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Blue or green dyes are also injected in the submucosal layer at primary lesion in a similar manner right
after surgery began. Blue- or green-stained lymphatic vessels as well as lymph nodes are visualized during
laparoscopic observation within 15 min after the injection. A hand-held gamma detector is also useful to
locate the radioactive SN accurately. Moreover, laparoscopic gamma probing is feasible using a gamma
detector which is available via trocar ports [10,11] .

For intraoperative SN biopsy, the pickup method is commonly employed in breast cancer and melanoma.
However, the intraoperative SN sampling for gastric cancer should be accompanied with sentinel lymphatic
basin dissection, which is a selected lymphatic basin dissection including identified SN [10,11] . The lymphatic
basins around the stomach are currently divided into five basins along the main gastric arteries: basins along
left gastric artery, right gastric artery, left gastroepiploic artery, right gastroepiploic artery, and posterior
gastric artery .
[12]
ICG has excitation and fluorescence wavelengths in the near-infrared range . Many studies have clearly
[13]
demonstrated the clinical utility of intraoperative ICG infrared imaging for laparoscopic SN mapping using
infrared ray electronic endoscopy (IREE) to date [13,14] . IREE is useful to visualize ICG-stained lymphatic
vessels and SN more clearly than normal laparoscopy. Subsequently, ICG fluorescence imaging was also
developed as a reliable novel technique for SN mapping [15,16] . SN can be clearly visualized using laparoscopic
ICG fluorescence imaging in comparison with conventional normal light imaging. Although the efficacy of
ICG infrared or fluorescence imaging should be carefully evaluated by further prospective studies regarding
SN detection rate and accuracy to predict the nodal metastasis, and compared with radio-guided methods,
the new technologies may markedly improve the accuracy of laparoscopic SN mapping and biopsy in early-
stage gastric cancer.

FEASIBILITY OF SN MAPPING IN GASTRIC CANCER
Until now, approximately 100 single institutional studies of SN mapping have indicated favorable SN
detection rate and accuracy to predict nodal metastasis for early-stage gastric cancer. These results are as
good as those of SN mapping for breast cancer and melanoma . A meta-analysis, which consisted of 38
[11]
SN mapping studies including 2128 patients with gastric cancer, showed that the SN detection rate and
accuracy of nodal status determination were 94% and 92%, respectively . The study also indicated that SN
[17]
mapping for gastric cancer is reliable especially in patients with T1 tumor, use of dual tracers and submucosal
injections of tracers.

A Japanese group previously conducted a prospective multicenter trial (UMIN ID: 000000476) to evaluate
the feasibility of SN mapping for gastric cancer using the dual tracer method . In this study, SN mapping
[10]
and biopsy were performed for 397 patients with cT1N0M0 or cT2N0M0 single tumor with primary lesion
diameter of < 4 cm and those without any previous treatment. To estimate the accuracy of the SN mapping,
D2 or modified D2 gastrectomy was essentially performed for enrolled patients after SN mapping according
to the guidelines for standard care by The Japan Gastric Cancer Association.

As the results of the study, the SN detection rate was 97.5% (387 of 397), and 14.7% of patients (57 of 387)
showed lymph node metastasis. Fifty-three (93.0%) of the 57 patients with nodal metastasis showed positive
SN for metastasis. False-negative rate was 7% (4 of 57), and the overall accuracy to determine nodal metastatic
status based on SN mapping was 99.0% (383 of 387). Of the 53 patients with positive SN, 32 (60.4%) had nodal
metastases limited to only SN. Of the 21 SN-positive/non-SN-positive patients, 15 (71.4%) had metastatic
non-SN located within SN basins and 6 (28.6%) had metastatic non-SN located outside the SN basins but
within the extent of the D2 lymphadenectomy. Of the 4 patients with false-negative SN biopsy, 3 patients
had either primary tumors of more than 4-cm diameter or pT2 tumor or both, and only 1 patient who