Mapping of lateral pelvic lymph node recurrences in rectal cancer: a radiation oncologist’s perspective

Purpose: Patterns of locoregional rectal cancer recurrences following total mesorectal excision (TME) were analyzed to define the irradiation volume, especially the lateral pelvic lymph node (LPLN). Materials and methods: Of 1243 patients who underwent TME without pelvic radiotherapy between 2005 and 2012, the data of 826 patients with rectal adenocarcinoma without distant metastases were analyzed for relapse patterns, categorized as distant and locoregional (anastomosis, mesorectum, presacral area, and LPLNs) failure. Results: The median follow-up was 61.8 months. The 5-year local recurrence-free, distant metastasis-free, overall survival rates were 88, 82, and 89%, respectively. Relapse occurred in 108 (13%) patients: 90 (11%) had distant and 28 (3%) had locoregional failure. Eight patients had LPLN recurrence: the 2 recurrences from upper rectal cancers occurred near the bifurcation of the common iliac artery into the external and internal iliac vessels; the 6 mid-lower rectal cancers had 16 recurrences near the internal iliac and obturator arteries—five occurred anterior to the obturator artery and posterior to the external iliac artery, superior to the femoral head. LPLN recurrence was associated with pN2 stage, perinodal extension, and lymphovascular invasion. Conclusion: The LPLN component of pre- or postoperative irradiation volumes could potentially be optimized based on our mapping data. However, since patients in our institution at high risk for relapse received either preoperative or postoperative chemoradiation, further analyses are needed to confirm our findings.