Objective: Oncocytic cells are commonly detected on FNA reports but little is known regarding the relationship between the degree of oncocytic cell features and the rate of malignancy (ROM). In this study, we aimed to investigate the importance of oncocytic cells in thyroid FNA with a diagnosis of atypia of undetermined significance (AUS). Additionally, we sought to ascertain if the prevalence of oncocytic cells in FNAs with oncocytic cells is linked to neoplasm and malignancy.

Material and Methods: 187 cases belonging to 144 patients diagnosed with AUS in thyroid FNA were re-evaluated for the oncocytic cells, nuclear atypia and microfollicles and then classified as AUS-nuclear with or without oncocytic cells and AUS-other with or without oncocytic cells. The cases that had oncocytic cells were scored according to the proportion of oncocytic cells.

Results: ROM was higher in the AUS-nuclear group (28.1%) compared to the AUS-other group (12.2%). AUS-nuclear cases without oncocytic cells had higher ROM compared to the AUS-nuclear cases with oncocytic cells. Rate of neoplasm (RON) was significantly higher in the cases containing 75% or more oncocytic cells than the other cases (p<0.0001). (26.3% for cases with 1–75% oncocytic cells, 81.3% for those with 75% or more oncocytic cells).

Conclusion: This study showed that the AUS cases with a dominant oncocytic cell population might be more specific for neoplastic processes. Presence of oncocytic cells in the AUS-nuclear cases causes a decrease in ROM. Emphasizing oncocytic cells in the report may contribute to patient follow-up and treatment in AUS.