Most cases of MLBO are advanced, having a depth of wall invasion deeper than T3, with vascular invasion and positive lymph nodes [7, 21, 22]. There are also some reports that 25% of MLBOs are diagnosed as Stage IV, which indicates distant metastases . There is also a report that the long-term prognosis is equivalent to non-obstructed cases when compared by stage , but even in the same stage, many cases of MLBO are reported to be advanced cases and to have poorer prognosis . Therefore, patients with stage II MLBO are considered the so-called high-risk group, for which postoperative adjuvant chemotherapy is recommended in the guidelines.
In this retrospective study, we examined the short- and long-term prognoses of MLBO to verify the effectiveness and safety of the BTS strategy using SEMS. Although no direct comparison with emergency surgery was made in this study, no significant difference in either short-term or long-term prognosis of colorectal cancers has been reported in the past. Furthermore, the BTS strategy secures time for systemic examination such as for the presence of multiple cancers. Therefore, we consider SEMS placement to be an effective treatment strategy for MLBO.
At present, there is no consensus on the effectiveness of SEMS for BTS in MLBO. The ESGE guidelines emphasizes the limitation that SEMS as a BTS should be considered within sufficient skill and expertise . Sensitivity analysis at a meta-analysis study concluded as experience and quantity affect long-term outcome from the result of a technical success rate of 90% vs. 90% or experience of SEMS cases of <40 vs. ≥40 . This study also revealed that a perforation rate of less than 8% had significantly better 3-year overall survival than studies with a perforation rate of 8% or more. As perforation is reported to be one of the risks of peritoneal dissemination and a poor prognostic factor , the success rate of SEMS placement would seem to affect the long-term prognosis. The success rates shown in the cohort studies conducted in Japan were 98–99% with low perforation rates of 0–2%. In the present study as well, only 2 of the 75 patients suffered perforation, and the technical success rate was high at 97.3%, which indicates that SEMS placement could be safely performed. In addition, there is a report that mechanical compression of a tumor with a metallic stent induces perineural invasion and stimulates cancer cells to promote tumor growth and metastasis , whereas other reports found no significant difference in perineural invasion compared with a transanal tube. Another report concluded that mechanical compression of the tumor rather decreased the proliferative capacity . Therefore, the effect of metallic stents on long-term prognosis still remains controversial and an important topic. A multicenter randomized controlled trial (COBRA trial) is currently underway in Japan to establish its own evidence. In our institution, SEMS is widely used as a BTS for MLBO on the basis of these results. Table 5 shows the strategy in our institution. The point to be noted in this strategy is that considering emergency surgery including temporary stoma construction rather than SEMS placement in cases of invasion of the other organs (depending on the organs) and in lower rectal cases. However, as shown in the schema, due to reasons of securing the margin for resection and the pain involved after insertion, a transanal ileus tube or emergency surgery is rather recommended for lower rectal cancers (Table 5). The indication of the laparoscopic approach is also problematic in advanced cases of MLBO after SEMS placement. While some reports showed the feasibility and safety of laparoscopic surgery after SEMS placement with no transition to open surgery and fewer complications, no reports suggested for long-term prognosis [29, 30]. We also compared laparoscopic surgery and open surgery in this study.
In recent years, the development of surgical devices and endoscopic surgical techniques has led to the widespread use of laparoscopic surgery even for advanced colorectal cancers. However, there is no consensus on a surgical approach for MLBO, especially with colonic stent placement. Law et al  compared short-term treatment after colonic stent placement between open and laparoscopic surgery groups and found that the postoperative hospital stay was shorter and the incidence of postoperative complications was lower in the laparoscopic surgery group. Other reports on BTS also showed that laparoscopic surgery tended to be performed on patients in whom effective decompression was achieved . In the early stage of BTS, we performed the operation by laparotomy, but laparoscopic surgery has gradually increased over time and is presently the first choice. However, we still perform laparotomy in patients with T4b cancer.
Although the incidence of anastomotic leakage was somewhat high in the Lap group in the present study, there was no complication higher than Clavien-Dindo grade 3b that required reoperation. For this reason, left-sided colorectal cases (including RS, Ra, Rb) tended to be included in the Lap group.
Regarding long-term prognosis in the study patients, 3-year OS was over 80% for all stages, and there was no significant difference between open and laparoscopic surgery. These results suggest that the combination of SEMS placement with laparoscopic surgery may be a feasible and safe treatment.
In patients with colorectal cancer, the prevalence of synchronous cancers ranges from 0.7% to about 7% [33, 34]. However, synchronous multiple cancers were detected in 14.7% of patients in our institution. Therefore, we perform total colonoscopy including the oral side of the primary tumor in our institution before performing BTS to avoid an unnecessary second colorectal resection.
As the limitations, this is a retrospective, single-arm study and should better to be compared by factors such as tumor localization and postoperative treatment which may affect RFS and OS. Moreover, since this study does not compare the primary anastomosis case with the stoma construction case, it is difficult to concluded that the stoma construction can be safely avoided.