[583] PAX8/PPARγ Rearrangements of Thyroid Tumors: Assessment of Distribution Frequency, Histopathological Features and Cytological-Histopathological Correlations

Huaitao Yang, Michaele Armstrong, Sally Carty, Paul Ohori, Yuri Nikiforov. University of Pittsburgh, Pittsburgh, PA

Background: PAX8/PPARγ rearrangements have been found in follicular thyroid carcinoma (FTC), follicular variant papillary thyroid carcinoma (FVPTC), and follicular adenoma. However, large-scale data have not been reported regarding its prevalence, cytological-histopathological correlation, and histopathological features. We reported the retrospective findings of thyroid tumors for positive PAX8/PPARγ rearrangements.
Design: We reviewed all cases for PAX8/PPARγ rearrangement of at our institution in the interval of 2007 to 2012. Its distribution frequency, histopathological features and cytological-histopathological correlations were assessed. Tumor size, vascular and capsular invasion, resection margins, extra-thyroid extension, encapsulation, thickness of capsule, solid growth, metastatic status of regional lymph nodes was also recorded.
Results: During a 6-year period of 2007-2012, 16 cases of PAX8/PPARγ rearrangement were identified. In cytology FNA aspirations, this rearrangement was found in 9 (64.3%) follicular lesion/neoplasm (FNL), 2 (14.3%) oncocytic (Hürthle cell) lesion/neoplasm (OHNL), 2 (14.3%) FLUS, 1 (7.1%) negative. 14 PAX8-PPARγ rearrangement-positive thyroid cancers included 9 FVPTC (64.3%), 3 FTC (21.4%), 2 PTC solid variant (14.3%). Among 9 FVPTC, the cytology FNA diagnosis were 5 FNL, 1 OHNL, 1 FLUS, 1 negative and 1 not-done. Two of 3 FTC were FNL. All 2 PTC solid variant were FNL. Average tumor size of TFC, FVPTC and PTC solid variant was 3.4, 3.7, 4.0 cm respectively. Variable solid growth pattern was present in both FTC (0-40%) and FVPTC (0-30%). All 3 FTC, 9 FVPTC and 2 PTC solid variant were encapsulated and none of them showed extrathyroid extension, positive lymph nodes and positive margins. Vascular invasion of FTC, FVPTC, PTC solid variant was 66% (2/3), 33% (3/9), 50% (1/2) respectively. The capsular invasion of them was 100% (3/3), 56% (5/9) and 50% (1/2) respectively.
Conclusions: Our data indicated that: 1) Most thyroid tumors with PAX8/PPARγ rearrangement are encapsulated FVPTC, followed by FC and PTC solid variant; 2) PAX8/PPARγ was not present in other subtypes such as infiltrative/nonencapsulated FVPTC; 3) PAX8/PPARγ-positive encapsulated FVPTC had features of high frequency of capsular invasion, vascular invasion, thick capsule, presence of variable solid growth, and absence of LN and extrathyroid extension.
Category: Endocrine

Monday, March 4, 2013 1:30 PM

Proffered Papers: Section H, Monday Afternoon


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