Effect of Lymph Node Count on Pathological Stage III Rectal Cancer with Preoperative Radiotherapy

Abstract

Lymph node (LN) status after surgery for rectal cancer is affected by preoperative radiotherapy. The purpose of this study was to perform a population-based evaluation of the impact of pathologic LN status after neoadjuvant radiotherapy on survival. A total of 1,650 patients receiving neoadjuvant chemotherapy in Surveillance, Epidemiology, and End Results Program (SEER)-registered ypIII stage rectal cancer was analyzed. We identified the optimal cutoff for retrieved LNs as 10 (χ2 = 14.006, P < 0.001), which was validated as an independent prognosis factors in a Cox regression model. Further analysis showed that the LN count was only a prognosis factor with the number from 8 to 16(except for 13).After the number 16, the 5-year survival rate decreased gradually. Collectively, our results confirmed that the number of LNs in yp III stage rectal patients was a prognosis factor only with the numbers from 8 to 16(except for 13). Using the total mesorectal excision technique with an adequate pathologic examination, a large number of LNs retrieved (≥17) might indicate worse tumor response grade and poorer survival.

Figure 1. X-tile analysis of survival data from the SEER registry.

X-tile analysis was performed using patient data, which were equally divided into training and validation sets, from the SEER registry. X-tile plots of the training sets are shown in the left panels, with plots of matched validation sets shown in the smaller inset. The optimal cut-point highlighted by the black circle in the left panels is shown on a histogram of the entire cohort (middle panels), and a Kaplan-Meier plot (right panels). P values were determined using the cutoff point defined in the training set and applying it to the validation set. Figure 1 shows the optimal cutoff point for the ypN (+) patients (10, χ2 = 14.006, P < 0.001).

Figure 2. Log-rank tests of rectal cancer cause-specific survival comparing patients with ≥10 lymph nodes with patients who had <10 nodes for (a) stage ypIIIA: χ2 = 0.121, P = 0.728; (b) stage ypIIIB: χ2 = 22.817, P < 0.001; and (c) stage ypIIIC: χ2 = 13.225, P < 0.001.