Potential tumor spread of lateral pelvic lymphatic flow in low rectal cancer

In Japan lateral pelvic lymph node dissection has been actively performed with total mesorectal excision for low rectal cancer. However, its definitive efficacy remains unclear. This study is to evaluate clinical significance of lateral pelvic lymphatic drainage in low rectal cancer patients by 99mTc-Sn colloid radioactive tracers.

Intraoperatively detecting rectal lymphatic drainage using 99mTc-Sn colloid radioactive tracer in 39 low rectal cancer patients, we performed lateral pelvic lymph node dissection in lateral pelvic lymphatic flow-positive patients.

Lateral pelvic lymphatic flow was detected in 11 patients (28%). In four (36%) of 11 patients, tumor cells were histologically identified in lateral pelvic lymph nodes. A median size of metastatic lateral pelvic lymph nodes was 7.5 (range, 2-150) mm, and all but one overlooked patient could not be detected by routine preoperative imaging scans retrospectively. The five-year disease-free survival rate of lateral pelvic lymphatic flow-positive patients was significantly poorer (45% vs. 75%, p = 0.0044).

Tumor cells potentially extended beyond the fascia propria recti in low rectal cancer with lateral pelvic lymphatic flow. Preoperative chemoradiation therapy and adjuvant therapy are considered to be reasonable to improve a poor prognosis of low rectal cancer patients with lateral pelvic lymphatic flow.