RESUMEN
Rectal cancers are currently defined as tumours below 15 cm from the anal verge on rigid sigmoidoscopy. Clinical trials have used this criterion to select patients for neoadjuvant chemoradiotherapy, but several authors have shown that the distance between the fully peritonealized sigmoid colon and the anal canal varies significantly between individuals. A fixed anatomical landmark would be a more reliable and reproducible method of demarcating the junction between the colon and the rectum. The distinction between rectal and sigmoid colon cancers is of particular importance as treatment protocols for rectal cancer management often involve neoadjuvant treatment in contrast to colonic cancers, so it is vital to get the anatomy right. As all rectal cancers are now assessed preoperatively by MRI, the use of a bony landmark is possible. We postulate that the fixed landmark to define the upper limit of the rectum should be the sacral promontory.