The optimum number of retrieved lymph nodes for locally advanced rectal cancer following short-course preoperative radiotherapy: A study by fat clearance.

Abstract

449 Background: The optimum number of retrieved lymph nodes following preoperative radiotherapy and surgery for locally advanced rectal cancer is still controversial. This study is designed to confirm the least number of retrieved lymph nodes for locally advanced rectal cancer following 30Gy/10f short-course preoperative radiotherapy. Methods: From Aug 2002 to Mar 2010, two hundred and twelve patients with locally advanced rectal cancer received 30Gy/10f preoperative radiotherapy (BED: 36Gy), standardized total mesorectal excision and fat-clearance based pathological evaluation in Beijing Cancer Hospital. The size of retrieved lymph nodes (LNs) was recorded. The sequence of LNs was arranged by a descending sort by retrieved nodes' size and the serial number of the largest metastatic lymph node (mLN) was recorded. The serial number of the first largest mLN is regarded as the least number of LNs to distinguish ypN+ status. The cumulative accuracy of ypN stage by variable numbers of LNs was calculated and analyzed. Results: There were total 4,669 retrieved LNs and 354 mLNs. The median retrieved LNs number was 21 (range 4-61). The ypN positive rate was 40.6%. The peak-value of quantitive distribution of LNs and mLNs was observed in 1-2mm and 3-4mm level. The incidence of retrieving mLNs shows an intensifying tendency for increasing size of LNs. The analysis for sequence of LNs sorting suggested that 85.4% of cases could confirm their ypN stage by the first largest LN. The cumulative accuracy ascended to 95.1% or 98.1% when the first 5 or 9 largest LNs were retrieved. Conclusions: For rectal cancer following 30Gy/10f preoperative radiotherapy, retrieving 12 or more lymph nodes seems not to be mandatory for confirming ypN stage. The accuracy in confirming negative ypN stage when retrieving 5 or 9 largest nodes is sufficient for majority of patients. In those cases that could not retrieve 5 or more nodes by routine fixation, fat clearance is indispensable. No significant financial relationships to disclose.