Lymph node dissection after primary surgery and neoadjuvant radiochemotherapy of rectal cancer. Interim analysis of a multicenter prospective observational study (OCUM)

The OCUM trial (NCT01325649) aims to clarify whether low rates of local recurrence are also achieved when the indications for neoadjuvant radiochemotherapy are not based on the clinical TNM staging but on preoperative magnetic resonance imaging with measurement of the tumor distance to the circumferential resection margin. In this interim analysis the lymph node status in OCUM patients was investigated as a surrogate parameter for quality of surgery and histopathological work-up.Until now a total of 560 patients have been included in this study. Total mesorectal excision (TME) without pretreatment was undertaken in 338 patients (60.4 %) and neoadjuvant radiochemotherapy was administered in 222 (39.6 %) patients. The histological work-up was performed according to the guidelines of the German Association of Pathologists. Data are given as median values and ranges in brackets.The lymph node yield was 24 (7-79) in 338 patients undergoing primary TME surgery without pretreatment, while 20 (3-56) lymph nodes were identified in patients after neoadjuvant radiochemotherapy (p = 0.001). A minimum of 12 lymph nodes were analyzed in 335 out of 338 patients (99.1 %) and in 209 out of 222 patients (94.1 %) following neoadjuvant radiochemotherapy (p = 0.001). Lymph node metastasis was identified (p = 0.362) in 116 out of 338 patients without pretreatment (34.3 %) and in 71 out of 222 patients after neoadjuvant radiochemotherapy (32.0 %). Patient age did not influence the number of identified lymph nodes or rate of lymph node metastasis.In this trial the number of identified lymph nodes suggests that the quality of surgery and histopathological work-up were adequate compared to the standards defined by national guidelines. Neoadjuvant radiochemotherapy led to a reduced lymph node yield compared to surgery without pretreatment; however, this did not influence the rate of lymph node metastasis.