This study reported the length of SB according to tumor characteristics of EGC based on the data from a prospective randomized controlled trial [7]. As far as we know, this is the first report investigating the length of SB based on prospective clinical trial data.
After the effectiveness of SLN biopsy has been validated and proven for the treatment of specific cancers, the SLN biopsy has become the standard procedure in the assessment of metastatic spread to the lymph node basin in breast cancer [12, 13] and malignant melanoma [14, 15]. Unlike conventional SBD which dissects the entire lymph node and its surrounding tissue at a specific basin, SLN biopsy for breast cancer [16] and malignant melanoma [17] is usually performed by picking up each radioactive or dyed lymph node in most cases. On the other hand, there are still concerns about the low accuracy of using SLN biopsy to pick up lymph nodes during gastric cancer surgery, unlike SLN biopsy for breast cancer or melanoma, due to abundant perigastric fat tissue and the limitations of laparoscopic surgery. Regarding this situation, in most trials, SBD was performed instead of conducting an SLN biopsy during gastric cancer surgery [18, 19]. In addition, the SBD procedure has an intention to perform localized lymph node dissection to minimize the possibility of recurrence even in cases with false-negative SLN biopsy results [20]. The SBD procedures that were reported recently are slightly different. In a previous Japanese study, the SBD procedure was defined as the dissection of all the lymph nodes including the SLNs in a particular lymph node station, which was objectively classified in the Japanese Classification of Gastric Carcinoma [21–23]. On the other hand, during the SENORITA trial, we removed only the basin after detecting the extent of the SB [8]. Among these two different methods, there is still no evidence regarding which method is more accurate and appropriate for SBD.
To perform stomach preserving surgery, certain steps in laparoscopic SBD are essential. As previously mentioned, after endoscopic injection of Tc99m-HAS and ICG in the SENORITA trial, tracing is required with a laparoscopy camera and a laparoscopic handheld gamma probe. In addition, after the SBD procedure, an immediate frozen section biopsy examination by pathologists is needed to proceed with the procedure for stomach preservation [7, 9]. In summary, laparoscopic SNNS for stomach preserving surgery requires more additional procedures with longer operation time, endoscopic and pathologic examinations during surgery, and more surgical instruments and manpower compared to the conventional laparoscopic radical gastrectomy for gastric cancer. In our previous report, the median operation time was significantly longer in laparoscopic SNNS (195.0 minutes) compared to laparoscopic conventional gastrectomy (180.0 minutes) per-protocol analysis (P < 0.001) [6]. Therefore, this novel procedure is quite complicated and requires much more preparation for gastrointestinal surgeons to perform. To be a generalized procedure, a simpler and more convenient method for SBD should be developed.
This study began with the hypothesis that since the extent of sentinel lymphatic flow is similar for every patient according to anatomical location, the SBD procedure based on the location of the tumor will also not be different after the tracer is injected. If there is no need for tracer injection and SB detection, the laparoscopic SBD procedure which can be called the localized regional lymphadenectomy around the stomach will be performed more conveniently, and the time of the SBD procedure will be reduced. In addition, there is no need for tracers using radioactive isotopes, which might cause radiation exposure to patients and clinicians, and no need to prepare a fluorescence laparoscopic camera to detect an ICG tracer. In this study, two of the 25 patients were diagnosed with SLN metastasis at intraoperative frozen section biopsy. If the extent of SB can be predicted in advance during surgery, the metastatic SLN can be identified only by SBD procedure with frozen section biopsy, without the procedure of tracer injection and detection. Sequentially, conversion to conventional radical gastrectomy can proceed right after the metastasis at SLNs is confirmed by intraoperative frozen section biopsy.
When the metastasis of SLN can be found without tracer injection during surgery, it is safe from the aspect of oncologic outcomes. The data of this prospective study provide the clinical possibilities of regional lymphadenectomy with an intraoperative evaluation of SLN which can be called D1-lymphadenectomy for EGC. There is no need for tracer injection and SB detection for the frozen biopsy examination of SLN. We can simplify the steps of laparoscopic stomach preserving SNNS. The SBD procedure can be performed even after ESD without the use of a tracer. In addition, by omitting tracer-related procedures, exposure to radioactive isotopes can be avoided, and there is no need to undergo radiation safety management.
The limitations of this study and hypothesis are as follows. First, this study enrolled a small number of patients. Second, the extent or length of SB might be a little different according to the tracer injection site around the tumor by endoscopists. The need for a more accurate protocol for tracer injection sites should be considered. Third, although we could proceed with the SBD without a tracer, a time-consuming intraoperative back table SLN distinction procedure and frozen section biopsy examination for SLNs are still needed. In addition, we need the procedure to localize the tumor during laparoscopic surgery such as intraoperative endoscopy. Lastly, it is possible for surgeons to describe the longitudinal location of the tumor based on the site of the gastric angle. On the other hand, it is difficult to describe the exact circumferential location of the tumor due to the lack of gastric landmarks. Even when the circumferential location of the tumor is ambiguous, we suggest that the surgeons dissect the SBs at both the lesser and greater curvature side of the stomach from the reference point to proximal or distal SB margins. In considering the blood supply at the SBD site around the stomach, either a gastric wedge or segmental resection is recommended instead of endoscopic submucosal dissection due to the risk of delayed perforation by reduced blood supply [24]. Nevertheless, it is expected that the present prospectively collected data of SB extent could be a draft for simplifying laparoscopic SNNS.
We reported values of 3.4 ± 0.9 cm proximally and 3.2 ± 0.8 cm distally for the length of the SB along the LC, and values of 7.0 ± 1.9 cm proximally and 6.5 ± 1.7 cm distally for the length of the SB along the GC of the stomach. The length of the SB presented in this study could be a reference for identifying the extent of the SB without the use of tracers. It may simplify the complicated and time-consuming procedures of laparoscopic SNNS for stomach preservation in EGC.