Most of the studies on obstructive CRC report on the comparison with non-obstructive CRC and the efficacy of SEMS as BTS; there are few analyses on the prognostic factors of obstructive CRC. For BTS, there is no difference between decompression using temporary stoma and SEMS ; many recent reports and meta-analyses show no difference in long-term outcomes between BTS using SEMS and emergency surgery [10, 12, 25]. Regarding BTS using TADT, retrospective studies, which are small in size and mostly from Japan, show no difference from BTS using SEMS .
As prognostic factors for obstructive CRC, ASA-PS, serum albumin level < 4.0g/dL, and depth of invasion T4 and R1 resection (cancer positive at cut-end) have been reported to be independent risk factors for recurrence . In a comparative study between emergency surgery and BTS using SEMS, age, ASA-PS, depth of invasion, and lymph node metastasis were prognostic factors for disease-free survival . A report from Japan, which is a study of 50 cases of emergency surgery and 50 cases of BTS using SEMS for Stage II/III obstructive CRC, showed that BTS and venous invasion were poor prognostic factors for RFS; BTS and T4 depth of invasion were poor prognostic factors for overall survival (OS) . Long-term outcomes (OS and disease-free survival (DFS)) of emergency surgery and BTS using SEMS were equivalent, but NLR was a prognostic factor for DFS in emergency surgery. Additionally, lymphocyte-monocyte ratio was a prognostic factor for OS and DFS of BTS using SEMS, as well as for OS in emergency surgery and BTS using SEMS . Furthermore, a study of BTS cases using SEMS and TADT showed differences only in T4 depth of invasion and the Controlling Nutritional Status (CONUT) score for DFS, with no differences in lymph node metastasis or adjuvant chemotherapy .
As mentioned above, for obstructive CRC, lymph node metastasis, which is a popular prognostic factor, is not often selected. This may be due to the fact that many reports on prognostic factors for obstructive CRC were based on a small number of cases, as well as to stage migration due to inadequate lymph nodes dissection or a small number of harvested lymph node in emergency surgery. Furthermore, in Stage II CRC, colonic obstruction is considered an independent poor prognostic factor , which may weaken the impact of other prognostic factors.
In the analysis of all patients enrolled in this study, depth of invasion and postoperative complications were selected as prognostic factors; lymph node metastasis was not selected. When only Stage III cases were included, adjuvant chemotherapy was selected as a prognostic factor. Therefore, in order to exclude the possibility of stage migration due to insufficient lymph node dissection, we excluded patients with < 12 harvested lymph nodes in Stage II. Lymph node metastasis was found to be a prognostic factor in patients with a sufficient number of harvested lymph nodes. In Cox’s multivariate analysis, depth of invasion, lymph node metastasis, and adjuvant chemotherapy were also selected as independent prognostic factors. The number of cases with < 12 harvested lymph nodes were significantly higher in patients undergoing emergency surgery, which may be due to insufficient lymph node dissection because of general condition or bowel dilatation, or insufficient lymph nodes collection from the resected specimen after surgery. In Japan, it is the surgeon’s job to collect the lymph nodes from the resected specimen; this work may have been inadequate during emergency surgery, which is often performed after hours. Furthermore, it is important to consider that patients who underestimated their stage due to having < 12 harvested lymph nodes may have been disadvantaged because they should have received adjuvant chemotherapy. In addition, preoperative CEA, CA 19 − 9 and NLR, which are generally considered to be prognostic factors, were not selected as prognostic factors in this study.
For this study, the following limitations should be considered. First, this study is that it was not designed to analyze the prognostic factors of obstructive CRC, but as a post-hoc analysis of a retrospective multicenter study to analyze the comparison of survival and perioperative outcomes of BTS using SEMS, TADT, and emergency surgery for LOCRC; there are cases with missing data. Second, patients who died as a consequence of SEMS placement and TADT placement remained beyond the scope of the present study. However, as no postoperative deaths after SEMS placement have been reported in any previous reporting on SEMS as BTS, the influence of this shortcoming is expected to be negligible. Third, long-term outcome was assessed by the RFS as a primary endpoint in this study. Due to the significant advances in therapeutic chemotherapy in recent years, we believe that there would be only small difference in long-term outcome based on the overall survival.