In a recent editorial published in Cancer Cytopathology, Vol. 120:2, April 25, 2012, Dr. Michael Henry discusses the potential for overuse of atypical thyroid diagnoses according to The Bethesda System for Reporting Thyroid Cytopathology (TBSRTC). This journal also includes other articles related to thyroid FNA, interpretation and quality tools (to be discussed in a subsequent blog post). The articles included in this journal center around the AUS/FLUS categories, and suggestions for keeping these nebulous categories in check.
Just as the ASC:SIL ratio has been useful in cervicovaginal cytology, Dr. Henry describes the proposed use by Krane et. al of an AUS:Malignant (M) ratio as a quality tool to monitor the overcalling of AUS or undercalling of M. The authors suggest that this ratio should fall between 1.0 and 3.0 in most laboratories. In addition to following this ratio, the actual rate of AUS/FLUS cases, which TBSRTC recommends should not exceed 7%, is another metric to be monitored. Krane, et. al. reviewed data collected in 8 series of thyroid FNAs in institutions using TBSRTC, with a range of AUS/FLUS cases from 3.0% to 17.8%, and a combined rate of 9.7%. Bongiovanni et.al. discuss the role of molecular testing on AUS/FLUS cases, with cases with positive molecular markers having a high probability for a cancer outcome. However, they also suggest that currently available molecular markers "...are not as useful for the difficult thyroid FNA lesions...". Recently, "...microarray data from >200 genes have been used to produce a "benign thyroid fingerprint" that has the potential for use in guiding management of patients with an AUS/FLUS interpretation."
Dr. Henry discusses that
"...the objective of thyroid cancer diagnosis is not so much achieving a reduction in mortality as the prevention of morbidity."
And, as a result of the American Cancer Society's 2010 data indicating low mortality rates from thyroid cancer,
"...the goal of the cytopathologist in thyroid FNA should not necessarily be the elimination of all false-negative cases[,]...[but should be on] ways to improve the [quality] performance of their laboratories."
In summary, laboratories should establish a quality assessment program to monitor the results of their thyroid FNA program. This program would include monitoring of:
- overall diagnostic rates
- cyto-histo correlation and followup on surgically excised lesions
- rates of malignant outcomes according to FNA diagnostic categories and comparison with published benchmarks
- AUS:M ratio for overall laboratory and individual pathologists