Navigating the Management of Follicular Variant Papillary Thyroid Carcinoma Subtypes: A Classic PTC Comparison

There are three subtypes of follicular variant papillary thyroid carcinoma (fvPTC): completely encapsulated, well circumscribed, and infiltrative. While infiltrative tumors are more aggressive than completely encapsulated, controversy exists regarding management of fvPTC subtypes. We compared the clinicopathologic features of fvPTC subtypes to those of classic PTC (cPTC) to help guide fvPTC management, using cPTC as a reference. A retrospective review was performed on 316 patients with PTC treated at a single institution from 2004 to 2011. There were 197 cPTC and 119 fvPTC tumors, including completely encapsulated (n = 46), well circumscribed (n = 46), and infiltrative (n = 27). Clinicopathologic data were compared between groups. fvPTC patients had larger tumors than cPTC patients (1.6 cm vs. 1.2 cm, p = 0.001), but age, sex, and family history did not differ. Thirty-one percent of cPTC tumors had extrathyroidal extension compared to 0 % of completely encapsulated, 0 % of well-circumscribed, and 52 % of infiltrative fvPTC tumors (p < 0.05). Central lymph node metastasis occurred in 50 % of cPTC compared to 0 % in completely encapsulated, 20 % in well-circumscribed, and 72 % in infiltrative fvPTC tumors (p < 0.05). Notably, lymph node metastasis was significantly lower in completely encapsulated than in well-circumscribed tumors, without a difference in the median number of nodes sampled. There were no differences in lymphovascular invasion or extranodal extension. Like cPTC tumors, infiltrative fvPTC tumors have aggressive clinicopathologic features and thus should be treated similarly. Conversely, completely encapsulated and well-circumscribed tumors have less aggressive features compared to cPTC and are more self-limiting; however, well-circumscribed tumors still have a notable incidence of lymph node metastasis. Clinicians should consider this variability in their management algorithm for fvPTC.