Auxilio Mutuo Cancer, Hospital Auxilio Mutuo, San Juan, Puerto Rico
Received 16 June 2003; revised 13 October 2003; accepted 6 November 2003;
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ABSTRACT |
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Mammograms are assigned a BI-RADS (Breast Imaging Reporting and Data System) category, which indicates the level of suspicion for cancer.
Objectives:
(i) To evaluate the use of BI-RADS categories in a non-academic radiology practice based in a community hospital compared with local radiology private offices; (ii) to determine positive predictive value (PPV), sensitivity and specificity of mammograms; and (iii) to explore the correlation of BI-RAD 35 and lesion description with diagnosis of cancer.
Patients and methods:
We performed 947 SVABBs (stereotactic vacuum-assisted breast biopsies) on 911 patients with BI-RADS 35. Lesions were classified as: 1 = microcalcifications; 2 = asymmetric density; 3 = circumscribed mass; and 4 = spiculated mass.
Results:
BI-RADS category correlated with diagnosis of breast cancer (atypia excluded): category 3 = 4%; category 4 = 15%; and category 5 = 79%. The PPV of BI-RADS 4 and 5 for breast cancer or atypia was 20%, in contrast to 5% for BI-RADS 3. Sensitivity and specificity were 95% and 19%, respectively. For BI-RADS 3 without microcalcifications only 3% were positive, in contrast to 8% for remainder.
Conclusions:
First, there is a stepwise increase in cancer for each of the BI-RADS categories 35. Secondly, in BI-RADS 3 with microcalcifications, a biopsy is indicated according to our findings. Finally, the sensitivity of mammograms is 95% but the specificity is 19%.
Key words: biopsy, BI-RADS category, cancer diagnosis, mammography, SVABB
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Introduction |
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We decided to conduct this study with the following objectives: (i) to evaluate the use of BI-RADS categories in a non-academic radiology practice based in a community hospital as compared with the local radiology private offices; (ii) to determine if the use of BI-RADS categories 35 is useful and to explore whether the use of BI-RADS category 3 needs to be better defined; (iii) to determine the positive predictive value (PPV), sensitivity and specificity of mammograms; and (iv) to explore the correlation of BI-RAD 35 and description of lesion with the diagnosis of cancer.
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Materials and methods |
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Before the SVABB was performed, all patients were evaluated by one of three radiologists assigned to the Breast Imaging Section and all films were reviewed. A BI-RADS category was assigned before the SVABB. Either a surgeon or a radiologist performed the SVABB procedure. During this period of time, four surgeons and three radiologists performed SVABB. In order for a surgeon or a radiologist to perform this procedure he or she had to be credentialed by the Faculty By-Laws Committee. The criteria that were used for credentialization of surgeons are virtually identical to those proposed by the American College of Radiologists [3]. Whenever the surgeon performed the procedure, the radiologist assisted with the targeting. Before submitting the specimen to Pathology, it was first X-rayed in the Department of Radiology. Subsequently, all pathology reports were reviewed by the radiologist and an assessment of concordance or discordance was done on each case.
BI-RADS category was assigned using the interpretation provided by the first radiologist who read the films, either the outside radiologist or the institutional radiologist. Of the 947 mammograms done before the SVABB, 313 were performed at our center and 634 were performed outside. We identified 38 cases without microcalcifications in whom there was information on the exact size of the lesion. The median size was 0.9 cm (range 0.22.0 cm).
In order to calculate the specificity and sensitivity of the mammographic interpretation, we used the following formulae:
sensitivity = true-positive mammograms/true-positive mammograms plus false-negative mammograms
specificity = true-negative mammograms/false-positive mammograms plus true-negative mammograms
True-positive mammograms were defined as those with a BI-RADS >3 and a positive stereotactic biopsy for carcinoma or atypical hyperplasia. Those SVABBs considered to yield inadequate tissue that required a repeat biopsy with a resulting diagnosis of breast cancer or atypical hyperplasia were also considered as true positives, as well as anyone who upon follow-up required a repeat biopsy that was positive after the original SVABB.
A true-negative mammogram was defined as anyone with a BI-RADS category 3, with an initially negative stereotactic biopsy. Those with atypical hyperplasia were considered as positive and thus were not included as true negatives. Anyone requiring a repeat biopsy, which yielded a negative result, was also considered as a true negative. The tumor registry was also examined in an attempt to find any cases diagnosed as breast cancer whose initial SVABB was negative.
False-positive mammograms were defined as any BI-RADS >3 that yielded a negative result, including atypical hyperplasia, at the time of the first stereotactic biopsy or at rebiopsy for any reason, provided the repeat biopsy was negative. If upon follow-up a repeat biopsy had to be performed and it was positive then the case was considered a true-positive mammogram.
False-negative mammograms were defined as a BI-RADS 3 with a positive stereotactic biopsy result, including carcinoma or atypical hyperplasia. If a repeat biopsy in a BI-RADS 3 mammogram was performed and it was positive then the mammogram was also considered as a false negative; any initial biopsy in a BI-RADS 3 considered as inadequate tissue and requiring a repeat biopsy that was positive for breast cancer or atypical hyperplasia was also considered a false negative. Also those BI-RADS 3 who upon follow-up required a repeat biopsy that was positive were considered false negatives.
Permission was obtained from the local institutional review board for publication of the findings summarized in this study.
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Results |
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The three BI-RADS categories examined showed a stepwise correlation with the diagnosis of breast cancer (Table 1). Of the seven cancers diagnosed in BI-RADS category 3, one was LCIS (lobular carcinoma in situ), most likely an incidental finding, while six were DCIS (ductal carcinoma in situ).
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In order to compare our results in BI-RADS categories 35 with other published results using SVABB, we have summarized the available data in Table 2. There were no statistically significant differences when we compared our diagnostic yield on the first SVABB for the various BI-RADS categories with five published series, except for the fact that our 15% positive rate in category 4 was higher than in Berubes series, which had a rate of 4% (P <0.001), and also for category 5 where our positive rate was 79% compared with 54% (P = 0.005), respectively. Our positive rate was not statistically significantly different from those in the other four series.
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The specificity and sensitivity were also calculated classifying BI-RADS category 3 with microcalcifications as a positive mammogram (including also BI-RADS 4 and 5 as positive) and category 3 without microcalcifications as negative. Using this definition the sensitivity increased to 168 of 169 (99%), while the specificity dropped to 65 of 702 (9%). If category 3 mammograms with microcalcifications are considered positive, the positive predictive value of a mammogram would also drop to 159 of 881 (18%) from a level of 20% if only categories 4 and 5 are considered as positive mammograms.
With the goal of determining if there was any correlation between the description of the lesion observed in the mammogram and the result of the SVABB, we examined each of the major types of lesions, such as spiculated mass, circumscribed mass, microcalcifications and asymmetric density. The results are summarized in Table 3. The correlation between the mammographic features was not as good as with the BI-RADS category, except for the high frequency of cancer in cases with a spiculated mass. However, when BI-RADS category and type of mammographic lesion were combined, some useful patterns emerged (Table 4). Of the 90 cases of BI-RADS category 3 whose major lesion type was characterized by microcalcifications, six (7%) were diagnosed with cancer and another one with atypia (ADH), giving a total of seven of 90 (8%) positive findings in this subcategory. When BI-RADS category 3 cases without microcalcifications were examined separately, only two of 66 cases (3%) were found to have cancer while none had atypia. The only two cases of breast cancer within the BI-RADS category 3 without microcalcifications were a patient with an asymmetric density who had an invasive ductal carcinoma, and another with a circumscribed mass whose SVABB was initially negative but her follow-up mammogram 9 months later changed to a BI-RADS category 4. A biopsy was therefore performed and an invasive colloid carcinoma with an extensive in situ component was diagnosed.
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Table 5 shows in detail the types of breast cancers diagnosed in this study. The majority of cases (63%) were pure in situ carcinomas, mostly DCIS, followed by invasive carcinomas in 32%. Another 5% of the cases consisted of mixed invasive and in situ carcinomas. Table 6 shows the correlation between the type of mammographic lesion and the histological types of cancer diagnosed by SVABB. A total of 75% of the malignant lesions characterized by microcalcifications were associated with pure DCIS, while 39 of 45 (87%) of the other malignant lesions, including asymmetric densities, circumscribed masses and spiculated masses, were associated with invasive carcinomas. Of the 82 cases of DCIS, 79 (96%) were associated with microcalcifications, while 39 of 56 (70%) of the invasive carcinomas were associated with either a mass or an asymmetric density.
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Discussion |
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As expected with most screening tests, the sensitivity of mammography is excellent (95%) but the specificity is low (19%). This low specificity, however, is an underestimate because only cases with a BI-RADS category of 3 were biopsied. Those cases that fell into categories 1 and 2 were not biopsied and the likelihood that the vast majority of these were true negatives is higher than for category 3. If they were to be biopsied then the specificity of mammograms would most likely be considerably higher than in our study, which was limited to BI-RADS categories 35. Another factor that contributes to the relatively low specificity of stereotactic biopsy in our series is the small size of the tumors biopsied (median diameter 0.9 cm in cases where the lesion did not consist of microcalcifications).
Not surprisingly, 75% of the lesions characterized by microcalcifications were associated with pure DCIS and 87% of the other lesions, including asymmetric densities, circumscribed masses and spiculated masses, were associated with invasive carcinomas. Of the 82 cases of DCIS, 79 (96%) were associated with microcalcifications, while 39 of 56 (70%) of the invasive carcinomas were associated with either a mass or an asymmetric density.
In summary, the use of BI-RADS categories 35 appears to be effective in predicting the chances of finding either cancer or atypia. However, category 3 needs to be better defined, and subdividing it into categories 3-a and 3-b might be useful in terms of defining which patients in that category should be biopsied. Finally, caution is advised in extrapolating these findings to all cases where mammographic lesions are identified, because our study was limited to cases where the breast lesion was not palpable and not visualized by sonography. The results could be different for cases where the biopsy is obtained by sonography, because the frequency of masses rather than microcalcifications will be higher.
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FOOTNOTES |
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