Exploring the prognostic value of positive lymph node ratio in stage Ⅲ colorectal cancer patients and establishing a predictive model

Background and purpose: Currently, for patients with mid-to-low locally advanced rectal cancer and potentially resectable T4bM0 colon cancer, guidelines recommend neoadjuvant therapy strategies to enhance the response rate and increase the likelihood of conversion surgery. Among these patients, ypⅢ stage colorectal cancer (CRC) is assessed using the Union for International Cancer Control (UICC)/American Joint Committee on Cancer (AJCC) TNM staging system for postoperative pathological features. However, neoadjuvant therapy can lead to lymph node regression in the surgical area, resulting in an insufficient number of detected lymph nodes (less than 12), preventing classification according to conventional TNM staging. Thus, TNM staging often fails to predict the prognosis of ypⅢ patients who have undergone neoadjuvant therapy. This study aimed to evaluate the prognostic value of the positive lymph node ratio (LNR) in ypⅢ stage CRC patients treated with neoadjuvant therapy. Methods: Retrospective data was collected from ypⅢ stage CRC patients who received neoadjuvant therapy and underwent radical surgery at Fudan University Shanghai Cancer Center between 2008 and 2018. Collect clinical pathological characteristics such as age, gender, primary tumor location, tumor differentiation grade, pathological staging, and whether the patient has relapsed or died during follow-up at the time of surgery. Inclusion criteria: CRC patients who have received neoadjuvant therapy and surgery and have been confirmed to be stage Ⅲ by postoperative pathological examination. Exclusion criteria: ① Preoperative imaging examination or intraoperative exploration reveals distant organ metastasis; ② History of malignant tumors in the past; ③ Multiple primary CRC. This study was approved by the medical ethics committee of Fudan University Shanghai Cancer Center (ethics number: 050432-4-2108*). The R software survminer package (surv_cutpoint algorithm) was used to calculate the optimal cutoff value for LNR relative to disease-free survival (DFS), and patients were divided into low and high LNR groups accordingly. Clinical pathological characteristics and DFS were compared between the two groups. COX proportional hazards regression models were employed to identify adverse pathological features, and survival plots along with prediction models for DFS were generated using the survival and rms packages. Results: A total of 489 patients were included, comprising 289 males and 200 females, with a median age of 56 years (23-80 years) and a median follow-up time of 1 062 d. During the follow-up period, 164 patients (33.5%) died. In the entire cohort, 204 (41.7%) patients had fewer than 12 lymph nodes detected. The optimal cutoff value for LNR was 0.29, classifying 317 patients into the low LNR group (LNR≤0.29) and 172 patients into the high LNR group (LNR>0.29). The high LNR group exhibited shorter DFS compared to the low LNR group [hazard ratio (HR)=2.103, 95% CI: 1.582-2.796, P<0.000 1]. Multivariate COX regression indicated that LNR was an independent prognostic factor for DFS (HR=1.825, 95% CI: 1.391-2.394, P<0.001). The inclusion of LNR in a multicategory DFS nomogram prediction model effectively assessed DFS in stage Ⅲ CRC patients who had undergone neoadjuvant therapy. Conclusion: LNR is an independent prognostic factor for ypⅢ stage CRC patients, showing good predictive power for DFS when combined with other adverse pathological features. Therefore, incorporating LNR as a supplement to TNM staging can improve the accuracy of CRC prognosis assessment.