Effects of Radiotherapy (RT) and Chemoradiotherapy (CRT) on Lymph Nodes (LNS) In Patients with Rectal Cancer: Evaluation of Numbers of Retrieved LNS and LN Size

ABSTRACT Background In patients with colorectal cancer, retrieval of 12 or more LNs has been reported to be associated with better outcomes. Preoperative RT or CRT reduces the number of retrieved LNs. The effects of RT and CRT on LNs may be different between LNs inside and LNs outside the radiation field. Methods The study group comprised 368 patients with a cStage II/Stage III adenocarcinoma of the rectum between 1991 and 2010. 108 received surgery alone (S group), 158 received preoperative RT with 20 Gy in 10 frs. plus IORT with 15 Gy (RT20 group), and 102 received preoperative RT 40 or 45 Gy in 20 or 25 frs. plus concurrent chemotherapy with oral UFT or S-1 (RT45 group). The sizes of LNs (shortest axis, longest axis, and area) were measured on specimens stained with hematoxylin and eosin, using a computer digitizer. LNs were divided into 2 groups according to their distribution, inside the radiation field and outside. Results The total number of retrieved LNs was 1718 in the S group, 2337 in the RT20 group, and 917 in the RT45 group. The total number of retrieved LNs was significantly lower in the RT45 group (9.0 ± 6.9) than in the S group (15.8 ± 10.6) and the RT20 group (14.8 ± 9.1). (p  Conclusions Our results showed that the response of LNs to RT/CRT differed between inside and outside of the radiation field. The numbers of retrieved LNs should be separately assessed inside and outside the radiation field to ensure accurate disease staging. Disclosure All authors have declared no conflicts of interest.