A 4-Year Retrospective Analysis of Salivary Gland Cytopathology Using the Milan System for Reporting Salivary Gland Cytology and Ancillary Studies

Abstract

The cytopathology of salivary glands presents major challenges due to the heterogeneity of benign and malignant neoplasms, which is reflected in the large range of WHO 2017 Classifications. Fine needle aspiration (FNA) of salivary gland tumours is still the favoured initial approach as it results in good sensitivity and specificity. The Milan System for Reporting Salivary Gland Cytopathology (MSRSGC) was published in 2018 and comprises seven categories. We report results from a 4-year retrospective analysis of 328 salivary gland FNAs which were reviewed and classified according to the MSRSGC. We assess the risk of neoplasm, the risk of malignancy and the contribution of ancillary studies to the diagnosis. Benign neoplasms were the most frequent diagnosis (44.2%). Malignant and suspicious for malignancy were identified in 11.3% and 4.9% of diagnosed cases, respectively. Histopathological analysis after surgery was available for 216 (65.8%) of the cases. All malignant cases were confirmed post-surgery, and 68.8% of suspicious for malignancy were confirmed as malignant tumours. Immunocytochemistry was informative in 72.3% of cases. Immunocytochemistry and FISH provided the definitive diagnosis in 23.7% and 33% of cases, respectively. In conclusion, the MSRSGC is more effective when specific features of neoplasms can be identified. Ancillary studies help to further characterise salivary gland tumours and thereby increase the accuracy of MSRSGC.

The Milan system for reporting salivary gland cytopathology: The clinical impact so far. Considerations from theory to practice

“…The non‐diagnostic category carries a risk of malignancy (ROM) of 25%. The publication of papers analysing the role of the Milan System has further defined the ROM . In a recent study by Tommola et al, the non‐diagnostic category had a 0% ROM; however, a recent meta‐analytic study by Farahani analysed 92 studies including 16,456 SG‐FNA with surgical follow‐up The data from this study revealed a 7% ROM for the non‐diagnostic category based on 44 cases with histological follow‐up.…”

“…The series also supported the statement that the non‐diagnostic rate should be <10%. Nevertheless, the rate of non‐diagnostic FNA in the studies conducted at general hospitals was 21.28% ± 17.47% as compared to 4.38% ± 2.32% performed at referral or tertiary centres demonstrating an advantage for the latter group . The most common clinical management is represented by a repeat FNA with the use of ultrasound guidance and/or rapid on‐site evaluation in order to prevent a second non‐diagnostic result .…”

“…The current commentary describes the diagnostic categories of the Milan System and the main features of them. Furthermore, we provide data from the most recent salivary series adopting the Milan System for reporting their salivary cases …”

“…Non‐neoplastic lesions of the SGs are common and include benign entities such as reactive, metaplastic and inflammatory changes associated with acute or chronic inflammation, structural alterations or infection . The implied ROM for the non‐neoplastic category is approximately 10%, with studies ranging from 0% to over 20% . The Milan System Atlas offers a detailed description of this category including diagnostic criteria, photomicrographs and tables of a wide variety of non‐neoplastic entities such as sialolithiasis, acute, chronic and granulomatous sialoadenitis .…”

“…The ROM for AUS is approximately 20%. According to a recent meta‐analysis, only 16 out of 92 studies used the term atypia for a total of 110 cases respecting the strict criteria suggested by the Milan System . Moreover, the data assessed that the prevalence of histological benign entities (including non‐neoplastic and benign neoplasms) was 63% with a ROM at around 37% The introduction of the AUS category will probably be useful for certain specific entities such as predominantly cystic and mucin‐rich low‐grade mucoepidermoid carcinoma.…”