Results of a Japanese nationwide multi-institutional study on lateral pelvic lymph node metastasis in low rectal cancer: is it regional or distant disease?

OBJECTIVE: To evaluate whether lateral pelvic lymph nodes (LNs) in low rectal cancer are metastatic disease or part of regional LNs that are amenable to curative resection.

BACKGROUND: It is highly controversial whether lateral pelvic LNs should be considered as regional or distant disease, although the American Joint Committee on Cancer (AJCC) defines internal iliac LNs as regional LNs of rectal cancer.

METHODS: Data of patients with stage I to III low rectal cancer who underwent curative resection from 1978 to 1998 were extracted from the multi-institutional registry of large bowel cancer in Japan. Patients with only mesorectal LN metastasis were classified as the mesorectal-LN group. Patients with lateral pelvic LN metastasis localized to or extending beyond the internal iliac area were classified as the internal lateral pelvic lymph nodes (LPLN) group and external-LPLN group, respectively. Overall survival (OS) and cancer-specific survival (CSS) were compared between the groups.

RESULTS: Lateral pelvic LN dissection was performed in 5789 (50%) of 11,567 patients. Overall, 3905 (34%), 411 (3.6%), and 244 (2.1%) patients were classified as the mesorectal-LN, internal-LPLN, and external-LPLN groups, respectively. When the mesorectal LN group was subdivided as defined by the AJCC, both 5-year OS and CSS were not significantly different between the N2a and internal-LPLN groups (OS: 45% vs 45%, P = 0.9585; CSS: 51% vs 49%, P = 0.5742), and the N2b and external-LPLN groups (OS: 32% vs 29%, P = 0.3342; CSS: 37% vs 34%, P = 0.4347). OS and CSS were significantly better in the external-LPLN group than in stage IV patients who underwent curative resection (OS: 29% vs 24%, P = 0.0240; CSS: 34% vs 27%, P = 0.0117).

CONCLUSIONS: Lateral pelvic LNs can be considered as regional LNs in low rectal cancer, although metastasis extending beyond the internal iliac area is associated with poorer survival.