Risk Stratification of Follicular Variant of Papillary Thyroid Carcinoma
Marina Vivero, Stefan Kraft, Justine A Barletta. Brigham and Women's Hospital, Boston, MA; Massachusetts General Hospital, Boston, MA
Background: Recent studies have described an encapsulated and an infiltrative form of follicular variant of papillary thyroid carcinoma (FVPTC). While encapsulated tumors have been reported to have virtually no metastatic potential or recurrence risk, infiltrative tumors have been found to have a significant metastatic potential and a risk of recurrence. In our experience, a substantial number of FVPTCs are neither fully encapsulated nor infiltrative, but instead are partially-encapsulated (PE) or well-circumscribed (WC). The aim of this study was to investigate the metastatic potential and recurrence risk of PE/WC FVPTCs in comparison with that of encapsulated and infiltrative tumors.
Design: We studied 78 FVPTCs resected at our institution between 2000 and 2002. All tumors were evaluated histologically and characterized as encapsulated, PE/WC, or infiltrative. For each case the following parameters were recorded: extrathyroidal extension, margin status, vascular invasion, and lymph node (LN) status. Follow-up clinical information was obtained from electronic medical records.
Results: The tumors in our cohort were from 66 women and 12 men, with a mean age at resection of 50 years. Twenty-seven (35%) tumors were encapsulated, 36 (46%) were PE/WC, and 15 (19%) were infiltrative. LN status was available for 33 (42%) cases, and clinical follow-up was available for 67 (86%) cases. The mean follow-up time was 100 months. LN metastases were absent in all 15 cases of encapsulated tumors and all 9 cases of PE/WC tumors with sampled lymph nodes, but were present in 7 of 9 (78%) cases of infiltrative tumors with sampled LNs. Thus, the LN status was significantly different between PE/WC and infiltrative groups (p=0.0023). No patients with encapsulated tumors recurred, one (3%) patient with a PE/WC tumor recurred, and two (15%) patients with infiltrative tumors recurred. Although the difference in recurrence risk was not significantly different between PE/WC and infiltrative groups (p=0.20), this could be the result of the small cohort size. Interestingly, the one patient with a PE/WC tumor that experienced a recurrence was the only patient in this group that had a positive margin. This patient had a tumor bed recurrence 7 years after initial resection.
Conclusions: Our results demonstrate that PE/WC FVPTCs have a very low metastatic potential/recurrence risk, suggesting that these tumors behave in an indolent fashion similar to that of encapsulated tumors and indicating that they should be distinguished from more aggressive infiltrative tumors.
Tuesday, March 20, 2012 1:00 PM
Poster Session IV # 16, Tuesday Afternoon