摘要目的:探讨直肠肿瘤环周位置（直肠前壁、非前壁或环周）对中低位直肠癌患者环周切缘状态、局部复发及生存的影响。方法:本研究采用回顾性队列研究方法。分析2018年12月至2019年12月期间，海军军医大学第一附属医院肛肠外科收治的696例中低位直肠腺癌手术患者的病历资料。基于MRI或增强CT检查所见肿瘤位置，将直肠壁分为前、后、左、右4个分区，有245例患者肿瘤主体位于前壁，即为前壁组；286例肿瘤主体位于后壁或侧壁，为非前壁组；165例肿瘤侵犯范围≥3/4肠周，为环周组。采用倾向性评分匹配（PSM）平衡组间的基线资料差异，比较3组患者手术的病理环周切缘阳性率及术后局部复发率（LRR）、总生存期（OS）和无病生存期（DFS）。采用Cox回归分析肿瘤复发的危险因素。对未行新辅助治疗的患者进行分期亚组分析。结果:PSM后，前壁组和环周组病理环周切缘阳性率显著高于非前壁组（分别为 P=0.040和 P=0.039）。全组中位随访时间64（1~71）个月。前壁组与非前壁组比较，前壁组5年LRR显著升高（8.8%比2.3%， P=0.003），5年OS（80.7%比91.6%， P=0.001）和DFS（76.6%比84.6%， P=0.029）明显降低；环周组与非前壁组比较，5年LRR（11.4%比3.8%， P=0.020）显著更高，但5年OS（81.8%比89.5%， P=0.100）和DFS（70.7%比78.3%， P=0.101）差异无统计学意义。前壁组与环周组比较，5年LRR（11.1%比9.7%）、OS（76.3%比83.7%）和DFS（69.8%和74.1%）差异均无统计学意义（均 P>0.05）。Cox单因素和多因素分析显示，前壁肿瘤（HR=3.751，95%CI：1.373~10.215， P=0.010）、环周肿瘤（HR=3.240，95%CI：1.109~9.466， P=0.032）和病理环周切缘阳性（HR=3.071，95%CI：1.144~8.245， P=0.026）以及有淋巴结转移（HR=2.584，95%CI：1.192~5.601， P=0.016）是本组患者发生局部复发的独立危险因素，而肿瘤距肛缘距离越远（每增加1 cm，HR=0.831，95%CI：0.712~0.970， P=0.019）和接受新辅助治疗（HR=0.442，95%CI：0.204~0.957， P=0.038）则是本组患者发生局部复发的独立保护因素。未接受新辅助治疗的局部进展期非前壁肿瘤呈现超低本组患者局部复发（pⅡ~Ⅲ期1.3%，pT3~4期1.6%）。 结论:位于前壁及环周的直肠肿瘤CRM阳性率和局部复发风险更高、生存更差，应优先进行新辅助治疗。非前壁肿瘤复发率低，可考虑选择性豁免新辅助治疗。

abstractsObjective:To investigate the impact of circumferential tumor location (anterior wall, nonanterior wall, or circumferential) on circumferential resection margin (CRM) status, local recurrence, and survival in patients with mid-low rectal cancer.Methods:A retrospective cohort study was conducted using data from 696 patients with mid-low rectal adenocarcinoma who underwent surgery in the Department of Colorectal Surgery at the First Affiliated Hospital of Naval Medical University between December, 2018 and December, 2019. Based on MRI or contrast-enhanced CT findings, the rectal wall was divided into four quadrants: anterior, posterior, left, and right. Tumors were classified into three groups: anterior wall group ( n = 245), nonanterior wall group ( n = 286, tumors predominantly located on the posterior or lateral walls), and circumferential group ( n = 165, tumors involving ≥ 3/4 of the circumference). Propensity score matching (PSM) was used to balance baseline characteristics. Outcomes included pathological CRM positivity, local recurrence rate (LRR), overall survival (OS), and disease-free survival (DFS). Cox regression analysis was performed to identify risk factors for recurrence, and subgroup analysis was conducted in patients who did not receive neoadjuvant therapy. Results:After PSM, both the anterior and circumferential groups had significantly higher pathological CRM positivity rates compared to the nonanterior wall group ( P=0.040 and P=0.039, respectively). The median follow-up time was 64 months (range: 1-71 months). Compared to the nonanterior wall group, the anterior wall group also had a significantly higher 5-year LRR (8.8% vs. 2.3%, P=0.003), and significantly lower 5-year OS (80.7% vs. 91.6%, P=0.001) and DFS (76.6% vs. 84.6%, P=0.029). The circumferential group had a significantly higher 5-year LRR than the nonanterior wall group (11.4% vs. 3.8%, P=0.020), but no significant differences were observed in 5-year OS (81.8% vs. 89.5%, P=0.100) or DFS (70.7% vs. 78.3%, P=0.101). No significant differences were found between the anterior and circumferential groups in 5-year LRR (11.1% vs. 9.7%), OS (76.3% vs. 83.7%), or DFS (69.8% vs. 74.1%) either (all P>0.05). Cox univariate analysis and multivariate analysis identified anterior wall tumors (HR=3.751, 95%CI: 1.373-10.215, P=0.010), circumferential tumors (HR=3.240, 95%CI: 1.109-9.466, P=0.032), pathological CRM positivity (HR=3.071, 95%CI: 1.144-8.245, P=0.026), and lymph node metastasis (HR=2.584, 95%CI: 1.192-5.601, P=0.016) as independent risk factors for LRR. Conversely, a greater distance from tumor to the anal verge (per 1 cm increase, HR=0.831, 95%CI: 0.712-0.970, P=0.019), and neoadjuvant therapy (HR=0.442, 95%CI: 0.204-0.957, P=0.038) were identified as independent protective factors against LRR. In patients who did not receive neoadjuvant therapy, locally advanced nonanterior wall tumors exhibited markedly low LRR (1.3% for pathological stage II-III, 1.6% for pT3-4 stage). Conclusion:Rectal tumors located in the anterior wall or involving the circumference are associated with higher CRM positivity rates, increased local recurrence, and poorer survival. These patients should be prioritized for neoadjuvant therapy. In contrast, nonanterior wall tumors have a low recurrence rate, and selective omission of neoadjuvant therapy may be considered for these cases.