Interobserver Agreement for the International Academy of Cytology Yokohama System for Reporting Breast Fine-Needle Aspiration Biopsy Cytopathology

Background: A number of guidelines have been developed to improve standardization of the terminology and criteria for cytologic specimens obtained from the thyroid, pancreas, lung, and salivary glands. A major goal of these guidelines is to improve reproducibility and understanding of the reporting of diagnostic results among cytopathologists and between cytopathologists and clinicians. The International Academy of Cytology Yokohama System for Reporting Breast Fine-Needle Aspiration Biopsy Cytopathology (IAC YSRB) is the most recent of these guidelines. The value of this system is, in part, dependent upon interobserver reproducibility. Design: Ninety consecutive fine-needle aspiration biopsies (FNAB) of the breast, performed over a 6-year period, were independently evaluated by 4 board-certified pathologists blinded to the original diagnoses. The 5 diagnostic categories used were those of the IAC YSRB according to published criteria for these categories. Observed agreement and chance corrected agreement (Fliess κ) were calculated. Differences in κ values were evaluated using the T statistic of Gwent. Statistical calculations were performed using STATA v16.0 (STATA Corp., College Station, TX, USA). Results: Overall agreement between observers was good. Observed unweighted agreement was 69% and weighted agreement was 91%. The majority of diagnoses were concordant (68.6%). Conclusions: Interobserver agreement of 4 cytopathologists was good using the 5 categories of the IAC YRSB (69%). Agreement was greater among pathologists with more years of experience. The IAC YSRB system appears to provide greater agreement among viewers than guidelines for cytologic specimens obtained from some other body sites (salivary gland and lung). Most discrepancies were only by a single category, with only 22/113 (19%) differing by more than one category.