Should “atypical follicular cells” in thyroid fine‐needle aspirates be subclassified?

Abstract

BACKGROUND:Recently reported Bethesda terminology suggests the use of the term “atypical follicular cells” for thyroid fine‐needle aspirates. Previous work has suggested that some types of “atypical follicular cells” have different risks of malignancy.METHODS:The author reviewed the results of all thyroid aspirations with surgical resection performed during the past 13 years at our institution, subclassified the “atypical follicular cells,” and compared their relative risk of malignancy.RESULTS:During the 13 years in question, a total of 7089 cases were aspirated with 1331 resections. A total of 548 (14%) of all cases were classified as “atypical follicular cells,” and 204 (37%) were resected with an overall risk of malignancy of 25%. The risk of malignancy for atypical follicular cells subclassified as “rule out papillary carcinoma” was significantly higher (38%) than the other atypical cells. The risk of “rule out Hurthle cell neoplasm” was, at 7%, significantly lower than the other cases of atypical follicular cells (P<.001 and P<.02, respectively).CONCLUSIONS:Different types of “atypical follicular cells” have significantly different risks of malignancy. This disparity of risk should be communicated by the cytologist. Cancer (Cancer Cytopathol) 2010. © 2010 American Cancer Society.

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.…”