Subcapsular Sclerosing Variant (SSV) of Papillary Thyroid Microcarcinoma (PTMC): Clinicopathologic and Molecular Features
Renu K Virk, Constantine L Theoharis, Pei Hui, Manju Prasad. Yale School of Medicine, New Haven, CT
Background: Peripheral location of the papillary thyroid microcarcinoma (PTMC) has been suggested to be a high-risk histologic feature that correlates with aggressive behavior. Conventionally PTMC are not further subtyped. Here we define a distinct subtype of PTMC, the subcapsular sclerosing variant (SSV) along with its clinicopathological and molecular features.
Design: We identified PTMC diagnosed during 2010-2012 that met the following criteria: peripheral location (capsular or subcapsular), abutting thyroid capsule along at least 20% of the tumor's circumference, prominent tumor-associated stromal fibrosis, sclerosis and/or desmoplasia), and infiltrative tumor borders. The clinicopathological features were reviewed and BRAFV600E mutational analysis was performed by single strand conformational polymorphism.
Results: The patients (n=39) included 31 women and 8 men (F: M- 4:1), aged 23 to 75 years (mean 50). The tumor size ranged from 2 mm to 10 mm (mean 7 mm). Thirty-four (87%) tumors harbored the BRAFV600E mutation. Twelve SSV (31%) showed minimal extrathyroidal extension (ETE). Lymph node metastasis (LNM) was present in 30% (n=10/33) of tumors. However, in node negative patients, the tumor was upgraded from T1 to T3 based on ETE in 22% (n=5/23). Area of contact of tumor (in percentage) with thyroid capsule ranged from 20% to 90%. Interestingly, incidence of ETE increased from 18% (n=5/27) to 58% (n= 7/12) when the area of contact increased from <50% to ³50% respectively.
Conclusions: Subcapsular sclerosing variant of PTMC has a distinctive morphology, and location within the thyroid. They are associated with minimal microscopic ETE, lymph node metastasis, and with BRAFV600E mutation in a significant proportion of cases. Identification and segregation of this subset from other PTMC may be helpful in exploring long-term disease outcome.
Monday, March 4, 2013 1:45 PM
Proffered Papers: Section H, Monday Afternoon