Is the omission of the external iliac or upper pelvic lymph nodes from elective irradiation safe in selected anal canal squamous cell cancers?

Background: Guidelines recommend elective irradiation of the external iliac and upper pelvic lymph nodes (LNs) regardless of clinical stage, but the supporting evidence for this recommendation is limited.

Methods: We conducted a retrospective analysis of 68 consecutive patients with squamous cell carcinoma of the anal canal who underwent volumetric modulated arc therapy chemoradiation, excluding external iliac LNs from elective irradiation. In patients with negative bilateral inguinal LNs, both external iliac regions were omitted, while in those with unilateral positive inguinal LNs, only the ipsilateral external iliac region was included and the contralateral side was omitted.