[525] Immunohistochemical and Molecular Characteristics of Follicular Patterned Thyroid Nodules with Incomplete Papillary Thyroid Carcinoma-Like Nuclei

HS Min, G Choe, NY Cho, GH Kang, SH Park, SY Park. National Cancer Center, Goyang, Republic of Korea; Seoul National University Bundang Hospital, Seongnam, Republic of Korea; Seoul National University College of Medicine, Seoul, Republic of Korea

Background: Follicular patterned thyroid nodules with incomplete papillary thyroid carcinoma (PTC)-like nuclei (FTN-IPTCNs) are difficult to diagnose, and are often designated well-differentiated tumors of uncertain malignant potential in encapsulated follicular lesions. They are characterized by well-formed follicles with atypical nuclei mimicking those of PTC, but the extent of atypia is incomplete for definite diagnosis of PTC. Their biological behavior and association with follicular variants of PTC (FVPTC) have not yet been established.
Design: We investigated immunohistochemical features (galectin-3, HBME-1, CK19, fibronectin-1, CITED1), BRAF V600E mutation and RASSF1A promoter methylation status in 30 FTN-IPTCN cases, along with 26 FVPTCs, 21 follicular adenomas (FAs) and 14 nodular hyperplasias (NHs).
Results: Expression of galectin-3, HBME-1, CK19 and CITED1 was significantly higher in FTN-IPTCNs than in FAs or NHs, but expression of galectin-3, CK19 and fibronectin-1 was lower in FTN-IPTCNs than in FVPTCs. The BRAF V600E mutation was not detected in the benign nodules or FTN-IPTCNs, whereas 57% of FVPTCs had the mutation. RASSF1A promoter methylation was higher in FTN-IPTCNs than in benign nodules but there was no difference between FTN-IPTCNs and FVPTCs.
Conclusions: We conclude that FTN-IPTCN is an intermediate lesion between a benign nodule and an FVPTC immunohistochemically, and that its immunohistochemical features and high rate of RASSF1A promoter methylation as that in FVPTCs indicate that it is pathogenetically related to FVPTC.
Category: Endocrine

Tuesday, March 10, 2009 1:00 PM

Poster Session IV # 81, Tuesday Afternoon