Elaboration of a preoperative prediction model of the quality of the mesorectum and the involvement of the circumferential margin in patients with mid-low rectal cancer who undergo laparoscopic anterior rectal resection.

In a second phase the investigators will study the utility of the prediction model in classifying patients with high risk of suboptimal quality of mesorectum and/or positive circumferential margin. Patients with high preoperative risk will undergo a transanal total mesorectal excision and patients with low risk a laparoscopic transabdominal mesorectal excision. The investigators finally will compare pathological outcomes ( quality of mesorectum and circumferential margin), survival and recurrence between the two groups.

Inclusion Criteria:

• Patients directed to laparoscopic anterior rectal resection through a transabdominal or a transanal approach.
• Age ≥ 18 years
• Histology of adenocarcinoma or adenoma
• With or without neoadjuvant chemoradiotherapy
• TNM classification: T2 or T3, any N stage or M stage
• Intention of resection R0

Exclusion Criteria:

• TNM classification: T1 or T4.
• Complicated rectal cancer or emergency surgery.
• Previous major colorectal surgery

Patients affected of mid-low rectal cancer