Advancing Education, Research, and Quality of Care for the Head and Neck oncology patient.
Introduction: Micropapillary thyroid carcinoma (mPTC), defined as primary tumors less than one centimeter in size, has been previously recognized as a unique clinical entity with a relatively good prognostic outcome and low mortality rates. The 2015 American Thyroid Association guidelines allow for appropriate surveillance of patients with mPTC when no suspicious clinical nodal disease or extrathyroidal extension is present. However, a subsection of patients with mPTC do present with advanced locoregional disease and require aggressive surgical treatment. Unfortunately, limited data exists to predict which patients with mPTC are at higher risk for locoregional spread. Therefore, we aim to investigate which characteristics place patients into a higher risk category to presentat with nodal disease and to investigate comparative survival outcomes of mPTC as compared to early-stage papillary thyroid cancer (PTC).
Methods: The National Cancer Database was queried for patients diagnosed with early stage (cT0-T2, M0) PTC between 2004-2016. Micropapillary thyroid cancer (mPTC) was defined as clinical T0 disease that was defined as pathological T1a after surgical resection. mPTC patients were compared to those with T1a and T2a primary tumors. Logistic regression assessed for risk factors associated with nodal disease in mPTC. Kaplan Meier and Cox Proportional Hazards (CPH) analyses assessed overall survival (OS) and all-cause mortality, respectively.
Results: 192,052 PTC patients (79.7% female) were included for analysis, of which 2.0% were mPTC. The mean age was 49.6 ± 14.6 years. 3,607 mPTC patients had N0 disease, 295 with N1 disease. Among mPTC patients, multivariable logistic regression demonstrated that age ≥55 years (OR 0.74; p=0.021), female sex (OR 0.27; p<0.001), and Black (OR 0.56; p=0.044) or Asian race (OR 1.90; p=0.023) were predictors of nodal disease. In mPTC, N1B disease portended worse 10-year overall survival (OS) than N0 (71.3% vs. 89.2%, p<0.001) but there was no significant difference when comparing mPTC patients with N0 and N1a disease. mPTC exhibited worse 10-year OS than cT1a tumors with N1a (84.2% vs. 93.1%, p<0.001) and N1b disease (71.3% vs. 88.8%, p<0.001). On multivariable CPH analysis, mPTC was associated with worse mortality than both T1a and T1b tumors.
Conclusions: Although a low proportion of patients with PTC have mPTC disease, it portends a lower 10-year OS when compared to patients with T1a and T1b, regardless of regional nodal disease burden. Additionally, survival rates for mPTC decreases as nodal disease increases. Finally, continued investigation should be performed to determine the utility of active surveillance versus thyroid lobectomy for mPTC patients with N0 disease, as 10-year OS is lower in these patients than in PTC patients with T1bN0 or T2N0.