a Nomograms for predicting risk of distant metastases in esophageal cancer patients after radical esophagectomy. Differentiation: 1 = high differentiation; 2 = middle differentiation; 3 = low differentiation. LVSI, lymph vascular space invasion: 0 = negative(−); 1 = positive(+). PNI, perineural invasion: 0 = negative(−); 1 = positive(+). b Calibration curve for risk of distant metastases nomogram.