What factors affect lymph node yield in surgery for rectal cancer?

OBJECTIVE: The detection of lymph node metastases is of vital importance in patients undergoing excisional surgery for rectal cancer as it provides important prognostic information and facilitates decision-making with regards to adjuvant therapy. It has been suggested that patients in whom only a small number of nodes are present in the excised specimen have a worse prognosis, presumably due to inadequate lymphadenectomy and consequent understaging of the disease. The aim of this study was to determine which factors affect the yield of lymph nodes. METHODS: This was a retrospective study of patients who had undergone a resection for histologically proven adenocarcinoma of the rectum. The total number of lymph nodes identified in the excised specimen was recorded in each case. A multivariate analysis was performed to ascertain whether this number was significantly influenced by any of several variables. RESULTS: A total of 167 patients were studied (M:F ratio 107 : 60, median age 70 years). The median number of lymph nodes contained within the resected specimen was 16 (interquartile range 10-21). On univariate analysis a significantly higher yield of lymph nodes was obtained with tumours in the middle third of the rectum (P=0.007), larger tumours (P < 0.001), more locally advanced tumours according to both pT staging (P=0.001) and Dukes' staging (P=0.020), an increased number of involved nodes (P=0.003) and examination by a specialist histopathologist (P=0.003). On multivariate analysis the only significant variables were tumour size (P=0.021), number of positive nodes (P=0.007) and histopathologist (P=0.021). CONCLUSIONS: The number of lymph nodes identified within the excised specimen in patients undergoing resection of a rectal cancer positively correlates with the size of the tumour and is also dependent on the examining histopathologist. In addition, in node-positive patients the number of involved nodes increases with increasing lymph node yield.