Combination of ex vivo sentinel lymph node mapping and methylene blue-assisted lymph node dissection in gastric cancer: a prospective and randomized study.

Background: Exact lymph node (LN) staging is crucial for prognosis estimation and treatment stratification in gastric cancer. Recently, a new concept for improving LN harvest and the accuracy of LN staging was introduced. It combines methylene blue-assisted lymph node dissection (MBLND) with a new ex vivo sentinel lymph node (evSLN) mapping technique. The purpose of this study was to investigate these techniques in a prospective and randomized manner.

Methods: A total of 50 patients with proven or suspicious gastric cancer were enrolled. Twenty-five patients each were randomized to the conventional technique (Unstained) or MBLND (Methylene). In 46 cases, additional evSLN mapping with black ink as a marker dye was performed.

Results: Methylene blue-assisted lymph node dissection was associated with a highly significantly improved LN harvest (36 ± 10 vs. 21 ± 10; P < 0.001). The biggest differences were seen in LNs ≤ 6 mm. In contrast to the conventional technique, neither partial gastrectomy nor preoperative chemotherapy influenced LN harvest in the methylene group. The evSLN detection rate, sensitivity, and accuracy were 87, 81, and 93%, respectively. Isolated tumor cells were detected after immunohistochemical staining in 3 of 17 cases (18%). The probability of carrying a metastasis was two times higher in evSLNs compared to non-evSLNs (44 vs. 23%; P < 0.001).

Conclusions: Methylene blue-assisted lymph node dissection is a highly effective method of improving the LN harvest in gastric cancer. Further application of evSLN mapping is feasible and has the potential to heighten the sensitivity of metastasis detection.