Background: Papillary thyroid carcinoma generally has an indolent nature, but cases demonstrating certain features are progressive. UICC TNM classification is the most widely adopted system to evaluate the biological behavior of this carcinoma, but it is doubtful whether this system that evaluates only the preoperative findings can appropriately reflect patient prognosis. In this study, we established a new staging system (iStage) based on not only preoperative but also intraoperative findings.
Methods: We investigated the prognoses of 5,911 patients with papillary carcinoma without distant metastasis at diagnosis who underwent initial surgery between January 1987 and January 2005 and compared the utility of iStage with that of conventional classification systems, such as UICC Stage, MACIS score (>7 and ≤7), AMES, and CIH classification.
Results: Disease-free survival (DFS) and cause-specific survival (CSS) of patients with stage IVA were better than those of high-risk patients on other systems, and CSS of stage III patients did not differ from stage IVA patients. We established iStage by improving the original UICC stage. We set cutoff age to 55 years, instead of 45. Patients showing significant, not minimal, extrathyroid extension on intraoperative findings underwent T upgrading: tumor size 2 cm or smaller to T3 and larger than 2 cm to T4a. N classification was revised based on the size of node metastasis and extranodal tumor extension: N0, no preoperatively detected regional node metastasis; N1, preoperatively detected regional node metastasis measuring 3 cm or less and without extranodal tumor extension on intraoperative findings; N2, regional node metastasis >3 cm or having extranodal tumor extension on intraoperative examination. Five-year and 10-year DFS and CSS of iStage IVA patients were worse than high-risk patients on other classification systems, and iStage III patients showed a worse DFS, but not CSS, than iStage I or II patients.
Conclusions: We established a new classification system, iStage, based not only on preoperative but also on intraoperative findings, which has high utility. Appropriate intraoperative evaluation is mandatory to grade biological characteristics, including prognosis, of papillary carcinoma.