[582] Encapsulated Follicular Thyroid Tumor with Equivocal Nuclear Changes, So-Called Well Differentiated Tumor of Uncertain Malignant Potential, a Morphological, Immunohistochemical and Molecular Appraisal.

Zhiyan Liu, Yaqiong Li, Takashi Ozaki, Ichiro Mori, Emiko Taniguchi, Kennichi Kakudo. Wakayama Medical University, Japan

Background: Papillary thyroid carcinoma type nuclear changes (PTC-N) are the most reliable morphology in the diagnosis of PTC. However, there is a continuous debate regarding the classification of thyroid follicular lesions with equivocal PTC-N, and well differentiated tumor of uncertain malignant potential (WDT-UMP) was recently introduced by Williams to cover this problematic spectrum of thyroid tumors.
Design: A total of 30 cases of WDT-UMPs were examined. As a control, follicular adenoma (FTA, n = 16), follicular carcinoma (FTC, n = 8), hyalinizing trabecular adenoma (HTA, n = 5) and PTC (n = 48) were included. Immunohistochemical staining of HBME-1, cytokeratin 19 and galectin-3 were examined. BRAFV600E mutation and RET/PTC-1 rearrangement were investigated for all the WDT-UMPs.
Results: WDT-UMP had different nuclear features with the controls.

HBME-1, cytokeratin 19 and galectin-3 were positive in 12 (40%), 10 (33.3%) and 11 (36.7%) cases of WDT-UMP respectively.

According to the positivity of those markers, significant differences were obtained between WDT-UMP and PTC encapsulated common type (P = 0.030, 0.009 and 0.004), infiltrative follicular variant (P = 0.020, 0.008 and 0.026) and infiltrative common type (P = 0.022, 0.024 and 0.005) respectively, but no difference was demonstrated between WDT-UMP and FTA or FTC. Absence of BRAFV600E mutation but occurrence of RET/PTC1 rearrangement was found in 2 (6.7%) cases of WDT-UMP. None of the 20 patients with WDT-UMP developed recurrence with an average follow-up of 80 months.
Conclusions: These findings indicate that WDT-UMP has a favorable outcome and is distinct from PTC in morphological, immunohistochemical and molecular characteristics. We propose that WDT-UMP should be classified as 'well differentiated tumor with uncertain behavior'.
Category: Endocrine

Monday, February 28, 2011 9:30 AM

Poster Session I Stowell-Orbison/Surgical Pathology/Autopsy Awards Poster Session # 78, Monday Morning


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