Development of a Prognostic Score for Papillary Thyroid Carcinoma Incorporating Ki-67 Labeling Index: MASSIN-K

We previously demonstrated that the Ki-67 labeling index (LI), a marker of cell proliferation, strongly predicts prognosis in patients with papillary thyroid carcinoma (PTC). We subsequently developed a prognostic scoring system incorporating Ki-67 LI.

We enrolled 8540 patients with PTC who underwent curative surgery (median follow-up, 8.7 years). Multivariate Cox regression analysis identified prognostic factors, and regression coefficients from the final models were rounded to generate integer-based scores.

To date, 368, 125, and 22 patients experienced local recurrence (LR), distant recurrence (DR), and carcinoma-related death, respectively. Scores were assigned for age, tumor size, N factor, M factor, Ki-67 LI, and extrathyroidal/extranodal invasion (Ex). The LR score comprised sex (0 or 1), age (0, 1, or 2), T (0 or 2), N (0, 2, or 4), Ki-67 (0 or 4), and Ex (0, 1, or 2). Ten-year LR-free survival rates for low (≤ 2), intermediate (3-4), and high (≥ 5) scores were 98.1%, 95.2%, and 84.5%, respectively (p < 0.001). The DR score comprised sex (0 or 1), age (0 or 3), T (0 or 3), N (0, 2, or 4), Ki-67 (0 or 5), and Ex (0, 3, or 6). Ten-year DR-free survival rates for low (≤ 5), intermediate (6-9), and high (≥ 10) scores were 99.6%, 97.9%, and 85.8%, respectively (p < 0.01). The cause-specific survival (CSS) score for the entire series comprised sex (0 or 2), age (0 or 4), N (0, 1, or 2), M (0 or 4), Ki-67 (0 or 3), and Ex (0, 1, or 2). Ten-year CSS rates for low (≤ 3), intermediate (4-5), and high (≥ 6) scores were 100%, 99.8%, and 97.1%, respectively (p < 0.01). In M-negative patients, the CSS score comprised sex (0 or 1), age (0 or 3), N (0, 1, or 2), Ki-67 (0 or 3), and Ex (0, 1, or 2). The 10-year CSS rate for high-score (≥ 6) patients was 96.9%, significantly lower than those for low- and intermediate-score patients (100% and 99.8%, respectively; p < 0.01).

MASSIN-K, a prognostic scoring system incorporating Ki-67 LI, showed good prognostic discrimination in patients with PTC. External validation is required as a further study.