폐암 N 병기의 비교 분석 및 CT에서 측정한 림프절 크기 활용의 효과

Abstract

Objective: To assess the discrimination performance of N staging in the current 9th edition for lung cancer and to investigate the value of lymph node (LN) size in improving discrimination in clinical N staging.

Materials and Methods: Patients who underwent lobectomy or pneumonectomy for lung cancer from January 2013 to April 2021 were retrospectively analyzed. The clinical and pathologic N categories were reclassified retrospectively according to the 9th edition (N0, N1, N2a, N2b), the 8th edition’s proposal (N0, N1a, N1b, N2a1, N2a2, N2b), and the 7th edition (N0, N1, N2). The prognostic discrimination performance for overall survival (OS) was evaluated using the concordance index (C-index) and compared across each edition. To investigate the value of LN size consideration, the short-axis diameter of the largest clinically positive LN was measured on preoperative CT, and the optimal threshold for a LN size was defined. Prognostic and discrimination performances were assessed based on the LN size cutoff descriptor.

Results: A total of 4753 patients were included in the study. The performance of the 9th edition surpassed that of the 7th edition in both pathologic and clinical staging. Compared with the 8th edition’s proposal, the 9th edition showed comparable performance in pN2 (C-index, 0.560 vs. 0.569, p=0.213) but lower performance in pN1 (0.500 vs. 0.539, p=0.048), resulting in a slightly lower C-index in the total population (0.666 vs. 0.667, p=0.020). For clinical staging, no significant difference of performance between the 9th edition and the 8th edition’s proposal. For LN size analysis, the cutoff value was defined as 15 mm and patients were classified into cN0, cN1 (<15 mm), cN1 (≥15 mm), cN2a, cN2b (<15 mm), and cN2b (≥15 mm). cN1 (≥15 mm) had higher mortality risk relative to cN1 (<15 mm) and the risk of cN1 (≥15 mm) was comparable to that of cN2b. This LN-size classification improved discrimination within the cN1 (C-index from 0.500 to 0.579, p<0.05).

Conclusion: The revision of N category in the 9th edition appears reasonable, as it offers enhanced prognostic discrimination compared with the 7th edition and is comparable to the 8th edition’s proposal. An additional descriptor for N1 would be necessary to further refine the N category. In this regard, the cN (≥15 mm) could be an effective descriptor in the clinical staging of N1.