A multi‐institutional study of salivary gland cytopathology: Application of the Milan System for Reporting Salivary Gland Cytopathology in Japan

Abstract

BACKGROUND:The Milan System for Reporting Salivary Gland Cytopathology (MSRSGC) is a risk-stratification reporting system that was introduced in 2018. The objective of this multi-institutional study was to evaluate the utility of the MSRSGC in Japan. METHODS: In total, 1608 fine-needle aspiration samples with matching histologic diagnoses were retrieved from 12 large institutions in Japan. The diagnostic categories of the MSRSGC were assigned prospectively or retrospectively, and the results were compared with the histologic diagnoses. RESULTS: The cases were classified as follows: nondiagnostic, 18.1%; non-neoplastic, 4.1%; atypia of undetermined significance, 11.5%; neoplasm-benign, 43.7%; salivary gland neoplasm of uncertain malignant potential, 9.6%; suspicious for malignancy, 3.6%; and malignant, 9.4%. The risk of neoplasm and the risk of malignancy in each MSRSGC category were as follows: nondiagnostic, 72.9% and 13.4%, respectively; non-neoplastic, 15.2% and 9.1%, respectively; atypia of undetermined significance, 77.9% and 24.9%, respectively; neoplasm-benign, 99% and 1.8%, respectively; salivary gland neoplasm of uncertain malignant potential, 94.8% and 37%, respectively; suspicious for malignancy, 100% and 89.7%, respectively; and malignant, 100% and 99.3%, respectively. The accuracy of the MSRSGC for diagnosing neoplasms was 97.8%, and its accuracy for diagnosing malignancy was 97.3%. Institutions that used Romanowsky-stained preparations had lower nondiagnostic rates and lower risks of neoplasm and malignancy in the non-neoplastic category. CONCLUSIONS:The MSRSGC is useful for risk stratification and quality control. Widespread use of the MSRSGC would improve the accuracy of salivary gland cytology and lead to better patient care in Japan. Cancer Cytopathol 2021;0:1-11.

Multi‐institutional validation of a modified scheme for subcategorizing salivary gland neoplasm of uncertain malignant potential (SUMP)

“…Only SUMP cases with available glass slides for review and subsequent surgical resection were included. Among the 9938 salivary gland FNAs, 742 cases (7.4%) were classified as SUMP, which is comparable to the diagnostic rate reported in other large studies 13‐18 . Of these 742 cases, 329 (62.7%) had glass slides available for cytology review and surgical follow‐up.…”

“…Among the 9938 salivary gland FNAs, 742 cases (7.4%) were classified as SUMP, which is comparable to the diagnostic rate reported in other large studies. [13][14][15][16][17][18] Of these 742 cases, 329 (62.7%) had glass slides available for cytology review and surgical follow-up. The overall ROM for SUMP was 40.4%, higher than the estimation of 35% by the MSRSGC, but within the range of 39.4% and 42% reported in recent comprehensive and systematic reviews of the literature.…”

Nondiagnostic salivary gland FNAs are associated with decreased risk of malignancy compared with “all‐comer” patients: Analysis of the Milan System for Reporting Salivary Gland Cytopathology with a focus on Milan I: Nondiagnostic

“…Literature review yielded 50 studies that reported FROMs using MSRSGC (Table 3). 8,15–58 The FROM for ND FNAs was 15.7% ( n = 208/1320), which was significantly lower than the 24.9% ( n = 2645/10611) FROM for all‐comers ( p < .001). There were 32 studies that also included the overall numbers of FNA for each category.…”

Nondiagnostic category of Milan System for Reporting Pediatric Salivary Gland Cytopathology: outcomes and root cause analysis

“…In contrast to this low malignancy risk, MSRSGC estimates the general ROM in nondiagnostic aspirates to be approximately 25% and recommends repeat FNA, imaging studies such as contrast‐enhanced CT/MRI, alternative biopsy approaches, or surgery 18 . Recent studies with large number of cases reporting on the application of MSRSGC have shown variable ROMs for the nondiagnostic category, ranging from 0% to 20% 17,19,21‐27 . These case series, together with 2 minimally overlapping meta‐analyses, 17,21 are summarized in Table 6.…”

“…18 Recent studies with large number of cases reporting on the application of MSRSGC have shown variable ROMs for the nondiagnostic category, ranging from 0% to 20%. 17,19,[21][22][23][24][25][26][27] These case series, together with 2 minimally overlapping meta-analyses, 17,21 are summarized in Table 6. Only studies that incorporated at least 300 total FNAs with at least 100 histologic follow-up were included in this summary.…”