordant Core Needle Biopsy of the Breast: Outcomes in 1444 Cases With Long-Term Follow-Up

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1 Women s Imaging Original Research Monticciolo et al. Short-Interval Imaging Follow-Up for Benign Breast Biopsies Women s Imaging Original Research Debra L. Monticciolo 1 Rodney L. Hajdik 1 Mason G. Hicks 1 June K. Winford 1,2 William R. Larkin 1 James V. Vasek, Jr. 1 Brandon M. Ashton 1 Monticciolo DL, Hajdik RL, Hicks MG, et al. Keywords: breast core needle biopsy, breast imaging, breast ultrasound, stereotactic breast biopsy DOI: /AJR Received vember 4, 2015; accepted after revision April 16, Section of Breast Imaging, Department of Radiology, Baylor Scott & White Health of Texas A&M University, 2401 S 31st St, MS-01-W256, Temple, TX Address correspondence to D. L. Monticciolo (Debra.Monticciolo@BSWHealth.org) 2 Present address: Radiology Associates of Atlanta, Atlanta, GA. This article is available for credit. AJR 2016; 207: X/16/ American Roentgen Ray Society Six-Month Short-Interval Imaging Follow-Up for Benign Concordant Core Needle Biopsy of the Breast: Outcomes in 1444 Cases With Long-Term Follow-Up OBJECTIVE. The purpose of this study is to assess whether 6-month imaging follow-up after benign core needle breast biopsy is important for patient outcomes and whether it depends on nonspecific versus definitive benign biopsy results. MATERIALS AND METHODS. Consecutive breast biopsies from 2003 to 2010 were analyzed. Benign concordant lesions with at least 2 years of follow-up were assessed. Pathologic abnormalities were further characterized as having definitive or nonspecific features. A two-tailed Fisher exact test was used to assess the difference in pathologic features among lesions that had progressed. RESULTS. Of 3256 cases, 1705 biopsies in 1602 women were benign concordant and were recommended for 6-month imaging follow-up; the compliance rate was 94.9%. Of these, 1444 biopsies were confirmed as benign with long-term follow-up or excision. At pathologic analysis, 805 (55.7%) benign lesions had definitive features and 639 (44.3%) had nonspecific features. Thirty-four (2.4%) lesions progressed; this was similar for the lesions with definitive (2.6%) and nonspecific (2.0%) features (p = 0.60). The false-negative rate was 0.18%, with a mean of 5.0 cores sampled per lesion. CONCLUSION. For lesions with benign concordant biopsy results, selection of the follow-up interval should not be dictated by whether the pathologic features are definitive or nonspecific. The number of lesions that progress at imaging follow-up is low. The false-negative rate is low, regardless of modality or lesion type. A low false-negative rate is achievable with a reasonable number of core samples. The 6-month follow-up interval benefits only a small number of patients. Our results suggest that routine imaging after core needle biopsy is safe. M inimally invasive breast biopsy has become a standard diagnostic tool for tissue characterization of breast lesions. The success of core needle biopsy in the diagnosis of breast lesions is largely the result of the accuracy achieved with minimal risk [1]. Core needle biopsy diagnosis can be performed with ultrasound, stereotactic, or MRI guidance. Needle biopsy results that reveal malignancy allow prompt treatment planning. High-risk lesions, such as lesions with atypia, radial scars, phyllodes tumors, and papillary lesions, will often require further immediate management. Discordant results will trigger repeat biopsy. Benign concordant results allow the patient to return to imaging follow-up. Benign concordant results make up a large portion of needle biopsy results [2]. The follow-up interval for benign concordant results is a matter of debate. Recommendations vary from 6-month short-interval follow-up and then a return to screening to follow-up imaging at 6, 12, 24, and 36 months [3 9]. It has also been suggested that follow-up intervals could be based on the biopsy results, with only nonspecific benign diagnoses needing the initial 6-month follow-up [6]. The intent of the short-interval follow-up is to confirm stability and to discover false-negative lesions as early as possible. This has been shown to be necessary for MRI-guided biopsy, the newest of the needle biopsy techniques [10, 11]. Ultrasound and stereotactic guidance are more mature, having been widely available since the early 1990s [12]. Recent reports suggest that a 6-month follow-up examination is not needed with ultrasound or stereo guidance when the results are benign and concordant with the imaging findings [7, 8]. In our practice, we routinely suggest short-interval follow-up after benign concordant results. The purpose of this study is to assess whether the 6-month fol- 912 AJR:207, October 2016

2 Short-Interval Imaging Follow-Up for Benign Breast Biopsies low-up examination is important for patient outcomes and whether the need for short-interval follow-up is related to nonspecific versus definitive biopsy results. Materials and Methods Informed consent was waived for this HIPAAcompliant study, which was approved by the institutional review board at Scott & White Clinic (now Baylor Scott & White Health) of Texas A&M University. The study is a retrospective review of consecutive image-guided needle biopsies performed by the section of breast imaging from January 1, 2003, through January 1, 2010, with follow-up through February All stereotactic- and ultrasound-guided core needle biopsies performed during the study period were included; a small number of MRI-guided biopsies were also evaluated because they were erroneously described in the structured reporting database used to capture the biopsy events. This represents a minority of MRIguided cases, because a separate database is typically used for those biopsies. The evaluated MRI cases were, therefore, excluded from this analysis. All biopsies were performed or supervised by attending physicians working in the breast imaging section with 5 25 years experience. All patients were recommended for biopsy because of suspicious imaging findings, with or without clinical symptoms. Stereotactic-guided biopsies were performed on a dedicated prone table, and vacuum-assisted core needles were used in all cases, in a range of sizes (either 9, 11, or 12 gauge). All ultrasound-guided biopsies were performed with a handheld 14-gauge spring-loaded device. Various types and brands of biopsy marking clips were used during the study time frame, with two-view mammography obtained after the procedure to document clip placement. Biopsy markers were placed at the discretion of the radiologist early in the study but became routine as the study period progressed. Specimen radiographs were obtained on all biopsies performed for calcifications. All pathologic results were reviewed by the radiologist who performed the biopsy to confirm concordance. Any cases of discrepancy were reviewed with other members of the breast imaging section or the pathologist, as needed. All cases were classified into one of the following categories: malignant, high risk, benign discordant, benign concordant, cyst contents, or lost to followup. High-risk lesions included those typically referred for surgical evaluation at our institution, such as atypical ductal hyperplasia, lobular neoplasia (including atypical lobular hyperplasia and lobular carcinoma in situ), flat epithelial atypia, radial scar or complex sclerosing lesion, papilloma or papillary lesion (excluding papillomatosis), and 1064 High risk* Total 3256 Benign discordant phyllodes tumor. Benign discordant lesions were those in which the benign pathologic findings did not adequately account for the imaging findings. The cases lost to follow-up included those in which no follow-up imaging was performed or cases of patients who went on to mastectomy, unilateral or bilateral, for other reasons without definite correlation for the benign biopsy site. We considered in our compliance calculations all patients who had initial benign concordant biopsy results and were recommended for short-interval followup. However, our final analysis includes only those cases for which we have 24 or more months of imaging follow-up, or 4 or more years of clinical follow-up, or excisional biopsy to confirm benignity. Benign concordant results were categorized as definitive or nonspecific according to pathologic findings. Definitive diagnoses were those of a specific entity that could account for the lesion and included fibroadenoma (which includes lesions described at pathologic analysis as fibroadenoma, features of fibroadenoma, or fibroadenomatous nodule), tubular adenoma, hematoma or inflammation, abscess, hamartoma (fibroadenolipoma), fat necrosis, granulomatous disease, lymph node, myofibroma, cyst contents, and pseudoangiomatous stromal hyperplasia. Benign nonspecific results included fibrocystic changes, fibrous mastopathy, apocrine metaplasia, duct hyperplasia, and stromal fibrosis. If multiple pathologic abnormalities were noted for a lesion and at least one was definitive, the case was characterized as definitive. All biopsy cases consecutively entered into our structured reporting system for breast imaging for the 7 years of January 1, 2003, through January 1, 2010, were reviewed for this report. Our radiology structured reporting system records the date of the biopsy, modality, laterality and location, lesion size, lesion type (which we categorized as mass, calcifications, or architectural distortion), needle gauge, the number of samples obtained for each lesion, and the presence or absence of calcifications in the specimen radiograph of all calcified lesions. A separate electronic medical record was reviewed for each patient recording pathologic results, imaging, and clinical follow-up relevant to the case. From the imaging reports, the exact dates of imaging were recorded, as well as a designation of stable, decrease, or increase in size of the biopsied lesion and recommendation to continue screening, to biopsy, or for other management. Any imaging report that suggested a change in the index lesion was carefully evaluated; if there was concern that a finding might not correspond to the index lesion, the images were directly reviewed. Lesions were considered to be if there was a significant change in mass size (as determined by the radiologist), number of calcifications, or other signs of lesion progression. When the pathology reports became available, concordance was determined by the radiologist who performed the procedure. A false-negative was defined as a lesion proven to be cancer after a result was reported as benign and concordant at core needle biopsy. False-negative results were all evaluated with complete review of records and images from prebiopsy, biopsy, and follow-up examinations. The number of total cancers diagnosed by needle biopsy during the study period was used to calculate the false-negative rate. If a patient returned for imaging at 4 9 months after biopsy, the visit was recorded as complying with the 6-month short-interval biopsy follow-up imaging. Lesion stability with at least 24 months of follow-up imaging or at least 4 years of benign clinical follow-up was taken as confirmation of benignity. Surgical excision, in spite of the recommendation for imaging follow-up, was also used to confirm benignity in some cases. Tumor registry linkage was not performed. We assessed the null hypothesis of no association between pathologic findings and lesion progression using a two-sided Fisher exact test, and a Benign concordant Other** 412 * Includes cases with lobular or ductal atypia, radial scar or complex sclerosing lesion, phyllodes tumors, and papillary lesions. ** Includes 90 lost to follow-up, 36 cyst contents or fine-needle aspiration, 25 other modality, and 261 benign concordant who returned but had less than 2 years of follow-up. Fig. 1 Chart of core needle biopsy breast biopsy results for January 1, 2003, through January 1, AJR:207, October

3 Monticciolo et al. TABLE 1: Benign Lesions at Breast Core Needle Biopsy: Pathologic Category Versus Lesion Behavior at Follow-Up Pathologic Category Lesion Stable Lesion Increased Total Definitive 784 (97.4) 21 (2.6) 805 nspecific 626 (98.0) 13 (2.0) 639 Total 1410 (97.6) 34 (2.4) 1444 te Data are number (%) of lesions. type I error rate of We provided an odds ratio and asymptotic 95% CIs. Results We reviewed 3256 consecutive core needle biopsy cases recorded in our structured reporting system during a 7-year period. Of these, 1064 (32.7%) were malignant, 212 (6.5%) were high risk, 124 (3.8%) were benign but discordant, 36 (1.1%) were benign fine-needle aspiration cyst or abscess contents, 25 (0.8%) were mislabeled MRI cases, and 90 (2.8%) were benign but were lost to follow-up by the criteria outlined already (Fig. 1). The remaining 1705 benign concordant cases in 1602 women were labeled benign concordant at initial biopsy; the patients were asked to return for short-interval follow-up and returned for at least some followup, either imaging or clinical. Of these, 1444 biopsy cases in 1356 women had adequate follow-up (at least 2 years of imaging followup, 4 or more years of clinical follow-up, or excisional biopsy). These cases constitute the main study population for this report. The mean patient age at the time of biopsy was 53 years (range, years); 1302 women had one biopsy, 61 had two biopsies, four had three biopsies, and two had four biopsies. Of the 1444 biopsies, the lesion type was mass in 1213 (84.0%) cases and calcifications in 231 (16.0%) cases. The mean lesion size was 1.2 cm (SD, 0.7 cm; range, cm). Ultrasound was used as the imaging modality in 1147 (79.4%) cases and stereotactic guidance was in 297 (20.6%) cases. All stereotactic biopsies used vacuum assistance; 103 (34.7%) were performed with a 9-gauge needle, 187 (63.0%) used an 11-gauge needle, and seven (2.4%) used a 12-gauge needle. All ultrasound biopsies were performed with a 14-gauge spring-loaded needle. The mean number of cores obtained per lesion was 5.0 (SD, 1.1 core; range 1 13 cores). By modality, the mean number of cores is as follows: for ultrasound, 5.1 cores (SD, 1.1 core; range, 1 10 cores) and for stereotactic imaging, 4.6 cores (SD, 1.5 core; range, 2 13 cores). Of the 1602 women asked to return for short-interval follow-up after the benign concordant results, 182 opted for immediate excision (11.4%), all with benign results. Of the remaining 1420 women available to return for lesion assessment with imaging, 1348 were compliant with our recommendation for a 6-month imaging follow-up, for a compliance rate of 94.9%. Of the 1444 lesions biopsied with benign concordant results, benignity was confirmed with excision or imaging of 2 years or more in 1358 (94.0%) cases. Clinical follow-up of 4 years or more was obtained for the remaining 86 (6.0%) lesions. Mean imaging follow-up was 69 months (SD, 27 months; range, months), and mean clinical follow-up was 5.4 years (SD, 1.6 years; range, years). The mean follow-up for all cases (imaging or TABLE 2: False-Negatives and Benign but Actionable Results at Follow-Up for Lesions Diagnosed as Benign at Core Needle Biopsy Case. Lesion Type Modality Total. of Cores Initial Pathologic Diagnosis Follow-Up 1 Mass Ultrasound 5 Fibrocystic changes 6 mo imaging; 2 Calcifications Ultrasound 5 Fibrosis with microcalcifications 4 mo imaging; stable; at 17 mo 3 Mass Ultrasound 5 Duct hyperplasia Patient requested excision 4 Mass Ultrasound 5 Fibrosis 6 mo imaging; Pathologic Diagnosis at Excision Invasive ductal carcinoma Ductal carcinoma in situ Lobular carcinoma in situ Fibroadenoma and atypical ductal hyperplasia Comment Should have been labeled discordant calcifications in specimen x-ray Subsequent mastectomy was negative Same patient as case 6 5 Mass Ultrasound 5 Fibrosis 6 mo imaging; stable Fibroadenoma and Reexcision benign atypical ductal hyperplasia 6 Mass Ultrasound 5 Fibroadenoma 1 y imaging; Phyllodes tumor Low grade 7 Mass Ultrasound 5 Fibroadenoma 6 mo imaging; Phyllodes tumor Low grade 8 Mass Ultrasound 5 Fibroadenoma 6 mo imaging; Phyllodes tumor Low grade 9 Mass Ultrasound 5 Fibroadenoma 6 mo imaging; Phyllodes tumor Low grade 10 Mass Ultrasound 6 Fibroadenoma 6 mo imaging; stable; at 2 y Phyllodes tumor Low grade; found on physical examination False- Negative Yes Yes 914 AJR:207, October 2016

4 Short-Interval Imaging Follow-Up for Benign Breast Biopsies clinical or both) was 5.7 years (SD, 1.8 years; range, years). At pathologic analysis, 805 (55.7%) cases were considered definitive and 639 (44.3%) were labeled nonspecific benign, as outlined already. The most common definitive diagnosis was fibroadenoma (606 lesions; 75.3% of definitive cases and 42.0% of all benign concordant lesions). Overall, 34 lesions (2.4%) in size at the first imaging follow-up examination (Table 1). In 27 of these cases, the first imaging examination was within the recommended 6-month follow-up window; one patient returned earlier and six returned later than expected. In the benign definitive group, 2.6% (21/805) of lesions in size, whereas in the benign nonspecific group, 2.0% (13/639) of lesions in size. We could not conclude that there was any association between pathologic findings and further lesion growth (p = 0.60, Fisher exact test). Reflecting the nonsignificance of the p value, the odds ratio for progression versus nonprogression of those lesions with benign definitive findings versus those with benign nonspecific findings was 1.28 (95% CI, ). The lesions that over time included a mass in 33 (97%) of 34 cases and calcifications in one (3%) case. All but one of the masses was diagnosed with ultrasound guidance (one with stereotactic biopsy). Seventeen of the lesions that enlarged were diagnosed at needle biopsy as fibroadenoma, which constituted 50% (17/34) of all progressive lesions. Of the 1444 lesions with presumably benign pathologic findings, 34 showed growth after 6 months of follow-up. At biopsy, two of the 34 were found to be malignant, for a false-negative rate of 0.14% for study cases (95% CI, %). During the study period, 1119 malignancies were diagnosed as a result of needle biopsy, including those among discordant and high-risk cases, for an overall false-negative rate of 0.18%. The first false-negative was a 3.3-cm mass biopsied with ultrasound. Five cores were obtained and revealed nonspecific benign pathologic features (fibrocystic changes and adenosis). The patient returned for 6-month imaging follow-up as recommended, and the lesion had to 6 cm. Excision showed invasive ductal carcinoma. Review of the imaging for this case showed that the initial pathologic finding should have been labeled discordant; the nearly anechoic oval mass had indistinct margins and was highly suspicious of malignancy. Review of the biopsy images also suggests poor lesion sampling, as determined by the needle position in relation to the mass. The other false-negative involved calcifications biopsied with ultrasound because stereotactic-guided biopsy could not be performed (breast too thin in compression). calcifications were seen on specimen radiograph, but fibrosis, with microcalcifications, was diagnosed at pathologic analysis. The patient returned for short-interval follow-up at 4 months, and the lesion was stable at mammography. On a subsequent 17-month followup examination after the initial biopsy, new calcifications were seen adjacent to the previously biopsied cluster. It was clear on the surgical specimen that these new calcifications were an extension of the initial target. Ductal carcinoma in situ was the diagnosis. There were eight additional lesions with important, though nonmalignant, findings at follow-up (Table 2). Three of the eight were ultrasound-guided biopsies found to be highrisk atypia or lobular neoplasia at excisional biopsy. Two of these were masses that occurred in the left upper outer breast of one patient, measuring 1.3 and 1.2 cm. Both lesions were diagnosed as fibrosis (nonspecific benign) at core biopsy. At the 6-month follow-up examination, the 1.3-cm lesion was in size and the 1.2-cm lesion was stable. Both were excised. The final pathologic finding for the 1.3-cm mass was fibroadenoma with a small focus of atypical ductal hyperplasia. The stable 1.2-cm lesion had a final pathologic finding of fibroadenoma with florid atypical ductal hyperplasia, possibly ductal carcinoma in situ. Reexcision at both sites showed no malignancy or remaining atypia. The third high-risk lesion was a 0.8-cm mass diagnosed on needle biopsy as duct hyperplasia without atypia. The patient requested excisional biopsy, which showed lobular carcinoma in situ. Subsequent mastectomy for other reasons was free of tumor. The remaining five of the eight lesions requiring additional attention had undergone ultrasound-guided biopsy; all of them were diagnosed as fibroadenoma on core needle biopsy and later were found to be benign phyllodes tumors. These represent 0.8% (5/606) of all fibroadenomas diagnosed with a core needle biopsy technique during the study. In three of these cases, the lesion was noted to be at 6-month follow-up examination, prompting excision. The fourth lesion was stable at 6-month imaging but was found to be on physical examination 2 years later and was excised. The final patient missed her 6-month follow-up examination but returned at 1 year, and the lesion had in size, leading to excision. All five phyllodes lesions were low grade. Discussion The use of core needle biopsy in the diagnosis of breast lesions is widely accepted because of its accuracy, speed, low complication rates, and cost advantages [13 15]. In spite of years of clinical use, however, there is no consensus on imaging follow-up after needle biopsy. It is understood that core needle biopsy is most often directed primarily at sampling, rather than completely removing, the targeted lesion, although the use of vacuum-assisted large core needles has made removal more achievable [16]. Imaging followup is recommended to ensure that lesions with benign pathologic results at needle biopsy retain benign imaging characteristics. The intention is to discover any false-negative lesions without significant delay. A number of reports in the literature include evaluation of the 6-month imaging follow-up examination after biopsy, but the results are inconsistent. In many reports, the imaging follow-up protocol is unclear or not well defined, or the compliance rate is low [17 20]. For example, Manjoros and colleagues [20] recommended 6-month imaging follow-up for all patients with benign needle biopsy results, but their compliance rate was only 54%. Achieving high compliance takes significant effort [21]. Our nursing staff contacts directly all patients who have undergone needle biopsy with their results and schedules the follow-up appointment at that time. A strength of our study is the uniform recommendation for benign concordant results and the high compliance rate (94.9%) with that recommendation. Many reports show few lesions that have changed early in the follow-up period, although the first attempt at imaging is neither consistently short nor uniform [5, 6, 8, 20, 22, 23]. A report by Salkowski and colleagues [8] found that 6- and 12-month follow-up imaging have equivalent rebiopsy rates, and those authors concluded that the 6-month follow-up examination is, therefore, unnecessary. However, they had no malignancies in either group, and their discordance rate (10.2%) was high. In addition, the recommendation for followup imaging was based on pathologic findings, with 6-month imaging follow-up used for nonspecific diagnoses and specific diag- AJR:207, October

5 Monticciolo et al. noses with atypical features, an approach that is somewhat variable. The decision to follow lesions according to pathologic findings was suggested by Lee and colleagues [6] on the basis of their analysis of 298 benign cases. Benign nonspecific diagnoses were believed to benefit from 6-month follow-up, whereas benign definitive diagnoses could wait 1 year. Our results suggest that reliance on pathologic findings for this determination is not useful. In our follow-up of 1444 cases, only 34 (2.4%) changed at imaging and there was no statistically significant difference between those with definitive pathologic findings (21 cases) or those with nonspecific pathologic results (13 cases; p = 0.60). In fact, the most common progressive lesion was a benign definitive one, fibroadenoma, which made up half of all lesions that changed. Five of these lesions were later diagnosed as benign phyllodes tumors, which are not false-negatives (not cancer) but need attention nonetheless. Although all would eventually be discovered at longer follow-up, an argument can be made for finding these lesions sooner, to limit the extent of surgery needed for treatment. Still, only five of 606 fibroadenomas (0.8%) had this outcome. One recent report looked at 6-month follow-up versus the recommendation to return to screening after biopsy by assessing population-based data from the Breast Cancer Surveillance Consortium [7]. Similar rates of cancer detection were found with the two follow-up recommendations. However, there are no data on needle size, sample number, clip placement, or postbiopsy imaging, because the report was not designed to capture these elements. In addition, those authors assumed that a biopsy within 90 days of the core needle procedure meant a discordant result, which is not always the case. They could not determine a spatial relationship between the finding that prompted the biopsy and the final cancer diagnosis. Although the findings are supportive of a return to routine imaging after needle biopsy, specific data on the lesions are lacking. False-negative rates for core needle breast biopsy have decreased over time [9, 17, 18, 21, 24]. In our report, the false-negative rate was low and yet was achieved by a lower number of cores than suggested in many literature reports [24 26]. This was particularly true of stereotactic-guided biopsy with vacuumassisted core needles. Our mean number of cores for stereotactic-guided biopsy was 4.6, far fewer than the 20 cores suggested in a European consensus report [26], but in line with others who have found 2 12 cores acceptable [4, 24]. Lomoschitz and colleagues [25] found that increasing the number of cores did not eliminate underdiagnosis. In our practice, we target mainly calcifications with stereotacticguided biopsy. After initial sampling of four or five cores, we image to see whether retrieval is adequate for diagnosis. If so, we limit additional sampling. This is an attempt to have less time on the table for the patient and fewer and smaller postbiopsy hematomas. Concordant results require calcifications in the specimen radiograph. Our diagnostic accuracy has been good, and we found no false-negatives over the 7-year study period. Our results suggest that a careful review of lesion targeting and lesion assessment for discordance could alleviate some falsenegative results. One of our false-negatives was discovered because of changes at the 6-month follow-up examination, but it was clearly discordant and undersampled at the time of biopsy. The other false-negative case was stable at short-interval follow-up (4 months) and was seen to have progressed only when the patient returned 17 months after follow-up. This delay could have been avoided by noting the lack of calcifications in the specimen radiograph, clearly required for targeting this type of lesion. This lesion should have been assessed as discordant. The short-interval follow-up was not helpful in this case. There are limitations to our study. Ninety cases (2.8%) were lost to follow-up, and an additional 261 (8.0%) patients returned but did not have long enough follow-up to be included in our analysis, which could have affected our results. Also, our rate of discordance was low, at 3.8% (124/3256 lesions). Although this is in keeping with the suggestion that discordance at image-guided biopsy is less than 6% [27], others have much higher rates, up to 12% [8, 28]. Lower discordance rates would suggest a greater dependence on follow-up imaging to reveal false-negative lesions, because some imagers may be willing to accept a marginal radiologic-pathologic correlation knowing that the patient will return in a few months. However, in spite of our low rate of discordance, our false-negative rate was very low. In our practice, we recommend 6-month follow-up imaging in all cases of benign concordant results, with a very high compliance rate. It is possible that this safety net has allowed us a lower discordance rate than could be translated to other practices. Overall, our evaluation of lesions with benign concordant biopsy results shows that selection of follow-up interval should not be dictated by whether pathologic findings are definitive or nonspecific. The number of lesions that progressed at imaging was low (2.4%), and the 6-month follow-up imaging benefited only a small number of patients. Although several benign phyllodes tumors were missed at initial needle biopsy, this made up only 0.8% of fibroadenoma diagnoses. 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