Patterns of lateral pelvic lymph node metastases and micrometastases for patients with lower rectal cancer

Aims We aimed at investigating the patterns of lymph node metastases and micrometastases in regions of lateral pelvic area, examining circumferential margin involvement and clarifying their prognostic significance. Methods Large tissue slice and tissue array were adopted in the study of 67 patients with AJCC stages I–III lower rectal cancer who underwent total mesorectal excision with systematic lateral pelvic dissection. The outcomes were followed. Results Altogether, 726 lateral lymph nodes were examined, with 32 and 38 were involved by tumor metastases and micrometastases, respectively. Fifty-eight (82.9%) of the involved lymph nodes were smaller than 5 mm. Status of lateral nodes was related to that of mesorectal ones. Middle rectal root (45.5%), internal iliac (31.8%) and obturator (22.7%) regions were more likely to be involved by metastases. Patients with lateral metastases, similar to the group with micrometastases, suffered more recurrence and poorer survival when compared with the ones without metastases. The occurrence of circumferential margin involvement suggested poor prognosis and was related to lateral node status. Conclusions In lateral pelvic area, the majority of lymph nodes harboring tumor were small and could easily be neglected by conventional examination. Incidence of lateral metastases differed among regions, thus more attention should be given to the clearance of the highly occurred areas. More extensive range of dissection and/or adjuvant therapy was recommended for patients with lateral node metastases, micrometastases and circumferential margin involvement, since they predisposed poor prognosis.