A Prospective, Multicenter Randomized Controlled Study of the Application of Preoperative FOLFOXIRI Chemotherapy Combined With Lateral Lymph Node Dissection in Low- and Medium-lying Rectal Cancer With Lateral Lymph Node Metastasis

Inclusion Criteria: * Age 18-70 years old, gender is not limited; * The clinical stage based on magnetic resonance imaging (MRI) is cT1-4aN+M0 (according to AJCC Cancer Staging Manual, 8th Edition, 2018). * Meet the criteria for lateral lymph node metastasis (lymph node short diameter ≥7mm, or lymph node short diameter ≥5cm with uneven internal signals and no chemical shift effect, or irregular boundaries); * The primary tumor was located in the rectum (hard tube proctoscopy indicated that the lower margin of the lesion was less than 10cm from the anus); * Kastler score ≥70, ECOG score 0 or 1; * Meet the following laboratory diagnostic indicators: hemoglobin ≥100g/L, white blood cells ≥3.5×109 /L, neutrophil ≥1.5×109/L, platelet ≥100×109/L; Creatinine ≤1.5× upper limit of normal (UNL); Urea nitrogen (BUN) ≤1.5 upper limit of normal (UNL) alanine aminotransferase (ALT), aspartate aminotransferase (AST) ≤2.5×UNL, alkaline phosphatase (ALP) ≤2.5×UNL, total bilirubin (Tbil) ≤2.5×UNL; Urinary protein (-); Clotting time is normal. * Patients with primary locally advanced rectal cancer required that they had not received surgery, radiotherapy, chemotherapy or other antitumor therapy from diagnosis to enrollment; No previous pelvic radiation; * Subjects voluntarily join the study and sign the informed consent. Exclusion Criteria: * A history of malignancy at other sites, excluding curable non-melanic skin cancer and carcinoma in situ of the cervix; * Unable to complete MRI; * P…