IMPORTANCE
A breast pathology diagnosis provides the basis for clinical treatment and management decisions; however, its accuracy is inadequately understood.
OBJECTIVES
To quantify the magnitude of diagnostic disagreement among pathologists compared with a consensus panel reference diagnosis and to evaluate associated patient and pathologist characteristics.
DESIGN, SETTING, AND PARTICIPANTS
Study of pathologists who interpret breast biopsies in clinical practices in 8 US states.
EXPOSURES
Participants independently interpreted slides between November 2011 and May 2014 from test sets of 60 breast biopsies (240 total cases, 1 slide per case), including 23 cases of invasive breast cancer, 73 ductal carcinoma in situ (DCIS), 72 with atypical hyperplasia (atypia), and 72 benign cases without atypia. Participants were blinded to the interpretations of other study pathologists and consensus panel members. Among the 3 consensus panel members, unanimous agreement of their independent diagnoses was 75%, and concordance with the consensus-derived reference diagnoses was 90.3%.
MAIN OUTCOMES AND MEASURES
The proportions of diagnoses overinterpreted and underinterpreted relative to the consensus-derived reference diagnoses were assessed.
RESULTS
Sixty-five percent of invited, responding pathologists were eligible and consented to participate. Of these, 91% (N = 115) completed the study, providing 6900 individual case diagnoses. Compared with the consensus-derived reference diagnosis, the overall concordance rate of diagnostic interpretations of participating pathologists was 75.3% (95% CI, 73.4%–77.0%; 5194 of 6900 interpretations).
Consensus ReferenceDiagnosis
Pathologist Interpretation vs Consensus-Derived Reference Diagnosis, % (95% CI)
No. ofInterpretations
Overall ConcordanceRate
OverinterpretationRate
UnderinterpretationRate
Benign without atypia
2070
87 (85–89)
13 (11–15)
Atypia
2070
48 (44–52)
17 (15–21)
35 (31–39)
DCIS
2097
84 (82–86)
3 (2–4)
13 (12–15)
Invasive carcinoma
663
96 (94–97)
4 (3–6)
Disagreement with the reference diagnosis was statistically significantly higher among biopsies from women with higher (n = 122) vs lower (n = 118) breast density on prior mammograms (overall concordance rate, 73% [95% CI, 71%–75%] for higher vs 77% [95% CI, 75%–80%] for lower, P < .001), and among pathologists who interpreted lower weekly case volumes (P < .001) or worked in smaller practices (P = .034) or nonacademic settings (P = .007).
CONCLUSIONS AND RELEVANCE
In this study of pathologists, in which diagnostic interpretation was based on a single breast biopsy slide, overall agreement between the individual pathologists’ interpretations and the expert consensus–derived reference diagnoses was 75.3%, with the highest level of concordance for invasive carcinoma and lower levels of concordance for DCIS and atypia. Further research is needed to understand the relationship of these findings with patient management.