Residual mesorectal lymph node involvement following neoadjuvant combined-modality therapy: Rationale for radical resection?

Background: In order to evaluate the impact of preoperative radiation and chemotherapy (combined modality therapy, or CMT) on primary rectal cancer and mesorectal lymph nodes (MLNs), middle and lower third rectal cancers were resected with total mesorectal excision (TME) and assessed for frequency of MLN retrieval and residual MLN involvement. Methods: Between 1990 and 2001, 187 consecutive patients underwent abdominoperineal resection (APR) or low anterior resection (LAR) for locally advanced (endorectal ultrasound [ERUS] stage, T _3-4) mid and distal rectal cancer following preoperative CMT. Sphincter preservation was possible in 150 patients (80%). The mean number of retrieved MLNs was 10.6. Pre-CMT ERUS stage was compared with final pathologic stage. Results: Comparison of pre-CMT ERUS stage with pathologic stage revealed a decrease in T stage in 93 patients (49%), as well as a decrease in the percentage of individuals with positive MLNs, from 54% to 27% (P < .0001). The overall incidence of positive MLN involvement was 27%, and incidence paralleled pathologic T stage (pT): pT₀ = 7%, pT₁ = 8%, pT₂ = 22%, pT₃ = 37%, and pT₄ = 67%. Conclusions: Following preoperative CMT, the incidence of residual MLN involvement remains significant and parallels increasing pT stage. Therefore, the standard of care for locally advanced distal rectal cancer should continue to include formal rectal resection (TME).