SUPPLEMENT 1 SPECIAL ISSUE: CYTOPATHOLOGY OF THE THYROID GLAND Guest Editor: Zubair Baloch Correlation of Thyroid Nodule Fine-Needle Aspiration Cytology With Corresponding Histology at Mayo Clinic, 2001–2007: An Institutional Experience of 1,945 Cases Justin L. Seningen, M.D., Aziza Nassar, M.D., * and Michael R. Henry , M.D. Following the National Cancer Institute Thyroid Fine Needle Aspi- ration State of the Science Conference, the thyroid fine-needle aspi- ration biopsy (FNAB) practice at Mayo Clinic, Rochester, Minne- sota, conducted retrospective analyses correlating cytologic and histologic evaluations of thyroid nodules. Cytologic and histologic reports were retrieved for patients with thyroid nodules who under- went thyroid FNAB between January 2001 and December 2007, with subsequent surgical thyroid resection. Cases were classified by major cytologic and histologic diagnosis and specific diagnostic subcategories. Of 1,945 FNAB cytologic results, 180 (9.3%) were nondiagnostic; 512 (26.3%) were negative for malignancy; 27 (1.4%) were atypical; 729 (37.5%) were suspicious for malignancy; and 497 (25.6%) were positive for malignancy. Histology was be- nign in 1,179 (60.6%) and malignant in 766 (39.4%). For thyroid malignancy as the disease outcome, at cytologic thresholds of atyp- ical, suspicious, and positive, overall sensitivity of thyroid FNAB was 94.5%, 94.1%, and 65.0%, respectively, and specificity was 46.0%, 48.3%, and 98.5%, respectively. Positive predictive value for all malignancies was 97.0%, and negative predictive value was 92.0%. When separated by specific malignant outcomes, diagnoses of papillary carcinoma, medullary carcinoma, and lymphoma had specificity of suspicious FNAB diagnoses ranging from 90.5% to 99.6%; positive predictive value ranged from 87.5% to 91.4%. For follicular or Hu¨rthle carcinoma, suspicious FNAB diagnoses had a specificity of 52.5% and a positive predictive value of 5.9%. Sensi- tivity of indeterminate FNAB diagnoses ranged from 72.7% to 95.3%. For follicular or Hu¨rthle pattern malignancies, indetermi- nate cytologic diagnoses should be interpreted with caution by the clinician considering surgical management. Diagn. Cytopathol. 2012;40:E27–E32. ' 2010 Wiley Periodicals, Inc. Key Words: correlation; cytology; fine-needle aspiration; his- tology; thyroid Thyroid nodules are quite prevalent in the US population, with palpable nodules occurring in 4–7% to nonpalpable nodules in 60% of the population. 1–6 Only about 5% of these nodules contain malignancy requiring surgical inter- vention. 1,5,7–9 Thyroid fine-needle aspiration biopsy (FNAB) has emerged as an efficient method for separating patients whose nodules can be managed by clinical surveillance from surgical candidates. 1–3,10–20 Moreover, although histol- ogy is the primary method for diagnosing thyroid carci- noma, 21 malignant thyroid lesions can often be specifically subcategorized on the basis of FNAB findings, thus provid- ing further predictive information to plan the patient’s course of care. 3,18 However, among institutions systematic classification in reporting thyroid FNAB results varies con- siderably. 1,13 Because the decision to pursue surgical man- agement is greatly influenced by the FNAB result, the need for consistency in the reporting and statistical evaluation of thyroid FNAB is essential to its clinical utility. 1,22 A major confounding factor in reporting cytology is the indeterminate category, which may comprise 6–55% of an institution’s thyroid FNAB reports. 1,13,23–27 Cytology that is neither clearly benign nor malignant shifts responsibility of determining a lesion’s importance onto the clinician and ultimately reduces the power of FNAB as a screening test. When considered as a positive test, indeterminate status increases the sensitivity of FNAB and reduces its specific- Mayo Clinic Foundation and Mayo Medical School, College of Medi- cine, Rochester, Minnesota *Correspondence to: Aziza Nassar, MD, Division of Anatomic Pathol- ogy, Mayo Clinic, 200 First St SW, Rochester, MN 55905. E-mail: nassar.aziza@mayo.edu Received 28 May 2010; Accepted 3 September 2010 DOI 10.1002/dc.21566 Published online 3 December 2010 in Wiley Online Library (wileyonlinelibrary.com). ' 2010 WILEY PERIODICALS, INC. Diagnostic Cytopathology, Vol 40, No S1 E27