We investigated whether routine elective irradiation of a clinically negative inguinal node (IGN) is necessary for patients with locally advanced distal rectal cancer and anal canal invasion (ACI).

We reviewed retrospectively 1,246 patients with locally advanced rectal adenocarcinoma managed using preoperative or postoperative chemoradiotherapy and radical surgery between 2001 and 2011. The patients' IGN was clinically negative at presentation and IGN irradiation was not performed. ACI was defined as the lower edge of the tumor being within 3 cm of the anal verge. Patients were divided into two groups, those with ACI (n = 189, 15.2%) and without ACI (n = 1,057, 84.8%).

The follow-up period was a median of 66 months (range, 3-142 months). Among the 1,246 patients, 10 developed IGN recurrence; 7 with ACI and 3 without ACI. The actuarial IGN recurrence rate at 5 years was 0.7%; 3.5% and 0.2% in patients with and without ACI, respectively (p < 0.001). Isolated IGN recurrence occurred in three patients, all of whom had ACI tumors. These three patients received curative intent local treatments, and one was alive with no evidence of disease 10 years after IGN recurrence. Salvage treatments in the other two patients controlled successfully the IGN recurrence for >5 years, but they developed second malignancy or pelvic and distant recurrences. Seven patients with non-isolated IGN recurrence died of disease at 5-22 months after IGN recurrence.

The low IGN recurrence rate even with ACI and the feasibility of salvage of isolated IGN recurrence indicated that routine elective IGN irradiation is not necessary for rectal cancer with ACI.