[R1 resection in rectal cancer]

R1 resections in rectal cancer particularly affect the circumferential resection margin (CRM) and lead to increased local recurrence rates, more distant metastases and a poorer prognosis. The proximity of the tumor to the CRM is already sufficient to increases these risks; therefore, according to the guidelines, it is now necessary to distinguish between R0 wide (≥1 mm distance), R0 close (<1 mm) and R1. The surgical technique is decisive for avoiding R1 situations. The preparation follows the boundary layers and envelope fascia in a standardized radical way and if necessary deviates away from these structures and the tumor under en bloc resection of neighboring structures. Neoadjuvant therapy also contributes to the reduction of R1 situations but cannot compensate for inadequate surgical procedures.