Tall Cell Histology – Comparison of T1 Tall Cell Variant and Classical Papillary Thyroid Carcinoma

Abstract

<h3>Purpose/Objective(s)</h3> Tall cell histology in papillary thyroid carcinoma (PTC) is considered intermediate risk on ATA guidelines. However, it is unclear if patients with T1 tumors with tall cell histology require aggressive treatment. The objective of our study was to compare pathology and outcomes of patients with tall cell histology with that of classical PTC in T1 disease. <h3>Materials/Methods</h3> The study cohort was selected from our departmental database of differentiated thyroid cancers treated surgically between 1985 and 2015 (n=6,259). PTC cases demonstrating ≥30% tall cells were considered as tall cell variant (TCV). All T1 classical PTC and TCV were identified. Patient and tumor characteristics were compared between groups by Fisher exact test, chi-squared test or two sample t test. Survival and recurrence outcomes were compared using the log-rank test and Kaplan-Meier method. <h3>Results</h3> There were 712 TCV and 2,354 classical PTC patients with T1 tumors. Total thyroidectomy and lobectomy were done in 622 and 90 TCV patients compared to 1883 and 471 classical PTC patients. Central neck dissection was done in 140 TCV and 420 classical PTC patients. Lateral neck dissection was done in 89 TCV and 323 PTC patients. 208 and 87 TCV patients were N1a and N1b compared to 385 and 306 classical PTC patients. There was no significant difference between TCV and classical PTC in gender, age >55 years and vascular invasion. Compared to classical PTC, TCV cases were significantly more likely to demonstrate microscopic extrathyroidal extension (p<0.01), multifocality (p<0.01), larger size (mean 1.30cm in tall cell and 1.15cm in classical PTC) (p=0.02), less encapsulation (p<0.01) and treatment with radioactive iodine (p<0.01). Rates of central nodal disease were significantly higher in TCV cases (p<0.01), but there was no significant difference in rates of lateral nodal disease (p=0.61). There was no significant difference in overall survival (p=0.73), disease-specific survival (p=0.69) or locoregional recurrence (p=0.08). Of those that underwent lobectomy only, there was no significant difference in locoregional recurrence between classical PTC and TCV cases (p=0.79). For TCV cases only, there was no significant difference in locoregional recurrence between those that underwent lobectomy compared to those that had total thyroidecomy (p=0.08). <h3>Conclusion</h3> Despite having a higher rate of microscopic extrathyroidal extension and regional metastases, patients with T1 tall cell tumors have similar oncologic outcomes to patients with classical PTC.