Evidence‐based evaluation of the risks of malignancy predicted by thyroid fine‐needle aspiration biopsies

Abstract

A National Cancer Institute (NCI) "Thyroid Fine-Needle Aspiration (FNA) State of the Science Conference" recently proposed standardized nomenclature and "risks of malignancies" associated with various diagnostic categories. We evaluated the evidence levels of the data used by NCI to predict malignancy risks and whether those estimates had clinical validity in our patient population.Eight hundred seventy-nine patients underwent thyroid FNA during 2006. FNA diagnoses were translated into NCI diagnostic categories, and 2-year follow-up retrospective information was obtained. Four percentages of malignancies were calculated for each diagnostic category using follow-up information from FNA, thyroidectomy, both, and all patients as denominators. 95% confidence intervals (CI) were estimated for all proportions, and results were analyzed with chi-square statistics. "Relative risk" calculations were performed using the percentage of malignancies in the entire population under study as a denominator.Most of the studies cited by the NCI provided incomplete and variable level III evidence based mainly on surgical follow-up. Among our patients, the percentages of malignancies calculated with follow-up data from all patients as the denominator were similar to the "risk estimates" proposed by the NCI, but estimates based on surgical follow-up overestimated the probability of thyroid malignancy for patients with FNA diagnosis of "benign" and "follicular lesions of undetermined significance" (FLUS). Relative risk and 95% CI calculations suggested that the NCI classification could be simplified into three categories: "benign," "FLUS + neoplasm," and "suspicious + malignant."

The atypia of undetermined significance/follicular lesion of undetermined significance:malignant ratio

“…5,6,8,9,[12][13][14] The data from these series are summarized in Table 1. It is interesting to note that the overall rate of AUS was 9.7% with only 2 of 8 series reporting AUS rates below the previously recommended threshold of 7%.…”

“…In fact, most initial experiences with AUS have reported AUS rates > 7%, often substantially so. 3,[6][7][8][9][10][11][12]14 Our goal in undertaking this study was to identify performance measures within TBS that would guide reasonable laboratory practice, particularly with regard to use of the AUS category. We sought to establish whether a performance measure similar to the ASCUS:SIL ratio in cervical/vaginal cytology might be identifiable within thyroid FNA, although clearly recognizing that such a parameter will have limitations much as the ASCUS:SIL ratio does.…”

“…We identified PubMed-indexed, peer-reviewed published laboratory experiences using TBS in which the categorical breakdown of all 6 reporting tiers was identified 5,6,8,9,[12][13][14] and supplemented those data with previously unpublished figures from the Massachusetts General Hospital compiled by one of the authors (W.C.F.) from 2006 to 2008 using TBS (a subset of these cases was included in a prior study 3 ).…”

“…The heterogeneity of this low-risk category inevitably means that there will be differences in its utilization with significant variability in AUS rates noted among individual practitioners as well as between laboratories. [2][3][4][5][6][7][8][9][10][11][12][13][14] Indeed, TBS only recommends a broad use range for each diagnostic category. 1 To promote uniform practice among laboratories and cytopathologists and encourage quality improvement, it is desirable to have performance measures associated with TBS, especially with regard to the AUS category.…”

“…15 The only such recommendation that accompanied TBS for thyroid cytopathology was that the AUS rate not exceed 7% 1 ; however, this proposal lacked a robust evidentiary basis and has proved to be unrealistic for many laboratories publishing their initial experiences with TBS. [2][3][4][5][6][7][8][9][10][11][12][13][14] In this study, we review the initial published experiences with AUS and TBS in conjunction with our own laboratory experiences, with the goal of identifying evidencebased performance measures that will have usefulness in measuring individual and laboratory practices. In so doing, we hope to provide a basis for quality improvement in the reporting of thyroid aspirates within TBS framework.…”