Methylene blue ex vivo staining of resected colorectal cancer specimens to enhance lymph node retrieval: a randomised controlled trial

INTRODUCTION. Metastatic involvement of regional lymph nodes is a major prognostic factor of colorectal cancer inf luencing treatment strategy. An international consensus standard requires retrieval of at least 12 lymph nodes from resected colorectal specimens. The aim of the present study was to assess the effect of staining colorectal specimens with intra‐arterial methylene blue for the lymph node yield. MATERIALS AND METHODS. In a two‐year period 236 consecutive radically operated colorectal cancer patients were randomised into methylene blue staining and non‐staining groups. Fifteen ml of methylene blue was injected intra‐arterially in the operating room after specimen removal. After formalin fixation colorectal specimens were analysed for retrieved lymph node count, diameter and metastatic involvement. RESULTS. The intervention and control groups were homogeneous in terms of patient characteristics. There was a significant difference in the number of retrieved lymph nodes. Mean number of lymph nodes was 16 (95% CI 14‐19) in the non‐stained and 30 (95% CI 26‐31%) in the stained group (p < 0.001). There was also a significant difference in finding 12 and more lymph nodes (93% in the stained and 70% in the non‐stained group, p < 0.0001). In the stained group more small‐diameter (<= 4 mm) lymph nodes were found and examined (22.5 vs. 10 p < 0.0001). In the stained group 33% of the patients and in the non‐stained group 25% of the patients (NS) had metastatic involvement only in the small lymph nodes. In subgroup analysis of rectal cancer patients who received neoadjuvant radiotherapy, 12 and more lymph nodes were found in 78% of the patients of the stained group and in 50% of the patients in the non‐stained group (p = 0.026). However, as there was no significant difference in the rate of patients in metastatic involvement of the lymph nodes between the groups, no upstaging effect occurred in the stained group. CONCLUSIONS. Methylene blue staining is a simple procedure which enables to find more small lymph nodes and therefore significantly improves the lymph node yield. The method is particularly helpful in patients on receiving neoadjuvant therapy in whom lymph node count without staining would be low.