Assessing the clinical utility of tumor invasion proportion of lymph nodes for enhanced risk stratification in N1 colorectal cancer.

N staging systems are paramount clinical features for colorectal cancer (CRC). In N1 stage (N1) CRC, patients present with a limited number of metastatic lymph nodes, yet their prognoses vary widely. The tumor invasion proportion of lymph nodes (TIPLN) has gained attention, but its prognostic value in N1 CRC remains unclear. We retrospectively analyzed 416 N1 CRC patients who underwent radical surgery from January 2014 to December 2018, reviewing 713 hematoxylin and eosin (H&E)-stained slides to assess TIPLN. Overall survival was the primary outcome in our study. Using restricted cubic splines, we explored the relationship between TIPLN and prognosis, with Cox regression and subgroup analyses adjusting for potential confounders. We found that increased TIPLN was associated with an unfavorable prognosis. At a cut-off value of 50%, patients with high-TIPLN exhibiting poorer outcomes than their low-TIPLN counterparts (hazard ratio: 3.77, P < 0.001). Furthermore, high-TIPLN was confirmed as an independent risk factor for overall survival (hazard ratio: 3.12, P < 0.001) after adjusting for clinical confounders. Notably, TIPLN could also enhance risk stratification within the T and N stages, where patients with low-risk (T1-3 stage) and high-TIPLN demonstrated poorer overall survival compared to those with high-risk (T4 stage) and low-TIPLN (hazard ratio: 2.54, P = 0.021). In conclusion, TIPLN is a promising prognostic indicator for N1 CRC patients that complements traditional N staging system for a more comprehensive evaluation. Integrating TIPLN into the TNM staging system could enhance risk stratification and guide treatment decisions.