Rationale and Objectives
To increase radiologic knowledge, the distribution of mammographic features on prior screening mammograms of missed interval and screen-detected cancers was compared to the distribution on diagnostic mammograms of screen-detected cancers. The same variables were compared on mammograms of discordant and concordant screen-detected cancers.
Materials and Methods
The study was performed in Møre og Romsdal County, Norway, as a part of the quality assurance of the Norwegian Breast Cancer Screening Program. Women were screened using analog techniques and diagnosed from 2002 to 2008. Prior and diagnostic mammograms of 81 interval and 123 screen-detected breast cancers in women aged 50 to 71 years were retrospectively reviewed and classified as either missed or true by four experienced breast radiologists. Mammographic features were classified according to a modified Breast Imaging Reporting and Data System.
Results
Thirty percent (24 of 81) of the interval cancers and 21% (26 of 123) of the screen-detected cancers were classified as missed. Calcifications, alone or in association with mass or asymmetry, tended to be more common on prior mammograms of missed cancers compared to diagnostic mammograms of screen-detected cancers (34% [17 of 50] vs 21% [26 of 123], P = .114), whereas an opposite trend was seen for mass (54% [27 of 50] vs 68% [84 of 123], P = .109). Similar results were seen when comparing discordant and concordant cancers.
Conclusions
Calcifications represent a challenge in the interpretation of screening mammograms. For educational purposes, the importance of reviewing both interval and screen-detected cancers is obvious. Knowledge gained from systematic reviews might reduce the number of missed cancers on mammographic screening. Performing reviews according to established guidelines would make it possible to compare results across screening programs.
The term “interval cancer” refers to a breast cancer diagnosed in the interval between two screening sessions . Several studies have found that a substantial portion of interval cancers can be classified as missed on retrospective review. Thus, the interval cancer rate is considered a quality measure of a screening program. However, defining interval cancers is somewhat controversial , making comparisons of rates across screening programs difficult. The percentages of missed cancers have varied in previous studies because of different procedures for initial interpretation and review designs . In studies performed with prior screening mammograms and diagnostic mammograms available, roughly 20% to 30% of interval cancers showed signs on screening mammograms that, in a retrospective view, should have resulted in recall for diagnostic workup .
Despite the educational potential of reviewing mammograms of interval and screen-detected cancers in subsequently screened women, neither the European guidelines nor American recommendations describe preferable procedures for reviews or accepted levels for missed cancers . Actually, only a few studies have dealt with review of screen-detected cancers, despite the fact that the percentage of missed cancers seems to adhere to what is found in reviews of interval cancers .
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Materials and methods
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Study Population
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Retrospective Review Design
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Discordant Cancers
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Statistical Analyses
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Results
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Table 1
Interval and Screen-detected Breast Cancer Based on a Retrospective Review of Prior and Diagnostic Mammograms in Women Aged 50 to 71 Years
Classification Group Interval Cancer
(n = 81) Screen-detected Cancer ∗
(n = 123) All
(n = 204) Missed 18 (22.2%) 15 (12.2%) 33 (16.2%) Minimal signs actionable 6 (7.4%) 11 (8.9%) 17 (8.3%) Minimal signs not actionable 26 (32.1%) 46 (37.4%) 72 (35.3%) True 31 (38.3%) 51 (41.5%) 82 (40.2%)
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Table 2
Mammographic Features on Prior Mammograms of Missed Interval and Screen-detected Breast Cancer and on Diagnostic Mammograms of Screen-detected Breast Cancer in Women Aged 50 to 71 Years
Index Mammograms Diagnostic Mammograms Feature Missed Cancers
(n = 50) Screen-detected Cancers ∗
(n = 123) χ 2 P Value Mass 27 (54.0%) 84 (68.3%) .109 Calcification alone or in association with mass or asymmetry 17 (34.0%) 26 (21.1%) .114 Asymmetry 5 (10.0%) 2 (1.6%) .035 Architectural distortion 1 (2.0%) 8 (6.5%) .406 Occult 0 (0%) 3 (2.4%) .637
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Table 3
Shape, Margins, and Density of Mass ∗ Identified on Prior Mammograms of Missed Cancer and on Diagnostic Mammograms of Screen-detected Cancer in Women Aged 50 to 71 Years
Index Mammograms Diagnostic Mammograms Variable Missed Cancers
(n = 30) Screen-detected Cancers †
(n = 89) χ 2 P Value Shape Oval 2 (6.7%) 3 (3.4%) .801 Round 1 (3.3%) 11 (12.4%) .285 Irregular 26 (86.7%) 72 (80.9%) .660 Lobular 1 (3.3%) 3 (3.4%) 1 Margins Circumscribed 1 (3.3%) 1 (1.1%) 1 Indistinct 15 (50.0%) 31 (34.8%) .208 Spiculated 14 (46.7%) 57 (64.0%) .144 Density High 0 (0%) 5 (5.6%) .424 Isodense 30 (100%) 84 (94.4%) .424
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Table 4
Mammographic Features on Diagnostic Mammograms of Discordant and Concordant Screen-detected Breast Cancer ∗ in Women Aged 50 to 71 Years
Feature Discordant Cancer
(n = 30) Concordant Cancer
(n = 93) χ 2 P Value Mass 16 (53.3%) 68 (73.1%) .072 Calcification alone or in association with mass or asymmetry 9 (30.0%) 17 (18.3%) .267 Architectural distortion 4 (13.3%) 4 (4.3%) .187 Asymmetry 1 (3.3%) 1 (1.1%) .984 Occult 0 (0%) 3 (3.2%) .753
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Table 5
Shape, Margins, and Density of Mass ∗ Identified on Diagnostic Mammograms of Discordant and Concordant Screen-detected Breast Cancer † in Women Aged 50 to 71 Years
Variable Discordant Cancer
(n = 17) Concordant Cancer
(n = 72) χ 2 P Value Shape Oval 0 (0%) 3 (4.2%) .913 Round 3 (17.6%) 8 (11.1%) .744 Irregular 14 (82.4%) 58 (80.6%) 1 Lobular 0 (0%) 3 (4.2%) .913 Margins Circumscribed 0 (0%) 1 (1.4%) 1 Indistinct 9 (52.9%) 22 (30.6%) .144 Spiculated 8 (47.1%) 49 (68.1%) .180 Density High 0 (0%) 5 (6.9%) .594 Isodense 17 (100%) 67 (93.1%) .594
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Discussion
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Conclusions
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