Application of the Milan system for reporting salivary gland cytopathology using cell blocks

The Milan system for reporting salivary gland cytopathology (MSRSGC) is a novel standardized classification tool for salivary gland cytology specimens based on the use of direct smears. Formalin-fixed paraffin-embedded (FFPE) cell blocks facilitate the use of ancillary studies, leading to improved diagnostic accuracy. However, the application of the MSRSGC with only cell blocks has not been well established. Consecutive cohort of all parotid gland cytology specimens between 01/01/2018 and 30/06/2021 was performed. All cytology specimens were processed into cell blocks only. Cytologic diagnoses were classified prospectively according to the MSRSGC categories. The risk of malignancy (ROM) for each diagnostic category and the diagnostic performance were calculated. A total of 230 FNA samples from 221 patients were identified, including 47% and 78.4% with surgical or clinical follow-up, respectively. The ROMs based on surgical follow-up for the non-diagnostic, non-neoplastic, AUS, neoplasm: benign, SUMP, SFM and malignant categories were 21.4%,0%,50%,0%,30%,100% and 100%, respectively. The ROMs based on the clinical follow-up for these categories were 7.3%,0%,37.3%,0%,27.3%,100% and 100%, respectively. Following surgical excision, all Milan IVa category samples were confirmed as benign, and all Milan V and VI category samples were confirmed as malignant. This study validates the application of the MSRSGC with the sole use of FFPE cell blocks. The diagnostic accuracy of MSRSGC is high and compares favorably to other institutions using traditional cytology assessment methods. Furthermore, FNA results using this technique enabled to provide optimal patient management based on the ROM of the different Milan system categories.