Rectal cancer is one of the most common malignant tumors, with 9% to 23% of patients experiencing pelvic sidewall lymph node metastasis. According to the current Chinese guidelines for diagnosing and treating colorectal cancer, pelvic sidewall lymph node dissection is recommended for patients who have experienced or are suspected of having lateral lymph node metastasis. Lateral lymph node dissection can result in longer operation times, increased bleeding, and complications such as urinary and sexual dysfunction after surgery. Currently, the presence of metastasis is primarily determined by the size and enhancement characteristics of lateral lymph nodes observed through imaging studies. However, the pathological lymph node metastasis rate of specimens collected after lateral lymph node dissection based on current imaging criteria is only 20.5%. Therefore, a pressing clinical challenge is accurately determining the presence of lateral lymph node metastasis and avoiding unnecessary lateral lymph node dissection in patients who have not experienced lateral lymph node metastasis.

Sentinel lymph node biopsy has been widely used in clinical practice. It has replaced traditional lymph node dissection in some breast cancer and melanoma patients, reducing surgical risks and complications and improving patients' quality of life. This study aims to use indocyanine green as a tracer for fluorescence-guided laparoscopic navigation to locate the lateral sentinel lymph nodes of rectal cancer in the pelvic cavity. By studying the accuracy, specificity, and false-negative rate of predicting lateral lymph node status using the sentinel lymph node, we can further clarify the clinical significance of the lateral sentinel lymph node.

This study is a prospective single-arm clinical study. 87 patients with middle and low rectal cancer are planned to be included in the study. After general anesthesia during the operation, indocyanine green is injected around the tumor through the anus. After the sentinel lymph nodes are developed and located by fluorescent laparoscopy, they are removed and sent to rapid frozen pathological examination, and then the lateral lymph nodes are cleaned. Through pathological examination and statistical analysis of the fluorescent stained lateral sentinel lymph nodes and all the cleaned lateral lymph nodes, To evaluate the clinical significance of lateral sentinel lymph nodes located by this technique in predicting the status of lateral lymph nodes.

Inclusion Criteria:

• Aged 18 to 75 years old.
• Eastern Cooperative Oncology Group (ECOG) performance status (PS) score of 0-1.
• Newly diagnosed patients with confirmed rectal cancer by histopathology.
• Preoperative clinical staging by imaging examination is T3-4.
• Preoperative colonoscopy shows the distance from the tumor's lower edge to the anus is less than 10cm.
• No previous chemotherapy or radiotherapy.
• Preoperative imaging examination (pelvic enhanced MRI) shows lateral lymph nodes with a maximum short diameter of ≥5mm and <10mm.
• Women of childbearing age must take effective contraceptive measures.
• Able to understand the study and sign the informed consent form.

Exclusion Criteria:

• Complete intestinal obstruction.
• Active hepatitis and peripheral neuropathy (such as peripheral neuritis, pseudomeningitis, motor neuritis, sensory disturbances, etc.).
• Pregnant or lactating women; women of childbearing potential who have not taken sufficient contraceptive measures.
• History of other tumors or previous chemotherapy or radiotherapy.
• Alcoholism or drug addiction.
• Significant organ dysfunction or other significant diseases, including clinically relevant coronary artery disease, cardiovascular disease, or myocardial infarction within 12 months before enrollment; severe neurological or psychiatric history; severe infection; active disseminated intravascular coagulation.
• Hypoproteinemia.
• Preprandial blood glucose control exceeds 11.2mmol/L in the week before surgery.
• BMI>28 kg/m^2.
• Poor compliance, and failure to comply with the study protocol.
• Subject withdrawal from the study

Participants' data are only allowed to be used for the analysis of this study and are not authorized to be shared with other researchers.