Interobserver Variability in the Assessment of Extrathyroidal Extension in Papillary Thyroid Microcarcinoma
Renu Virk, Avinash Prasad, Constantine Theoharis, Manju Prasad. Yale School of Medicine, New Haven, CT; Hartford Hospital, Hartford, CT
Background: Extrathyroidal extension (ETE) in papillary thyroid microcarcinoma (PTMC) is associated with local recurrence and central (Level VI) and lateral (Levels II-V) lymph node metastasis. Presence of minimal ETE upstages the PTMC from T1a to T3, adversely affecting prognosis and necessitating treatment with postoperative radioiodine therapy. However, histopathologic assessment of ETE may be difficult due to lack of a well-demarcated thyroid capsule. Moreover, skeletal muscle may be present within thyroid parenchyma, especially in the isthmus as an embryologic remnant. The aim of this study was to assess the inter-observer variability in the assessment of ETE in PTMC using the AJCC criteria.
Design: Two endocrine pathologists independently assessed the presence of ETE in 25 randomly selected PTMCs that were located close to the thyroid capsule. One to three (1-3) representative slides were reviewed for each PTMC tumor. Minimal ETE was assessed using the AJCC staging manual (7th edition) definition, which is tumor extension either in the perithyroidal soft tissue and/or skeletal muscle. Interobserver agreement (Kappa statistics) was calculated Graph Pad software.
Results: There was “moderate” (kappa = 0.453) agreement between the two pathologists for the presence or absence of ETE. Both pathologists agreed for the presence of ETE in 14/25 (56%) tumors and absence of ETE in 5/25 (20%) cases. There was complete disagreement between the two pathologists with respect to 6/25 (24%) cases. Of these six tumors, the first observer reported ETE in 4/6 tumors whereas the second pathologist reported no ETE in those 4/6 tumors. In these six cases, both observers agreed for the involvement of thyroid capsule by the tumor but did not agree for the tumor extension beyond the capsule. There was no disagreement when ETE was diagnosed based on skeletal muscle involvement by the tumor (n=3). Furthermore, there was no discordance with respect to thyroid capsular involvement between the two pathologists in any case.
Conclusions: There is significant interobserver variability with the current AJCC criteria for assessment of ETE in microPTCs. The use of more objective criteria for defining extrathyroidal extension may help improving the consistency in assessing ETE.
Wednesday, March 6, 2013 1:00 PM
Poster Session VI # 36, Wednesday Afternoon