Simultaneous integrated boost intensity-modulated radiation therapy targeting clinically involved extramesorectal...

Consensus is lacking regarding the management of extramesorectal lymph nodes (EMLN) in rectal cancer. Using simultaneous integrated boost intensity-modulated radiation therapy (SIB-IMRT), we targeted involved EMLN and reserved lateral pelvic lymph nodal dissection (LPLND) for nonresponders. The primary aim of this work was to determine the proportion of patients who avoided LPLND and to establish the pathological EMLN positivity rate.

Consecutive patients with rectal cancer with suspicious EMLN [short axis dimension (SAD) ≥ 7 mm], receiving SIB-IMRT as part of neoadjuvant chemoradiotherapy and subsequently undergoing total mesorectal excision (TME) or watch-and-wait, were included. Our primary objective was to determine the proportion of patients with a good nodal response (EMLN SAD < 5 mm) who were spared LPLND. The 3-year locoregional relapse rate, distant metastasis-free survival (DMFS) and overall survival (OS) were also assessed.

Of the 61 patients studied, 38 (62.3%) responded well to SIB-IMRT. In this group, 32 patients underwent TME alone and six were observed as per watch-and-wait. The remaining 23 (37.7%) patients with persistent EMLN received TME with LPLND. On pathological evaluation, 7 (30.4%) patients had positive nodes while 16 (69.6%) were negative. At a median follow-up of 32 months (95% CI 23.3-40.7 months), 10 (16.4%) patients developed distant metastases while none had local or pelvic relapse. The resultant 3-year DMFS and OS for the whole cohort were 84.4% and 95.1%, respectively. Overall, 5/61 (8.2%) patients encountered radiation-induced toxicity of grade 3 or above and 8/55 (14.5%) patients had severe postoperative complications.

SIB-IMRT targeting EMLN followed by selective LPLND exhibits excellent oncological outcomes. While patients responding to SIB-IMRT safely avoid LPLND, the potential for increased morbidity in nonresponders must be considered.