Effect of chemoradiotherapy (CRT) for rectal cancer on the lymph nodes (LNs): Exploration of the number of retrieved LNs, number of metastatic LNs, and the size of LNs.

Abstract

651 Background: For accurate staging of colon cancer, 12 or more LNs are recommended to be explored. Although the total number of LNs in rectal cancer was reported to be decreased after CRT, the number of LNs to be explored is not yet clear. We investigated the number of retrieved LNs, number of metastatic LNs, and the LN sizes within the radiation field in comparison with those outside the radiation field, to clarify the influence of CRT. Methods: The subjects were 211 patients with cStage II/III rectal adenocarcinoma who underwent radical surgery between 1991 and 2010. Of these, 111 patients underwent surgery alone (S group) and 100 patients also received preoperative CRT (40 or 45Gy) with concurrent oral UFT or S-1 (RT-group). The numbers of LNs were reviewed by pathological chart, and HE-stained specimens were examined with a digitizer to evaluate the LN sizes (short-axis, long-axis and area). Results: A total of 2049 LNs were retrieved, of which 230 were metastatic LNs. The average number of retrieved LNs was significantly higher in the S group (16±11) than that in the RT group (9±7) (P < 0.0001). The number of LNs inside the radiation field was significantly higher in the S group (6±6) than that in the RT group (4±4) (P = 0.001), whereas outside the radiation field, there was no significant difference between the two groups (5±4 in the S group vs. 5±4 in the RT group). The short-axis of the retrieved LNs was significantly larger in the S group (within the radiation field: 3.5±2.1 mm in the S group vs. 3.0±1.9 mm in the RT group, P < 0.0001; outside the radiation field: 4.3±2.6 in the S group vs. 3.8±2.4 in the RT group, P = 0.05). Conclusions: Preoperative CRT significantly decreased the total number of LNs compared to the surgery alone, attributable to the decrease in the number of LNs inside the radiation field. CRT reduced the size of the LNs and the degree of reduction was larger in the nodes within the radiation field than in those outside. And it was suggested that CRT also had an effect on the LNs outside the radiation field.