Survival with Follicular and Hurthle Cell Microcarcinoma Compared to Papillary Thyroid Microcarcinoma: A Population Study of 84,532 Patients.

Background: This study compares survival in patients with the rare subtypes of follicular (FTmC) and Hurthle cell (HCmC) microcarcinoma compared to that of papillary thyroid (PTmC) microcarcinoma.
Methods: Patients with FTmC and HCmC were selected from the National Cancer Database 2004-2015 and compared with PTmC. Patient clinicopathological characteristics and overall survival (OS) were analyzed. Multivariable logistic and Cox regression analysis evaluated binary outcomes and predictors of survival. A propensity score matched analysis using age, gender, race, extrathyroidal extension (ETE), nodal status, distant metastasis, radiation, and operation was performed to evaluate the difference in OS with FTmC, HCmC, and PTmC.
Results: We identified 858 FTmC, 476 HCmC, and 82,056 PTmC. FTmC was less likely to have macroscopic ETE compared to PTmC (2.6% vs. 3.1% p = 0.03), but more likely to have distant metastasis (2.3% vs. 0.2%, p < 0.01). FTmC and HCmC were less likely to have nodal metastasis (2.7%, 2.5% vs. 10.9%, p < 0.01). Ten-year OS was decreased in patients with FTmC (91.4%, p = 0.04) and HCmC (89.8%, p < 0.01) compared to PTmC (93.5%). On multivariable analysis, histology was not associated with OS. With HCmC, older age (OR 1.13, p < 0.01) and male gender (OR 2.72, p = 0.03) were associated with decreased OS. In propensity matched analysis, there was no difference in 10-year OS with FTmC and PTmC (91.4% vs. 93.7%, p = 0.54), but HCmC had decreased OS compared to PTmC (89.8% vs. 94.3%, p = 0.04).
Conclusions: Patients with FTmC have comparable OS to those with PTmC, but HCmC has decreased OS especially in older and male patients.