[401] Cytopathologic Characteristics of Papillary Thyroid Carcinoma with RET/PTC Rearrangement

M Dvorakova, YE Nikiforov, MN Nikiforova, KE Schoedel, NP Ohori. University of Pittsburgh Medical Center-Presbyterian, Pittsburgh, PA

Background: RET/PTC gene rearrangement is found in a significant number of sporadic papillary carcinoma (PTC). RET/PTC rearranged PTC typically show classic PTC histology and present in younger patients with lymph node metastasis. With incorporation of molecular testing as an adjunct to thyroid fine needle aspiration (FNA) diagnosis, RET/PTC rearranged PTC is detected in cytology cases. In this study, we evaluated the cytopathologic parameters of RET/PTC rearranged PTC.
Design: Cytology specimens of histologically proven PTC were selected from the cytology files dating from April 2007 to June 2009. At the time of the FNA, cytology samples were collected for direct smears, thin-layer processing, and molecular studies. The material for the molecular studies was collected directly into nucleic acid preservative solution and RT-PCR was performed to amplify the fusion points of RET/PTC1 and RET/PTC3. The cytology diagnoses were categorized according to the Bethesda system and were made independently of the molecular results. For each case, the original cytology diagnoses and the cytologic features (in particular, the number of intranuclear pseudoinclusions (IPI) in the most diagnostic area of 50 cells) were evaluated. The group of RET/PTC rearranged PTC was compared to a control group of RET/PTC negative cytology cases with histologically proven PTC in the resection specimen.
Results: Seven (7) cases of histologically proven PTC cases with RET/PTC rearrangement were identified. All seven cases were diagnosed as PTC cytologically and demonstrated an average of 3.2 IPI in the most diagnostic area. In contrast, only 1 of 8 cases of histologically proven PTC without genetic alteration were diagnosed as PTC on cytology and demonstrated an average of 1.0 IPI in the most diagnostic area. The differences in the 2 groups regarding the original diagnosis (p=0.001, Fisher's exact test) and IPI (p=0.004, T-test, parametric) were statistically significant.
Conclusions: Cytology specimens of PTC with RET/PTC rearrangement demonstrate an increased number of IPI and are associated with a larger proportion of cases diagnosed as PTC by cytomorphology alone when compared to PTC cases without this genetic alteration.
Category: Cytopathology

Tuesday, March 23, 2010 9:30 AM

Poster Session III # 98, Tuesday Morning

 

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