Neoadjuvant Therapy For Lateral Pelvic Lymph Nodes: Choosing Between Long Course Chemoradiation Or Short Course Radiotherapy With Consolidation Chemotherapy

Background The response of lateral pelvic lymph nodes (LPLNs) to various neoadjuvant treatments has not been thoroughly investigated. This study aims to compare the effects of long-course chemoradiotherapy (LCCRT) and total neoadjuvant therapy (TNT), i.e., short-course radiotherapy (SCRT) with consolidation chemotherapy, on LPLNs size reduction. The secondary objective is to compare the pathological positivity rates of LPLNs dissection (LPLND), post-neoadjuvant treatment. Methods This is a retrospective analysis based on a prospectively maintained database. Rectal cancer patients registered between January 2020 and December 2021 with radiologically positive LPLNs who underwent neoadjuvant radiation therapy were included. Patients were divided into two groups: LCCRT and TNT. Results Among 1,200 registered rectal cancer cases, 160 had positive LPLNs, with 142 included in the analysis. Sixty-one patients received LCCRT, and 81 patients received TNT. No significant differences were found in T and N staging between the groups. However, the TNT cohort had a significantly higher proportion of metastatic patients (p < 0.001), poorly differentiated tumours (p = 0.021), and extramural venous invasion (p = 0.002). Baseline mean nodal sizes were similar between groups. Post-neoadjuvant nodal sizes were 5.3mm for LCCRT and 6.2mm for TNT, with mean reductions of 5.7mm and 4.6mm, respectively (p = 0.136 & 0.54). Surgery was conducted in 77% of the LCCRT group and 59% of the TNT group, with 22 (46.8%) and 26 (54.1%) undergoing LPLND in their respective groups. The pathological positivity rates for LPLNs were similar (27.3% vs. 23.1%, p = 0.731) Conclusion SCRT with consolidation chemotherapy does not provide a significant advantage over LCCRT in reducing LPLNs size or reducing the need for LPLND.