Aggressive variants of papillary thyroid microcarcinoma are associated with high-risk features, but not decreased survival

Background: This study compares pathologic features and overall survival of classic versus aggressive variants of papillary thyroid microcarcinoma (PMTC). Methods: Patients ≥18 years in the National Cancer Data Base (2004–2015) with the subtypes of classic (cPTMC), tall cell (mTCV), or diffuse sclerosing (mDSV) PTC (≤1 cm) were identified. Overall survival was analyzed by Kaplan-Meier and propensity matched for clinicopathologic and treatment variables. Results: There were 82,056 cPTMC patients, 923 mTCV, and 219 mDSV. Extrathyroidal extension and nodal involvement were more frequent in mTCV and mDSV versus cPTMC (P <.01). mTCV had more distant metastases than cPTMC (P =.02). On multivariable analysis, mTCV (odds ratio 4.19 [3.58–4.92], P <.001) and mDSV (odds ratio 2.76 [1.92–3.97]; P <.01) histologies were predictors of extrathyroidal extension. mTCV was an independent predictor of nodal metastases (odds ratio 1.51 [1.25–1.83], P <.01). Total thyroidectomy and radioactive iodine treatment were more commonly used in mTCV and mDSV patients when compared with cPTMC patients. Despite more aggressive features and more aggressive treatment in mTCV and mDSV patients, there was no difference in overall survival when compared with propensity-matched cPTMC patients. Conclusion: Although mTCV and mDSV have more aggressive pathologic features and were treated more aggressively, there were no differences in overall survival compared with propensity-matched cPTMC patients.