Necessity of External Iliac Lymph Nodes and Inguinal Nodes Radiation in Rectal Cancer with Anal Canal Involvement

Abstract

<h3>Purpose/Objective(s)</h3> Considerable controversy still exists in regard to the elective irradiation of the external iliac lymph nodes (EIN) and inguinal nodes (IN) in rectal cancer with anal canal involvement (ACI) without convincing evidence. This study aimed to explore the necessity of the EIN and IN region in clinical target volume (CTV) for rectal carcinomas covering the anal canal region. <h3>Materials/Methods</h3> Between January 2006 and April 2017, a total of 399 consecutive patients with primary low rectal cancer located below the peritoneal reflection identified with magnetic resonance imaging (MRI) and received neoadjuvant chemoradiotherapy (NCRT), without elective EIN and IN irradiation, followed by surgery were reviewed in this study. Patients were divided into two groups according to whether the lower edge of the tumor came in contact with the anal canal (P group, n=109) or not (Rb group, n=290). Overall survival (OS), disease-free survival (DFS), locoregional recurrence-free survival (LRFS) and distant metastasis-free survival (DMFS) were compared using inverse probability of treatment weighting (IPTW) and multivariable analyses. The EIN and IN failure rates were compared between the two groups using the Fisher's exact tests and Gray's test. <h3>Results</h3> After a median follow-up of 77 months, P group showed a similar adjusted proportion and 5-year cumulative rate of EIN failure as Rb group. The adjusted proportion (6.3% versus 0.7%; P=0.008) and 5-year cumulative rate (7.4% versus 0.8%; P<0.001) of IN failure in P group was higher compared with Rb group. However, there were no significant differences in the adjusted 5-year OS (HR 1.48, 95% CI 0.95-2.25, p=0.0810), DFS (HR 1.40; 95% CI 0.95-2.08, p=0.0910), DMFS (HR 1.23, 95% CI 0.78-1.96, p=0.374) and LRFS (HR 1.29, 95% CI 0.76-2.19, p=0.346) between the two groups. The station of the anal canal involvement also showed no effect on OS (HR 1.30, 95% CI 0.76-2.22, P=0.336), DFS (HR1.31, 95% CI 0.82-2.08, P=0.260), DMFS (HR 1.23, 95% CI 0.78-1.96, p=0.374) or LRFS (HR 1.29, 95% CI 0.76-2.19, p=0.346), respectively. <h3>Conclusion</h3> It may be feasible to exclude the EIN and IN from the CTV during NCRT for rectal cancer with ACI, further studies are needed to clarify whether the cranial border of the CTV can be limited.