Threshold Primary Tumour Sizes for Nodal and Distant Metastases in Papillary and Follicular Thyroid Cancers

Background: In papillary and follicular thyroid cancers (PTC, FTC), nodal and distant metastasis aregenerally considered important determinants of recurrence and survival, respectively. However, there is noconsensus about the threshold primary tumour size (PTS) for these determinants. The aim of this study was toassess size relationships for developing nodal, pulmonary, bone and overall distant metastases.
Methods: Thisprospective study covered 139 (93 females and 46 males) consecutive biopsy proven patients with PTC (114/139,mean age 41.0 ±15.7 years, M: F, 35%:65%) and FTC (25/139, mean age 39.2 ± 14.3 years, M: F: 24%:76%).
Results: Average primary tumor size was 23.4 ± 11.1 mm and 26.5 ± 13.1 mm for PTC and FTC respectively(p value=0.223). Nodal metastasis was found more common in PTC than FTC (49% vs 28%, p value <0.05),whereas overall distant metastasis was approximately the same (13% and 24%, p value =0.277); however, bonemetastasis was significantly higher in FTC than PTC (24% vs 5%, p value <0.05). Cumulative risk for nodaland distant metastases for FTC and PTC starts at PTS <20 mm and may indicate an unusual aggressive tumorbehavior in the studied population. Highest cumulative risk for nodal and pulmonary metastases in PTC andfor bone metastasis in FTC was found to be ≥50 mm PTS.
Conclusion: We conclude that a PTS of <20 mm mayindicate an unusual aggressive tumor behavior with highest cumulative risk for nodal and pulmonary metastasesin PTC and for bone metastasis in FTC with a cutoff of ≥50 mm.