Comparative analysis of the World Health Organization Reporting System for Head and Neck Cytopathology and the Milan System for Reporting Salivary Gland Cytopathology

Background A comparative analysis of the International Academy of Cytology–International Agency for Research on Cancer–World Health Organization Reporting System for Head and Neck Cytopathology (WHO) and the Milan System for Reporting Salivary Gland Cytopathology (MSRSGC) was performed. Methods A total of 2218 salivary gland fine‐needle aspiration samples collected at the Institut Curie, Paris (1954–2022) were evaluated, with 1356 having histological follow‐up. Samples were classified according to the MSRSGC (nondiagnostic [ND], nonneoplastic [NN], atypia of undetermined significance [AUS], benign neoplasm [BN], salivary gland neoplasm of uncertain malignant potential [SUMP], suspicious for malignancy [SM], and malignant [M]) and the WHO system (insufficient/inadequate/nondiagnostic, benign, atypical, neoplasm of uncertain malignant potential [NUMP], suspicious for malignancy [SM], and malignant [M]). The risk of malignancy (ROM) was calculated for each category, and diagnostic performance metrics were assessed. Results In the MSRSGC, the ROM was ND, 50% ( n = 2); NN, 16.8% ( n = 149); AUS (no cases); BN, 4.3% ( n = 514); SUMP, 50% ( n = 2); SM, 56.1% ( n = 66); and M, 98.2% ( n = 623). In the WHO system, the ROM was insufficient/inadequate/nondiagnostic, 50% ( n = 2); benign, 7.1% ( n = 663); atypical (no cases); NUMP, 50% ( n = 2); SM, 56.1% ( n = 66); and M, 98.2% ( n = 623). The WHO’s “benign” category, which combines NN and BN, balanced the NN’s higher ROM (16.8%) and BN’s lower ROM (4.3%) into 7.1%. Excluding the ND and SUMP/NUMP categories, both systems demonstrated high diagnostic performance: sensitivity, 93.3%; specificity, 93.9%; positive predictive value, 94.2%; and negative predictive value, 92.9%. Conclusions Both systems effectively identify malignancy. The WHO system’s merger of NN and BN into the benign category streamlines reporting and reduces variability, although it may mask clinically significant differences between nonneoplastic and benign neoplastic lesions.