Background: A delay in the diagnosis of differentiated thyroid carcinoma often leads to larger tumors, higher prevalence rates of distant metastasis, and earlier cause-specific deaths. Threshold tumor diameters for extrathyroidal growth, lymph node spread, and distant metastasis in papillary (PTC) and follicular thyroid carcinoma (FTC) remain to be defined.
Methods: A comparative correlation of primary tumor size and extrathyroidal growth, lymph node spread, and distant metastasis was performed for 500 institutional patients who received surgery for PTC or FTC.
Results: There were 366 patients with PTC (73.2%) and 134 patients with FTC (26.8%). Multifocality (23.5% vs. 9.0%; P < 0.001) and lymph node metastasis (40.2% vs. 19.4%; P < 0.001) were more common in the patients with PTC than in those with FTC. Patients with FTC were older at first diagnosis (51.6 vs. 47.0 years; P = 0.01) compared with the patients with PTC. The FTC tumors were almost twice as large (39.9 vs. 20.6 mm; P < 0.001), and patients had a higher prevalence of distant metastasis (17.9% vs. 6.3%; P < 0.001). When primary tumor diameter was accounted for, cumulative risks of extrathyroidal growth and lymph node metastasis were higher in patients with PTC than in patients with FTC (P < 0.001; log-rank test). In striking contrast, the cumulative risk of distant metastasis was the same for PTC and FTC tumors of equal size (P = 0.89; log-rank test) and increased once the primary tumor size was > 20 mm. Pulmonary metastasis was an earlier event than bone metastasis.
Conclusions: The data suggested that earlier intervention is warranted to keep suspicious thyroid nodules from growing > 20 mm (or greater than T1) and spreading to distant organs.