Rectal cancer surgery is frequently associated with complications.[15-17] Defecation disorders are among the most frequent complications after rectal cancer surgery. The Japanse treatment guidelines recommend total mesorectal excision for patients with rectal cancer. In addition, we are also actively working on lateral lymph node dissection and ISR to prevent local recurrences. These surgical treatments cause bowel dysfunction due to damage of the anal sphincter muscle and a reduction in rectal volume.[19-21] On the other hand, preoperative radiation therapy is recommended for patients with advanced rectal cancer in Western countries, and it has been reported that the radiation therapy also leads to defecation disorders.[13, 22] The incidence of major LARS after rectal cancer surgery has been reported to be more than 40% [22-24], and the incidence of major LARS was similar in this study.
Defecation disorders impose limits on daily life activities and mental stress.[25, 26] It is considered necessary to treat or prevent defectation disorders after rectal cancer surgery. One study reported that sacral nerve stimulation therapy could effectively alleviate defection disorders. However, there has been no evidence of an effective treatment for LARS. Recently, it has been reported that a nomogram may be effective in preventing complications.[28, 29] In addition, the nomogram may be beneficial for counseling patients. Therefore, we expect that our nomogram can play an important role for LARS therapy.
We identified three predictive factors for major LARS: male, age, and tumors location. These factors were also identified as predictors of defecation disorders in other reports. A feature of the characteristics of the nomogram, the influence of each factor can be visualized, and as shown in Fig. 2, it can be seen that the distance from the anal margin to the tumor has the strongest effect on major LARS occurrences. This result was similar in the nomogram reported by Battersby NJ, et al.. These results suggested that LARS severity might depend on the volume of the remaining rectum.
We found that age also strongly affected the development of major LARS in our nomogram. Older individuals have a weak anal sphincter muscle, which prevents control of gas or stool passage. Therefore, fecal incontinence after rectal cancer surgery might be expected to occur more frequently in older patients. However, interestingly, we found that younger patients tended to have higher LARS scores in this study, consistent with findings in the previous European study. When compared by age, there was no apparent difference in clinical characteristics, as shown in Supplemental table 1. On the other hand, comparing the results of the LARS survey, younger patients had higher scores than older patients in the question about the sense of urgency in defecation (Q5), although they showed little or no differences in the scores for questions 1-3, as shown in Supplemental table 2. This result suggested that younger patients felt more fecal urgency than older patients, despite the fact that rectal cancer surgery can cause stool and fecal incontinence, regardless of age.
Gender was also a correlating factor as well as the other report. In the present study, men were more likely to develop major LARS. However, men generally have a narrower pelvic floor than women, which makes it more difficult to manipulate and puts more external stress on the surrounding tissues, including the pelvic floor muscles, which may have led to defecation problems. On the other hand, the European nomogram suggests that women are more likely to develop major LARS and to have defecation disorders due to damage to the pelvic floor muscles caused by childbirth. Thus, the nomogram has a problem that the results may differ depending on the background of the subject, and the application of the nomogram needs to be carefully examined. In fact, the AUC of the European nomogram was 0.60 in the present study of 160 patients, and our nomogram showed higher accuracy.
The present study had some potential limitations. First, it was a single center study, and 47 patients developed major LARS in the learning set. This number might have been insufficient to create a predictive model for major LARS. Furthermore, the number of verifications of our predictive model was also an insufficient number of cases. In the future, we would like to verify our predictive model and conduct a multicenter prospective study.