Therapeutic significance of D3 dissection for low rectal cancer: a comparison of dissections between the lateral pelvic lymph nodes and the lymph nodes along the root of the inferior mesenteric artery in a multicenter retrospective cohort study.

Purpose: D3 dissection is the standard treatment modality for locally advanced low rectal cancer in Japan. The benefit of lateral pelvic lymph node (LPLN) dissection (LPLND) and lymph nodes along the root of inferior mesenteric artery (253 LN) dissection (253 LND) for low rectal cancer has often been studied separately, and few studies have investigated their benefit in the same cohort. This study aimed to clarify the therapeutic significance of dissection of the LPLN in comparison to that of dissection of the 253 LN for low rectal cancer.

Methods: We retrospectively evaluated 3508 patients with treatment-naïve stage I-III low rectal cancer who underwent mesorectal excision between 1997 and 2012. They were identified from the Japanese Study Group for Postoperative Follow-Up of Colorectal Cancer database. The rates of metastasis, survival, and therapeutic value index (5-year overall survival (OS) rate multiplied by metastatic rate for lymph node metastasis) were compared between LPLN and 253 LN.

Results: The rates of LPLN metastasis and 253 LN metastasis were 17.9% and 1.5%, respectively. The 5-year OS was significantly different between patients with and without LPLN metastasis (55.0% vs 85.5%, P < 0.0001) and between patients with and without 253 LN metastasis (36.2% vs 83.3%, P < 0.0001). The therapeutic value indexes of LPLN and 253 LN were 9.85 and 0.54, respectively.

Conclusions: LPLND may have more therapeutic value than 253 LND for patients with treatment-naïve low rectal cancer, although both the patients with LPLN metastasis and those with 253 LN metastasis remained to have poor prognosis.