“Suspicious” salivary gland FNA: risk of malignancy and interinstitutional variability

BACKGROUND: Fine-needle aspiration (FNA) cytology is well accepted as a safe, reliable, minimally invasive, and cost-effective method for the diagnosis of salivary gland lesions. Salivary gland neoplasms are often difficult to diagnose because of morphologic heterogeneity and a variety of epithelial metaplastic changes. Hence, a number of salivary gland FNA specimens yield indeterminate results. For indeterminate FNA specimens, the suspicious-for-malignancy (SFM) category is used when a specific neoplasm falls short in quantity or quality for the criteria for malignancy. Therefore, the findings are not sufficient for a conclusive diagnosis of malignancy. METHODS: This study was designed to evaluate the risk of malignancy (ROM) for the SFM group at 5 tertiary medical centers worldwide with the aforementioned criteria. Among 12,606 salivary gland FNA cases between 1997 and 2014, 276 (2.2%) were reported to be SFN. Specifically, 114 suspicious cases (41%) had histological follow-up. RESULTS: Histological follow-up of the 114 suspicious cases showed 95 malignant tumors indicating a risk of malignancy (ROM) of 83.3%. The ROM varied between 74% and 88% for the 5 participating institutions, and a Fisher's exact test with significance set to p<.05 showed no significant difference in ROM among the institutions (p =.78). CONCLUSIONS: Overall, 83.3% of SFM salivary gland FNA specimens turned out to be malignant; there was no significant interinstitutional variability in the ROMs. The SFM category for salivary gland FNA is very homogeneous, and the ROMs are quite similar worldwide