The Milan system for reporting salivary gland cytopathology: A study of inter-observer reproducibility

In 2018, the Milan System for Reporting Salivary Gland Cytopathology was published defining a diagnostic categorization scheme with known malignancy risks and clinical follow up recommendations. Inter-observer reproducibility of the categories was not defined.

Salivary gland fine-needle aspirations (FNA) were reviewed over a 5 year period and classified by three independent observers. Inter-observer reproducibility was estimated using observed agreement and chance corrected agreement (Cohen's kappa).

Four hundred and eight cases were reviewed with chance corrected agreement of 0.42 for the original Milan System and 0.48 for a modified system using "similar follow up" categories. Categories 4A and 6B showed substantial agreement (kappa =0.71 and 0.72).

The Milan System shows moderate over all agreement between observers. Strongest inter-observer agreement was seen for categories 4A and 6B.