Prognostic role of lymph node-related indices and development/internal validation of a novel nomogram in colorectal cancer patients with synchronous lung metastases: a study based on the SEER database.

[BACKGROUND] Patients with colorectal cancer (CRC) and synchronous lung metastases face a poor prognosis, yet effective prognostic predictors or models for this specific population remain limited. This study aimed to assess the impact of lymph node‑related indices and to construct a novel prognostic nomogram for survival in CRC patients with synchronous lung metastases.

[METHODS] We retrospectively retrieved data for CRC patients diagnosed with synchronous lung metastases between January 2010 and December 2019 from the Surveillance, Epidemiology, and End Results (SEER) database. Based on predefined exclusion criteria, a subset of patients was excluded from the analysis. The optimal cut-off values for lymph node-related indices were determined using X-tile software. Survival differences between groups were assessed with the Kaplan-Meier method and compared using the log-rank test. Cox proportional hazards regression was employed to identify risk factors for overall survival (OS); variables that showed significance in univariate analysis were included in the subsequent multivariate model. Based on the independent prognostic factors identified in the multivariate analysis, a novel nomogram was constructed to predict patient survival. The discriminative ability and predictive accuracy of the nomogram were evaluated using calibration curves and the concordance index (C-index).

[RESULTS] A total of 652 CRC patients with synchronous lung metastases were included in this present study, comprising 328 men and 324 women. The median age of the cohort was 63 years (range, 27-84 years). Patients with total number of lymph nodes (TLN) ≥12 had significantly better OS than those with TLN <12 (3‑year OS: 47.8% . 26.4%; 5‑year OS: 22.7% . 16.2%; P<0.001). Similarly, patients with number of negative lymph nodes (NLN) ≥7 showed superior OS compared to those with NLN <7 (3‑year OS: 51.7% . 21.4%; 5‑year OS: 23.9% vs. 11.7%; P<0.001). Furthermore, OS was significantly poorer in patients with number of positive lymph nodes (PLN) ≥11 than in those with PLN <11 (3‑year OS: 19.3% . 48.0%; 5‑year OS: 4.3% . 23.6%; P<0.001). Multivariate Cox analysis identified TLN, NLN, and PLN as independent prognostic factors for OS [TLN: hazard ratio (HR) =0.627, 95% confidence interval (CI): 0.481-0.816, P=0.001; NLN: HR =0.555, 95% CI: 0.433-0.709, P<0.001; PLN: HR =1.994, 95% CI: 1.485-2.678, P<0.001]. The novel nomogram achieved a C‑index of 0.69 (95% CI: 0.66-0.72). Calibration curves for 3‑year survival probability showed excellent agreement between predicted and observed outcomes.

[CONCLUSIONS] Lymph node‑related indices are significant prognostic factors for CRC patients with synchronous lung metastases. A nomogram incorporating these indices may serve as a practical and effective tool for predicting outcomes in this specific patient population.