OBJECTIVETo evaluate the feasibility and utility of an ex vivo sentinel lymph node (SLN) identification and ultrastaging for colorectal cancer (CRC).

METHODSCRC patients undergoing resection of a primary colorectal cancer were considered for inclusion. Following resection, SLN identification was performed. The SLN was dissected from the mesentery and submitted separately for pathologic analysis. All lymph nodes were stained with HE. Blue lymph nodes, when negative by routine HE staining, were further analyzed.

RESULTSA total of 62 tumors from 60 patients with colorectal cancer were studied. 95.2% (59/62) specimens was successfully identified. In these 59 specimens, a total of 1114 (18.9 per specimens) lymph nodes were examined; of these, 157 (14.9%) were designated as SLNs. The number of blue-stained lymph nodes removed ranged from 1 to 9, with a mean of 2.7 blue nodes identified. The sensitivity of a blue-stained lymph node identifying metastatic disease was 39.1%. The false-negative was 23.7%. In 4 specimens micrometastases were detected only by immunohistochemistry with cytokeratin.

CONCLUSIONSEx vivo sentinel lymph nodes mapping in colorectal cancer is feasible and can identify the SLNs with a very high success rate. Ex vivo SLN mapping improves pathologic staging of patients with CRC. The SLN evaluation should not replace attempts to harvest large number of nodes for standard processing. SLN mapping can help improving the number of nodes for pathological examination.