Purpose: Lymph node analysis is essential for staging colorectal cancer. Intraoperative lymphatic mapping and sentinel lymphadenectomy remain to be investigated for most gastrointestinal neoplasms. Previous attempts to identify the sentinel node (SN) in solid tumors have used intraoperative techniques. This study describes a novel approach to identify the SN in colorectal cancer using ex vivo lymphatic mapping.
Methods: Eighty-two colorectal cancer patients underwent ex vivo lymphatic mapping and a sentinel lymph node biopsy using isosulfan blue dye following a standard surgical resection between March 2002 and September 2003. Within 5 minutes of resection, colorectal specimens were submucosally injected with isosulfan blue dye in four quadrants. Blue lymphatic channels were identified in the mesentery, and followed to the blue-stained SN(s), which were harvested. The specimens were fixed in formalin and subsequently analyzed in the usual fashion. In patients with T1 or T2 tumors, which were blue-stained nodes, but negative to hematoxylin and eosin staining, were further analyzed by serial section and immunohistochemical staining (IHC).
Results: At least one SN was identified in 79 patients of the 82 patients (96.3%). The average number of SNs identified per patient and nodes in each colorectal cancer specimen were 3 (range, 1～7) and 17.1 (range: 11～47). Thirty five patients had lymph nodes containing a metastatic disease. Thirteen patients had metastases in both sentinel and nonsentinel nodes. There were 7 sentinel lymph nodes as the only site of metastatic disease. In 15 patients the sentinel nodes were negative for disease, whereas the nonsentinel lymph nodes contained a metastatic disease (false negative rate = 42.9%). The false negative rates of SN(s) metastasis in the 26 patients with T1 or T2 tumors were 16.7 and 7.7% by H&E and by serial section and IHC.
Conclusion: Ex vivo mapping of the colon is technically feasible, and may provide a useful approach to evaluate lymph node metastasis in patient with T1 or T2 colorectal cancers.
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