Are the numbers of retrieved lymph nodes (LNs) within and outside the radiation field significant prognostic factors in patients who received chemoradiotherapy (CRT)?

Abstract

510 Background: We had presented last year that the number of lymph nodes (LNs) significantly decreased within the radiation field, but not outside the radiation field in rectal cancer patients who received preoperative chemoradiotherapy (CRT) as compared with patients who underwent surgery alone. In the present study, we examined the relation between survival and the number of LNs within and outside the radiation field, separately. Methods: The study group comprised 210 patients who underwent radical surgery for clinical stage II or III rectal cancer from 1991 through 2010. A total of 108 patients underwent surgery alone (S group), and 102 patients received preoperative CRT, 40 or 45 Gy with concurrent oral UFT or S-1, (CRT group). LNs were divided into two groups according to their distribution; within the radiation field (within the mesorectum) or outside the radiation field. Results: Patient demographics did not differ between the groups. The number of LNs examined was 2617, of which 290 (11%) were metastatic. The mean total number of LNs was significantly higher in the S group (16 ± 11) than in the CRT group (9 ± 7; p<0.01). The number of LNs within the radiation field was significantly higher in the S group (6 ± 6) than in the CRT group (4 ± 4; p<0.01), but the number of LNs outside the radiation field did not differ. The total number and the number of metastatic LNs outside the radiation field did not differ between the groups, however, the number of metastatic LNs within the radiation field was significantly higher in the CRT group (S group, 2 ± 2; CRT group, 3 ± 4; p<0.01). In the S group, the total number of LNs and the number of LNs within the mesorectum were both prognostic factors in pStage II disease. A total number of ≥18 LNs and ≥5 LNs within the mesorectum were associated significantly with better outcomes. The number of metastatic LNs within the mesorectum was a prognostic factor in pStage III disease. In the CRT group, however, the total number of LNs and the number of LNs within the mesorectum were not related to survival. Conclusions: The number of LNs within the mesorectum might be a prognostic factor in patients who receive surgery alone, but not in patients who receive CRT.