Nomogram for predicting lymph node metastasis in ypT0–2 rectal cancer after neoadjuvant chemoradiotherapy

PURPOSE: Accurate prediction of lymph node (LN) metastasis is essential for determining completion radical surgery following local excision (LE) in rectal cancer treated with neoadjuvant chemoradiotherapy (CRT). This study aimed to identify predictors of LN metastasis and develop a nomogram to support post-excision decision-making in rectal cancer patients after CRT. METHODS: We retrospectively reviewed 215 patients with pathological stage ypT0-2 rectal cancer who underwent radical surgery following CRT. Pre- and post-CRT magnetic resonance imaging findings and clinicopathological factors were analysed to identify predictors of LN metastasis. A predictive nomogram was subsequently constructed and evaluated using receiver operating characteristic (ROC) curve, calibration curve, decision curve analysis (DCA), and clinical impact curve (CIC). RESULTS: Factors associated with LN metastasis included pre-CRT mrN stage (mrN0 7.3% vs. mrN1 19.4% vs. mrN2 25.0%; p = 0.004), ypT stage (ypT0 2.7% vs. ypT1 13.3% vs. ypT2 19.8%; p = 0.003), and perineural invasion (PNI) (negative 11.1% vs. positive 35.3%; p = 0.013). Multivariable analysis identified pre-CRT mrN stage (p = 0.011), ypT stage (p = 0.033), and PNI (p = 0.036) as independent predictors. The nomogram exhibited acceptable calibration, with the area under the ROC curve of 0.777 (95% CI 0.681-0.874). DCA and CIC revealed the model's potential clinical utility. CONCLUSION: Pre-CRT mrN stage, ypT stage, and PNI were independent predictors of LN metastasis in ypT0-2 rectal cancer following CRT. The developed nomogram may help identify candidates for completion radical surgery after LE, potentially facilitating organ preservation and reducing unnecessary surgical morbidity.