The Age Threshold of the 8th Edition AJCC Classification Is Useful for Indicating Patients with Aggressive Papillary Thyroid Cancer in Clinical Practice .

Background: Papillary thyroid cancer (PTC) is unique among cancers in that patient age is a consideration in staging. One of the most important modifications in the 8th Edition of the American Joint Committee on Cancer (AJCC) classification, which was introduced in 2018, was to increase the age cutoff for risk stratification in PTC from 45 to 55 years. However, whether this cutoff is useful in clinical practice remains controversial. In the present study, we assessed how well this new age threshold stratifies patients with aggressive PTC.Methods: We retrospectively analyzed the clinicopathological features and overall survival rate of 523 patients with PTC admitted to and surgically treated at a single surgical center. We divided the patients into two groups according to age at PTC diagnosis: ≥55 years and <55 years. Results: We found that the rates of tumor progression, lymph node metastasis (LNM) and distant metastasis were significantly higher in patients ≥55 years than in those <55 years; consequently, TNM stages were significantly higher in older than in younger patients (p<0.05 for all parameters). The risk of tumor progression (T3+T4) was nearly two-fold higher and the risk of LNM (N1) more than four-fold higher in older than in younger patients (p<0.05 for both). No patients <55 years old but 19 patients >55 years old (9.8% of the total group) showed distant metastasis. The rates of microcalcification, vascular and capsular invasion, extrathyroidal extension, irregular tumor shape, multifocality, bilaterality and multiplicity of foci were significantly higher in older than in younger patients (p<0.05 for all). The rate of disease-free survival was significantly lower in older (86.6%) than in younger (98.7%) patients (p<0.0001), and the rate of overall survival was significantly lower in older (90.3%) than in younger (99.4%) patients (p<0.0001).Conclusions: PTC is more aggressive in patients aged ≥ 55 years than in their younger counterparts. This age therefore effectively stratifies PTC patients with a poor prognosis, indicating it is likely to be useful in clinical practice.