Comparison of ex vivo and in vivo injection of blue dye in sentinel lymph node mapping for colorectal cancer.

Background: The technique of sentinel lymph node (SLN) mapping in patients with colorectal cancer varies between reports, and the optimal method has not been established. The purpose of this study was to determine the optimal injection technique for SLN mapping.

Methods: Sixty-nine consecutive patients who underwent curative surgery for colorectal cancer were enrolled. The SLNs was identified intraoperatively by subserosal blue dye injection (in vivo) or by submucosal injection after standard colectomy (ex vivo). If negative by conventional hematoxylin and eosin staining analysis, all lymph nodes, SLNs and non-SLNs, were subjected to further analysis by multi-level section and immunohistochemical examination.

Results: The in vivo and ex vivo injected groups were similar in demographic character, tumor size, and histological grade. The mean number of SLNs identified was 2.3 in the in vivo group and 2.6 in the ex vivo group (p = 0.192). The detection rate of SLNs by blue dye injection was somewhat higher in the ex vivo group than in the in vivo group: 90.6 vs. 81.1% (p = 0.219). The false-negative rate was 23.5% for the in vivo group and 13.3% for the ex vivo group (p = 0.392). The upstaging rate, which was 18.5% overall, was similar in both groups (p = 0.538).

Conclusions: These findings suggest that ex vivo blue dye injection is an effective alternative to in vivo injection for identifying SLNs in patients with colorectal cancer. Because of its simplicity and applicability in routine clinical settings, further investigation of the ex vivo mapping technique is warranted.