[470] Atypia of Undetermined Significance in Thyroid Fine-Needle Aspirations: Prognostic Value of Architectural and Cytologic Atypia

PA VanderLaan, JF Krane. Brigham and Women's Hospital, Boston, MA

Background: The atypia of undetermined significance (AUS) diagnostic category as defined in the 2007 National Cancer Institute (NCI) Thyroid Fine Needle Aspiration (FNA) State of the Science Conference is a heterogeneous category between benign and suspicious for malignancy. The clinical behavior of these lesions as a group is not well defined, nor is there significant data as to subgroup characteristics that may impart a higher risk of malignancy. Here, we report the prognostic significance of specific diagnostic features of AUS FNAs.
Design: All thyroid FNAs performed at Brigham and Women's Hospital from 1/05 to 4/09 with a diagnosis of AUS were analyzed retrospectively. As appropriate, our laboratory qualifies AUS as being due to cytologic or architectural atypia (or both). Follow-up data from repeat FNA or surgical resection were correlated with AUS qualifiers as well as any other diagnostic descriptors provided in the original report (atypia severity, specimen cellularity, number of atypical cells, presence of colloid, histiocytes, cyst lining cells, or Hurthle cell changes).
Results: A total of 306 thyroid AUS FNAs had conclusive follow-up data, stratified on the basis of atypia (see table). The risk of malignancy for architectural atypia alone (14%) was significantly lower than that observed for the other groups (Z=2.282, >95% CI): cytologic atypia (30%), both cytologic and architectural atypia (28%), or unspecified atypia (32%). No significant predictive value was noted for any of the other descriptive qualifiers, either with respect to AUS lesions overall or for any of the four atypia subcategories.

Outcome for thyroid AUS FNAs based on atypia qualifier

	Architectural	Cytologic	Both	Unspecified	Total
Benign	55 (86%)	38 (70%)	58 (72%)	73 (68%)	224 (73%)
Malignant	9 (14%)	16 (30%)	22 (28%)	35 (32%)	82 (27%)
Total	64 (21%)	54 (18%)	80 (26%)	108 (35%)	306

Conclusions: As a group, 27% of thyroid FNAs diagnosed as AUS with clinical follow-up are malignant. Our data indicate that the isolated presence of architectural atypia has approximately half the relative risk for malignancy compared to AUS with cytologic atypia, cytologic as well as architectural atypia, or with no further descriptor provided. Apart from these atypia qualifiers, no other diagnostic features were noted to carry significant prognostic weight in interpreting AUS FNAs, although case numbers were limited for many of these qualifiers. Further study is needed to establish whether distinct patterns of AUS warrant different clinical follow-up algorithms.
Category: Cytopathology

Tuesday, March 23, 2010 9:30 AM

Poster Session III # 89, Tuesday Morning