Background: Surgeons may receive a different diagnosis when a breast biopsy is interpreted by a second pathologist. The extent to which diagnostic agreement by the same pathologist varies at two time points is unknown. Methods: Pathologists from eight U.S. states independently interpreted 60 breast specimens, one glass slide per case, on two occasions separated by ≥9 months. Reproducibility was assessed by comparing interpretations between the two time points; associations between reproducibility (intraobserver agreement rates); and characteristics of pathologists and cases were determined and also compared with interobserver agreement of baseline interpretations. Results: Sixty-five percent of invited, responding pathologists were eligible and consented; 49 interpreted glass slides in both study phases, resulting in 2940 interpretations. Intraobserver agreement rates between the two phases were 92% [95% confidence interval (CI) 88–95] for invasive breast cancer, 84% (95% CI 81–87) for ductal carcinoma-in-situ, 53% (95% CI 47–59) for atypia, and 84% (95% CI 81–86) for benign without atypia. When comparing all study participants’ case interpretations at baseline, interobserver agreement rates were 89% (95% CI 84–92) for invasive cancer, 79% (95% CI 76–81) for ductal carcinoma-in-situ, 43% (95% CI 41–45) for atypia, and 77% (95% CI 74–79) for benign without atypia. Conclusions: Interpretive agreement between two time points by the same individual pathologist was low for atypia and was similar to observed rates of agreement for atypia between different pathologists. Physicians and patients should be aware of the diagnostic challenges associated with a breast biopsy diagnosis of atypia when considering treatment and surveillance decisions.
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