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Introduction: Fine-needle aspiration cytology (FNAC) is an effective tool in the diagnostic work-up of patients with thyroid nodules. The aim of our study was to assess the diagnostic sensitivity of FNAC in thyroid cancer (TC) in Sweden by correlating the findings of preoperative FNAC with those obtained through final histology of the surgical specimen.

Methods: A Swedish nationwide cohort of patients having surgery for TC (n = 2519) from the Scandinavian Quality Register for Thyroid, Parathyroid and Adrenal surgery between 2004 and 2013 was obtained. Data was validated through scrutinizing patient FNAC and histology reports.

Results: Among the 2519 cases operated with a final diagnosis of TC, the diagnosis was substantiated and validated through the histology report in 2332 cases (92.6%), included in the present study. Among these, 1679 patients (72%) were female and the median age at TC diagnosis was 52.3 years (range 18-94.6). In 353 cases (15.1%) FNAC was not performed at all; whereas in the remaining 1965 cases, the diagnostic sensitivity of FNAC was 81.6%. In lesions > 1 cm, FNAC diagnostic sensitivity reached 86.5%, whereas in lesions < 1 cm, FNAC yielded a sensitivity of 61.5%. Approximately 85% of FNACs (n = 1981/2332) were performed using ultra-sonographic (US) guidance. In TC lesions > 1 cm, the diagnostic sensitivity of US-guided FNAC (n = 1504) was 86.9% as compared to 76.9% in clinically applied FNAC without US utilization (n = 118).

Conclusions: FNAC is performed in most patients operated for TC in Sweden (85%) and retains its value as a tool in TC diagnostic work-up with an overall sensitivity of 82%, reaching 87% in lesions > 1 cm, that harbor clinically relevant TC.