The primary purpose of this study is to compare the differences of oncological in rectal cancer patients undergoing laparoscopic or transanal endoscopy radical resection. The secondary purpose is to compare the effect of two different surgical methods on prognosis.

Transanal total mesorectal excision (taTME) is a new surgical procedure for total mesorectal excision (TME) by dissociating the mesorectum from the bottom through transanal endoscopic. The characteristics of TaTME are mainly summarized as transanal reverse operation, no auxiliary abdominal incision, complete mesorectal excision and specimen removal through the anus. So taTME is a natural orifice specimen extraction procedure (NOSES). However, similar to NOSES, the specific surgical approach to taTME surgery may raise oncological safety concerns. Due to the premature contact with the tumor, the squeezing of the tumor cannot be avoided during the operation. The tumor may also be squeezed when the specimen is removed through the anus, putting the tumor cells at risk of shedding into the abdominal and pelvic cavity.

Whether TaTME is safe and feasible still needs strong evidence-based medical evidence. However, there have been prospective studies related to oncological in NOSES surgery, but there is a lack of prospective clinical studies on the issue of oncological diffusion during taTME surgery. Therefore, the investigators conducted a randomized controlled study to collect the abdominal and pelvic irrigation fluids in the transanal and laparoscopic TME surgery for oncological examination, to clarify the influence of the two different surgical methods on the intraoperative oncological diffusion. The purpose of this study was to clarify the effect of two different surgical methods on intraoperative tumor cell proliferation, and to compare the long-term oncological outcomes of the two surgical methods, so as to provide more evidence-based medical evidence for the safety of taTME surgery.

Inclusion Criteria:

• Primary rectal carcinoma
• Single lesion
• No metastasis

Exclusion Criteria:

• History of malignant tumors
• Acute bowel obstruction, bleeding or perforation
• Tumor over 6cm in diameter or in severe adhesion with surrounded tissues
• Severe other contradictions of surgery
• Pregnant women will be excluded

192 rectal cancer patients will be enrolled. Patients must be older than 18 years.