Subtyping salivary gland neoplasm of uncertain malignant potential based on cell type demonstrates differential risk of malignancy

Abstract

BACKGROUND The newly unveiled Milan System for Reporting Salivary Gland Cytopathology (MSRSGC) has proposed salivary gland neoplasm of uncertain malignant potential (SUMP) as an indeterminate category. The category is reserved for fine‐needle aspiration (FNA) cases that are diagnostic of a salivary gland neoplasm but cannot be further designated as a specific tumor type. The objective of the current study was to evaluate the clinical utility of subtyping SUMP cases based on different cell types. METHODS A retrospective search of cytology databases at 2 institutions for salivary gland FNAs from 2006 through 2017 was conducted. The cytologic diagnosis of each case was reclassified according to the MSRSGC. Histologic follow‐up was retrieved for correlation. Cases reclassified as SUMP that had a follow‐up pathologic diagnosis were subject to cytology review and subtyping into oncocytic/squamoid, basaloid, or myoepithelial subtypes based on cytomorphology. The risk of malignancy (ROM) for each subtype was analyzed. RESULTS There were 92 SUMP cases, which comprised 5.9% of 1560 consecutive salivary gland FNAs within the 12‐year study period. Histologic follow‐up was available for 59 patients. After cytology review, there were 18 cases (30.5%) of oncocytic/squamoid subtype, 25 (42.4%) of basaloid subtype, and 16 (27.1%) of myoepithelial subtype. Pathologic correlation revealed an ROM of 61.1% (11 of 18 cases) for the oncocytic/squamoid subtype, 40.0% (10 of 25 cases) for the basaloid subtype, and 18.8% (3 of 16 cases) for the myoepithelial subtype. The differences in ROM among the 3 subtypes were statistically significant (P = .0476). CONCLUSIONS Subtyping SUMP cases into categories based on cell type demonstrated differential ROMs for better clinical stratification. Future prospective studies are mandatory to confirm this finding.

Cytohistologic correlation of basaloid salivary gland neoplasms: Can cytomorphologic classification be used to diagnose and grade these tumors?

“…SUMP used in conjunction with a pattern‐based system may further refine the differential diagnosis, clarify which SUMP neoplasms show a greater ROM, and improve clinicians' understanding of MSRSGC in a clinically meaningful way. One study found statistically significant differences in the ROM among SUMP cases when they were subtyped as having an oncocytic/squamoid (61.1%), basaloid (40.0%), or myoepithelial morphology (18.8%) . In our cohort of basaloid SUMP cases, the ROM was 22%, which was much lower than that in the study by Hang et al In the pattern‐based risk‐stratification scheme, Griffith et al found that the category of basaloid neoplasm with nonfibrillary stroma had a much higher ROM (68.8%) than the category of basaloid neoplasm with fibrillary stroma.…”

“…One study found statistically significant differences in the ROM among SUMP cases when they were subtyped as having an oncocytic/squamoid (61.1%), basaloid (40.0%), or myoepithelial morphology (18.8%) . In our cohort of basaloid SUMP cases, the ROM was 22%, which was much lower than that in the study by Hang et al In the pattern‐based risk‐stratification scheme, Griffith et al found that the category of basaloid neoplasm with nonfibrillary stroma had a much higher ROM (68.8%) than the category of basaloid neoplasm with fibrillary stroma. The findings of this study also support the importance of stromal character in that the ROMs of SUMP cases with fibrillary/chondromyxoid, hyaline, and absent stroma were 5.3%, 26.1%, and 37.5%, respectively.…”

Application of the Milan System for Reporting Salivary Gland Cytopathology: A retrospective study in a tertiary institute

“…Although this was lower than 35%, the value proposed by the MSRSGC, it was similar to the results in our study. Hang et al subclassified the neoplasms into basaloid, oncocytic/squamoid, and myoepithelial subtypes. The definition of the myoepithelial subtype does not correspond to the definition of the clear‐cell subcategory proposed by MSRSGC, which includes both the cytologic findings of classic pleomorphic adenoma with focal cellular atypia and those of tumors with predominantly myoepithelial cells.…”

The Milan system for reporting salivary gland cytopathology: A comprehensive review of the literature

“…In addition, the uniform terminology allows cross communication between pathologists and institutions. Since the print publication of the MSRSGC in 2018, many institutions across the world retrospectively applied this tired diagnostic scheme to their institutional cohort of cases or those collected from multiple institutions and reported their findings with and without surgical follow‐up 6‐43 …”