Ex vivo lymphatic mapping: a technique to improve pathologic staging in colorectal cancer.

Sentinel lymph node (SLN) biopsy is widely used for solid tumors and has been proposed for use in staging colorectal cancer (CRC). Few studies have examined the ex vivo lymphatic mapping (EVLM) technique for staging CRC. We hypothesized that EVLM is technically feasible, sensitive, accurate, and improves the staging of CRC. After standard resection for colorectal cancer, 1 mL of isosulfan blue dye was injected circumferentially around the tumor. Blue-stained nodes were dissected separately and examined by hematoxylin and eosin (H&E) and immunohistochemical (IHC) stains. Routine pathologic evaluation was performed on all other harvested lymph nodes. Forty patients underwent 43 cancer resections with EVLM from July 2000 to December 2003. SLN were identified in 39 of 43 (91%) specimens. The mean number of SLN obtained was 1.9 (range, 0-5). Pathologic evaluation demonstrated nodal metastasis in 16 of 39 (39%) specimens. The SLN was tumor-positive in 9 of these 16 (56%) patients. The overall accuracy of EVLM was 82%. Two patients (9%) with H&E node negative disease were upstaged when found to have micrometastases by IHC staining. In conclusion, EVLM is technically possible in 90 per cent of patients with CRC. Although overall accuracy was high, the SLN status correlated poorly with the true nodal status of the CRC. However, EVLM improves pathologic staging in 9 per cent of patients and therefore may be of value in CRC.