Effect of Elective Inguinal Irradiation in Low Rectal Cancer with Anal Canal Invasion

Introduction: We investigated whether omitting elective inguinal irradiation during neoadjuvant or adjuvant radiation/chemoradiation therapy is feasible for patients with low rectal cancer with anal canal invasion (ACI) and nonpalpable inguinal lymph nodes (ILNs) at presentation. Methods: Ninety low rectal cancer patients with ACI who underwent neoadjuvant or adjuvant radiation/ chemoradiation therapy with or without elective inguinal radiotherapy (RT) between 2011 and 2021 were recruited. None had palpable ILN. The failure pattern, ILN recurrence rate, survival data, and prognostic factors were analysed. Results: Among 81 patients omitting elective inguinal RT, the 3-year ILN failure rate was 4.9%. Meanwhile, there was no inguinal failure with elective RT. One case of isolated ILN failure was successfully salvaged by surgery. In multivariate Cox regression analysis, positive pathological lymph node(s) after neoadjuvant treatment predicted a worse locoregional recurrence-free survival (odds ratio [OR] = 9.066; p ≤ 0.001), distant metastasis recurrence-free survival (OR = 6.426; p = 0.002), and overall survival (OR = 11.750; p ≤ 0.001). Chemotherapy concurrent with RT was associated with better locoregional recurrence-free survival (OR = 33.338; p = 0.001) and overall survival (OR = 13.917; p = 0.006). Grade ≥3 acute and chronic toxicities occurred in 33.3% and 19.8%, respectively, of patients with elective inguinal irradiation, compared with 11.1% and 7.4%, respectively, in patients who did not receive it. Conclusion: Omission of elective inguinal irradiation resulted in a low inguinal failure rate and similar survival outcomes for low rectal cancer patients with ACI. Additionally, it might spare patients from unnecessary acute and chronic RT toxicities.