sphincter-preserving low anterior resection (LAR) improves the quality of life (QoL) of patients with middle and low colorectal cancer; Therefore, it has become a popular treatment method[27, 28]. However, the undesirable result of this procedure is the bowel dysfunction called low anterior resection syndrome. About 80% of patients who undergo this procedure experience varying degrees of LARS[30, 31].
There are two types of LARS. The first includes fecal urgency, incontinence, and increased frequency. The second includes constipation, feelings of incomplete excretion, and bowel-emptying difficulties[10, 20]. Some patients show characteristics of both types. They alternate between the two patterns or experience both at the same time[32–35]. these symptoms are caused because of damage to several factors, such as nerves and muscles of defecation[22, 28, 36].
The risk factors of severe LARS are related to the anastomotic height, pre and postoperative chemoradiotherapy, anastomotic leakage, and protective ileostomy etc.[8, 9, 34, 37, 38].
In our study, we firstly identified the independent risk factors associated with LARS in univariate analysis, including tumor location and tumor size, anastomotic height, protective ileostomy versus no ileostomy, post-operation chemoradiotherapy, tumor T stage, nodal classification, long surgery duration, and time interval between ileostomy closure, while the tumor T stage and nodal classification were clarified as the new independent risk factors compared with the last decade studies.
When having low anterior resection procedure for CRCs, it takes time for the bowel to adapt after the operation, which helps in intestinal function recovery. And protective ileostomy was performed, the patients have difficulties controlling their defecation. The loss of bowel functions leads to stool defecation without consciousness, and this phenomenon adversely affects LARS recovery.
tumor location, size, T stage and lymphatic nodal characteristics are directly related to surgical range and procedures; therefore, LARS is directly influenced by these three factors[39–41]. But this theory is suggested in our study and the other studies have no mentioned the tumor T stage and nodal classification as the risk factors in their researches.
the side effect of neoadjuvant radiotherapy and chemotherapy is intestinal dysfunction, which is caused by nerve and muscle damage in the colon[38, 42–44]. In 2017, L.M.Jimenez-Gomez et al., reported risk factors, such as TME and neoadjuvant and adjuvant radiotherapy can increase the risk of major LARS. In 2020, Theresa H. Nguyen et al., proved that neoadjuvant and adjuvant radiotherapy were risk factors for LARS, especially major LARS, even in patients with large rectal residuals. And several studies have shown that LARS is divided into incontinence-dominant and frequency-dominant modes. Each mode is associated with different risk factors. The incontinence-dominant mode is related to preoperative radiotherapy and postoperative complications. the frequency-dominant mode is related to the low tumor location from the anal margin; however, the overall main LARS is related to poor quality of life. The frequency-dominant type of LARS has a more profound impact on postoperative quality of life[10, 26, 45]. In 2019, Keiji Koda et al., showed that removing most of the rectum can damage the internal sphincter muscle and/or rectal wall, and deconstruct structures around the levator hiatus, are factors involved in the development of LARS symptoms.
In recent years, significant incidences of postoperative intestinal dysfunction and the prospects of a good prognosis have made radical resection plus neoadjuvant radiotherapy the standard treatment. However, there are some practical difficulties to perform the complete radical resection. In this theory, full-dose neoadjuvant chemotherapy can reduce tumor size similar to radiotherapy plus chemotherapy, reducing the possibilities of local recurrence in patients undergoing surgical resection. It also reduces the incidences of distant metastases. These studies have shown that neoadjuvant chemotherapy is usually an effective method for the treatment of locally advanced rectal cancer, and the effects are satisfactory[46, 47]. Considering that neoadjuvant chemotherapy has no significant effect on bowel function, it may be a reasonable treatment option for major LARS patients.
In our study, only post-operative chemoradiotherapy was identified as a risk factor for severe LARS development in terms of neoadjuvant and adjuvant treatment of CRCs. We thought that this result came from the differences in treatments and conditions according to every country and national race.
In 2021, Suzuki, N et al., also reported anastomotic complications, such as leakage, which was confirmed to be associated with a 3.5-fold increase in the incidences of major LARS. However, we could not find anastomotic complications increasing the incidences of major LARS in our study, and we thought this was due to the development of operation skills and reliable management of patients after operation in recent years.
several studies have suggested an algorithm for the treatment of LARS, including conservative therapies, biofeedback, and sacral nerve stimulation. In 2019, Chirs George et al., reported that conservative treatment (internal medicine, physical therapy, and trans-anal irrigation), invasive surgery (neuromodulation), and multimodal therapy were the main methods for treating LARS in patients. If these treatments were not working wonderfully, it’s recommended to perform stoma surgery. the definitive stoma surgery was considered if major LARS persisted for more than 2 years [7, 21, 28]. In 2021, K. Neumann et.al., found that transanal endoscopic microsurgery (TEM) for rectal tumors was associated with significantly reduced hospitalization costs, which far exceeded the cost of acquiring and maintaining the technology, and reduced the incidence of LARS, so recommended that if possible use TEM to treat rectal cancer.
When we are focusing on the number of articles published each year for the last ten years, the publications and citations trend to increase obviously (Fig. 2: downloaded from Web of Science Core Collection). this shows that research for LARS and improving QoL is recently one of the major focuses in the colorectal fields as patient requests. And, the independent factors are similar to the others, including pre- and post-surgery chemoradiotherapy, poor TME procedure, tumor height from the anal verge, anastomosis height and leakage, temporary protective ileostomy, and complications after surgery (Table 5). we thought it would give a well-updated knowledge for future studies. We thought there are some limitations in our study such as not enough numbers of database, single institution study design and no mentions on LARS treatment. these can affect the undesirable effects on the study results and general ideas. We hope an updated and advanced study is needed for a better understanding to provide more information on LARS treatment strategies improving the quality of life.