There was a significant correlation between the presence of PI and lymph node metastasis. Those who were PI-positive also had a significantly lower 5-year DSS rate. However, there was no correlation between the presence of PI and tumor location.
There was a significant difference in the 5-year DSS rate among those with T2a and T2b tumors. In the PI-positive group, radical cholecystectomies led to a higher 5-year DSS rate than simple cholecystectomies (57% vs 25%, p = 0.04); however, different surgical procedures had no significant effect on the PI-negative group.
Surgery is the only treatment found to be effective against GBC. For patients whose tumors have reached the depth of the mucosa (m) or muscularis propria (mp), a cholecystectomy is an adequate procedure [6]. However, when tumor invasion reaches the subserosal (ss) level, approximately 50% of patients develop lymph node metastases [6–8], and cholecystectomy is insufficient. Therefore, the preoperative diagnosis of ss invasion is important to determine the required surgical procedure.
Transabdominal US and CT scans are the primary methods used for GBC detection. However, because GBC visibility on US is influenced by the physical status of the patient, endoscopic ultrasonography (EUS) of the upper gastrointestinal tract is the gold standard for the preoperative diagnosis of GBC [18, 19]. Sugimoto et al. [20] developed a simple method for diagnosing ss GBC; however, its accuracy was influenced by the tumor location and condition as well as the technique of the endoscopist. Iwashita Y. et al. [21] reported that assessment of irregular vessels on the gallbladder wall might be useful for detection of subserosal infiltration using by laparoscopic narrow band imaging. Thus, new safe and reliable devices for more precise diagnoses are needed.
In general, T2 GBC with lymph node metastasis shows poor prognoses, and regional lymph node dissection is recommended [6, 7, 22]. Kishi et al. also recommend lymph node resection to the posterosuperior pancreatic head and along the hepatoduodenal ligament and hepatic artery [23].
Our data indicated that the PI-positive group had statistically lower 5-year DSS and that PI was correlated with lymph node metastasis. This indicates that the PI-positive group required radical cholecystectomies due to the high risk of lymph node metastases. No statistical difference was observed in the 5-year DSS between PI-negative patients who underwent radical cholecystectomies and those who underwent simple cholecystectomies. These results indicated the importance of preoperative diagnosis and postoperative histological diagnosis. In our institute, those with postoperative histological verification of PI-positive group underwent regional lymph node dissection within 2 months of the first operation.
Our data also revealed favorable 5-year DSS rates in PI-negative pT2 GBC patients. If a PI could be clearly identified before the operation, radical cholecystectomy may be avoided, and the burden on the patient will be reduced, even in pT2 GBC patients. Similarly, if intraoperative diagnosis of PI were possible, we could change the surgical strategy from simple to radical cholecystectomy. Recently, laparoscopic radical cholecystectomies have increased alongside an increasing amount of evidence for their oncological safety [11–14]. A recent paper has found that hepatectomies may not be required in T2 GBC if the preoperative evaluation confirms the depth of the tumor to be in the ss layer [15]. New methods for the diagnosis of PI preoperatively or intraoperatively are required. Once these become available, they will alter the surgical strategies used.
Our study had some limitations. First, this was a retrospective study that included a small number of cases. Second, the rate of lymph node metastases in our sample was very low, because some patients only underwent simple cholecystectomy, which precluded the determination of precise lymph node metastases rates. However, while there have been many reports on the lymph node metastases rate in pT2 GBC, few papers have looked at the effect of PI on survival rates.