Gastric cancer is the fifth most frequently diagnosed cancer and the fourth leading cause of death from cancer worldwide (1). Composing complete removal of the tumor and systemic lymph node (LN) dissection, radical surgery remains the mainstay frontline treatment for resectable gastric cancer (2–4). Adequate assessment of the lymph nodes is essential for its role in the disease stage and its prognostic value (5–10), and D2 lymphadenectomy is recommended for advanced gastric cancer (2–4, 11–13).

Laparoscopic gastrectomy (LG) was first reported by Kitano (14) in 1994 and applied in the treatment of advanced gastric cancer by Goh (15) in 1997. Possessing the advantages of minimal invasion and quick postoperative recovery, LG is gradually replacing open surgery as the first choice (16–19). However, because of the lack of tactile feedback and direct observation compared with open surgery, precise tumor positioning under laparoscopy is relatively difficult, especially for patients with early gastric cancer not invading the serosa and those who need additional surgery after noncurative ESD. In addition, the complexity and vastness of the layout of blood and lymphatic vessels contribute to the difficulty and risk of effective LN dissection. Decision and evaluation making done only by the means of surgeons’ experience is extremely subjective and poses a danger of false negativity, which may cause insufficient LN dissection and poor prognosis of patients.

As a new surgery technology, dye-mediated surgical navigation (including carbon nanoparticles, indocyanine green, etc.) proved to supply surgeons with improved inspection of the complex perigastric anatomy during laparoscopic surgery. Studies have shown that carbon nanoparticle lymphatic mapping technology increases the number of LNs harvested and realizes tumor localization (20–22). Drawbacks exist, however, that once the carbon nanoparticles leaked into the abdominal cavity, the whole surgical field would be dyed black, thus interfering with the vision of the surgery field and increasing operation difficulty.

Approved by the US Food and Drug Administration (FDA) in the 1960s, ICG was applied to assess cardiac output and hepatic function in the early stage (23–26). Possessing the advantages of not interfering with the surgical field and high tissue penetration (27, 28), ICG fluorescence-guided laparoscopic surgery is therefore the subject of numerous studies (29–34). At present, the application of ICG in LRG has achieved certain success (35, 36) (37, 38). When injected into the gastric tissue around the tumor with endoscopy and exposed to a specific wavelength of near-infrared light, fluorescence emitted from ICG displays the tumor and perigastric LNs (39), making them visible and facilitating the surgery.

To further investigate the feasibility and safety of ICG fluorescence technology in LRG and provide valuable medicine evidence for clinical decision-making in radical gastric cancer resection, we conducted this retrospective study by evaluating the role of ICG fluorescence technology in surgical procedures, lymph node dissection, short-term survival, etc.

One hundred ninety-five patients (107 patients in the ICG group and 88 patients in the control group) were retrospectively analyzed. No significant differences were observed in sex, age, BMI, ASA score, or ECOG performance status between the two groups (P > 0.05), which indicates that the baseline characteristics of the two groups were comparable. ( Table 1 )

Recently, with the widespread application of laparoscopic surgery for patients with gastric cancer, ICG fluorescence-guided LRG has attracted much attention as a novel navigation technology. To evaluate the feasibility and safety of ICG in LRG, this study was conducted and indicated that compared with conventional LRG, ICG-guided LRG has the advantages of more lymph nodes dissected, less blood loss, and shorter operation time.

As a crucial step in gastric cancer surgery, adequate resection and assessment of LNs have been shown to be linked to disease staging, regional disease control, and long-term survival (6, 7, 44). Interestingly, fluorescence observation based on the absorption characteristics of ICG has been reported to make it possible to distinguish LNs containing ICG particles from surrounding tissue (45, 46), improving the chance of complete dissection. Kwon et al. (47) reported that ICG fluorescence-guided lymphography offered increased lymph node retrieval compared with conventional laparoscopic surgery. Chen et al. (48) suggested that more lymph nodes could be harvested during ICG-guided LRG with decreased lymph node noncompliance. Similar results are reported in this study; likewise, some new and interesting findings are yielded.

For example, the splenic artery may turn, twist, and become tortuous after originating from the celiac trunk, leading to the obscuration and difficulty of 11P LN dissection. However, possessing the property of strong tissue penetration, ICG fluorescence may highlight lymph nodes and enable the retrieval of a higher number of lymph nodes. In addition, because of the different diffusion and uptake rates of ICG in different tissues, perigastric blood vessels and associated lymphatic vessels can be accurately distinguished, making it possible to remove more lymph nodes adjacent to the blood vessel. Especially in the splenic hilum area, the relatively narrow operating space, the complexity of the vascular anatomy and the fragile texture of the spleen make ICG an indispensable tool to improve the safety and accuracy of surgery.

Since 1997, the Union for International Cancer Control (UICC) and American Joint Commission for Cancer (AJCC) have adopted the N stage of the tumor, node, metastasis (TNM) classification based on the number of metastatic lymph nodes (49). In our study, it seems that there were sufficient lymph nodes in the control group for positive lymph node status determination and more lymph nodes in the ICG group were unnecessary, but we should not ignore the fact that lymph node micrometastasis could not be exactly evaluated by routine H&E examination and is well associated with poor outcome in patients (50–54). Huang et al. (55) demonstrated that the number of dissected LNs is the only factor affecting negative lymph node counts. In other words, more lymph nodes dissected increases the number of positive lymph nodes and so-called negative nodes that may harbor micrometastases, thus leading to a better prognosis (56–58).

Although our study found that more overall LNs contributed to more positive LNs in the ICG group, we should take it into account that ICG is not a targeting marker for tumor cells (59) and is unable to trace positive LNs specifically. We also conducted a small sample (35 patients) study examining fluorescent and nonfluorescent LNs respectively in the ICG group, and no significant difference was found in the metastatic rate confirmed by pathology. Moreover, it is not uncommon to find discrepancies in which some obviously enlarged LNs are proven to be pathologically metastatic, but they are not fluorescent (60). This is considered to be partly because the lymphatic vessels were obstructed by a massive cancer embolus, the ICG cannot flow into these LNs (61). Therefore, ICG fluorescence technology can only be used to assist lymph node dissection, instead of being relied on to determine whether the lymph node is metastatic, which is consistent with the report of Cianchi et al. (62)

Another key step in curative gastric cancer surgery is the complete removal of the primary tumor with sufficient negative margins. Indeed, positive margins are associated with significantly worse survival (63–65). In fact, ICG fluorescence can improve the lack of visual inspection and palpation in traditional laparoscopic surgery and prove effective in the identification of tumors in our study. The surgeon can observe the tumor with frequent switching between white light view and near-infrared mode after endoscopic ICG injection around the tumor. As a consequence, it is possible to reduce the operation time and surgical invasion. In addition, the characteristics of ICG in distinguishing lymph nodes and surrounding tissues also enable prompt and accurate intraoperative decisions to speed up the surgical process and reduce the risk of blood vessel injury and bleeding.

It is reported that intraoperative blood loss and transfusion are associated with a higher risk of morbidity and mortality, although further investigation is needed (66–69). Yasuda et al. reported that not only the volume of blood loss, but the operation time is associated with morbidity after gastrectomy (70). In addition, cardiopulmonary adverse effects of general anesthesia and dioxide pneumoperitoneum are significant in laparoscopic surgery (71, 72). In this study, the ICG group was shown to provide the advantages of decreased intraoperative blood loss and shorter surgery time than the control group. The routine use of ICG fluorescence could potentially reduce the perioperative complications caused by blood loss and prolong dioxide pneumoperitoneum during LRG. In addition, the morbidity rates were 14.0% in the ICG group and 13.6% in the control group (P>0.05), which were similar to the rates reported in previous studies (73, 74). No intraoperative events or delayed complications during their hospital stay related to ICG were observed.

After a 2-year follow-up, there was no significant difference in long-term survival in each stage between the ICG group and the control group. This may be explained by the fact of the shorter follow up period of the present study. We also found that ICG-guided LRG obviously improved OS and DFS, because the number of harvested LNs in the ICG group was significantly larger and adequate numbers of LNs dissected in the standard lymphadenectomy region were necessary for accurate disease staging and avoiding LN micrometastasis, thus having a good impact on the prognosis of patients (75–77).

Currently, two ICG injection methods are used: preoperative endoscopic submucosal injection and intraoperative subserous injection. During the study, we found that the former is superior (61) since intraoperative injection may increase surgery risk caused by prolonged operation time and pneumoperitoneum time. In addition, the location of the tumor cannot be indicated accurately under laparoscopy if ICG was not injected around the tumor (78). There was also not sufficient time for ICG to diffuse from injection sites into the D2 station LNs. Of note, the concentration of ICG solution should not be too high; otherwise, the excessively strong fluorescence intensity may obstruct the observation of tissues. However, unlike carbon nanoparticles, low-dose of ICG is not visible in white light mode, so high concentrations or leakage of ICG do not interfere with the surgeon’s vision.

There are some limitations to this study. First, compared with the control group, patients in ICG group had to bear more costs for indocyanine green and endoscopic injection. Second, there was no significant difference in long-term survival between the two groups due to the relatively short follow-up time, so a longer follow-up is necessary. Third, ICG is not a targeting tracer for tumor cells, so efforts to develop more targeted dyes are required. Fourth, this was not a strictly randomized controlled study, but patients almost randomly accept endoscopic ICG injections. The study was conducted at Qilu hospital of Shandong university that performs more than 1,000 gastrectomies for advanced gastric cancer each year. Considering the large number of patients, relatively few inpatient beds and the cost of hospitalization, the number of days in hospital before surgery was strictly controlled. In our hospital, gastroenterologists are also endoscopists, who are mainly responsible for the treatment of patients in addition to endoscopy. Inpatients waiting for surgery can receive endoscopic injection only after completing all preoperative examinations and making a successful appointment with an endoscopist. Those who do not meet these requirements cannot receive ICG injection.

In summary, a large randomized, multicenter trial is warranted to further evaluate the feasibility and safety of indocyanine green fluorescence technology in LRG for gastric cancer.

This study indicates that, with a shorter operation time, less blood loss, and no complications attributable to ICG, ICG fluorescence technology can guide surgeons to rapidly locate tumors and harvest more lymph nodes than conventional LRG. In addition, the two-year OS and DFS are comparable between two groups. In conclusion, ICG fluorescence technology in laparoscopic radical gastrectomy is safe and valuable.

WY is the corresponding author. MW and YZ are joint first authors. WY contributed to the study concept and design. WY, ZB and MW conducted the laparoscopic radical gastrectomy. LM and ZL conducted the endoscopy. MW and YZ wrote the manuscript. MW, YZ, LM, ZL, YY, ZB, DP, YD, XZ and PL conducted the data collection and analysis. WY revised and edited the manuscript. WY and YY are the guarantors of this study. All authors contributed to the article and approved the submitted version.

The raw data supporting the conclusions of this article will be made available by the authors, without undue reservation.

The studies involving human participants were reviewed and approved by the Medical Ethics Committee of Qilu Hospital of Shandong University. The patients/participants provided their written informed consent to participate in this study.

This work was supported by the Natural Science Foundation of Shandong Province, China (Grant/Award Number: ZR2019LZL006) and the Horizontal Project of Shandong University (Clinical Study of Intraoperative NIR Application—Clinical Study of ICG-labeled Fluorescent Laparoscopic Technique in Total Laparoscopic Radical Gastrectomy; Grant/Award Number: 6010119083).

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.