In the middle of the 1980s, it was shown that involvement of the lateral or circumferential resection margin (CRM) was the most important factor for the risk of local recurrence after rectal cancer surgery,¹ and considerably more relevant than the distal or proximal resection margins. The relevance of a positive CRM (CRM+), not only for local but also systemic failure, has been confirmed in many subsequent studies.²

According to multiple randomized clinical trials,^3–5 both preoperative and postoperative radiotherapy/chemoradiotherapy diminish the risk of local recurrence. Therefore, these treatments are standard of care for many patients with primary rectal cancer who are at risk for local recurrence. The relative risk reduction seems to be larger when the absolute risk of local failure is low, compared with when it is higher.^6,7 The treatments can therefore not compensate for inappropriate or nonradical surgery, that is, CRM+. Because several studies have shown that preoperative radiotherapy/chemoradiotherapy is more efficient and less toxic than postoperative therapy,^7–10 it has become increasingly important to evaluate the risk of CRM+ before the operation. Magnetic resonance imaging is the imaging modality that can most accurately evaluate this risk.^11–14 The decision to undertake additional preoperative therapy is generally made at multidisciplinary team (MDT) conferences on the basis of clinical information and the proximity to or involvement of the mesorectal fascia (MRF) that surrounds the mesorectal fat outside the rectum, or the sphincters in the lowest part. There is presently little consensus on staging.¹⁵ Of the preoperative features, the potential CRM or the relationship of the tumor to the MRF has emerged as one of the most powerful predictors of outcome. Surgical dissection outside of this fascia has become central in the efforts to achieve CRM negativity and is possible in many cases. This is the concept behind the total mesorectal excision (TME) approach.¹⁶ The discussions at MDT conferences basically focus on four issues: whether surgery alone is an appropriate therapy; whether preoperative therapy is needed to achieve sufficiently low local recurrence rates; whether there is a need for an interval between the preoperative therapy and surgery; and whether more extensive surgery is needed after preoperative radiotherapy/chemoradiotherapy.¹⁷ In the first situation, the tumor presentation is often considered as favorable (or good), in the second as intermediate (bad), and in the third and fourth as unfavorable or locally advanced (ugly).^17–19 The extent of the extramural growth, the presence of radiologically pathologic lymph nodes and/or extramural vascular invasion, the relationship to the pelvic floor and anal canal, but above all, the proximity of the tumor or pathologic lymph nodes to the MRF or actual infiltration into the MRF are central in this evaluation.

The term CRM+ has repeatedly been used in trial protocols, consensus documents, and scientific articles to refer to proximity to the MRF, irrespective of whether that distance is < 1 mm or < 2 mm. The term indicates that there is a risk that CRM will be involved after surgery, in the TME plane, but this term is inappropriate preoperatively because whether the CRM is involved is decided by the surgical plane.^20,21 Several, if not all, authors of this commentary have used the expression CRM to refer to closeness to or involvement of the MRF or another anatomic structure, although this is incorrect. We propose that, preoperatively, the term CRM should no longer be used. Postoperatively, CRM is the appropriate term.

Preoperatively, the extent of the tumor, including pathologic lymph nodes, should be described in relation to an adjacent anatomic structure. In this respect, the MRF is central, but other anatomic structures can also be relevant. If the MRF is involved or if the tumor extends to a point that is within 1 mm from the MRF, there is a clear risk that CRM will be involved if only a TME is performed. In particularly low rectal tumors, the anal sphincters constitute the corresponding significant border because the MRF does not extend past the puborectal muscle. The surgery should then either be more extensive than a TME, for example, performed in the extralevator plane rather than in the levator plane when an abdominoperineal resection is required,^20,23,23 or additional antitumor treatment that has the capacity to kill all tumor cells at the edge of the tumor should be administered preoperatively.

The reason for suggesting a change in terminology, although the terminology presently being used has been used for years in many trial protocols, consensus documents, and so on, is primarily that the term CRM is conceptually incorrect when it is used in the preoperative setting of risk assessment, whether that assessment is performed by imaging or other means. The use of CRM in this situation has been detrimental to discussions at MDT conferences and at scientific meetings that are focused on making the best decision for an individual patient or for groups of patients. This has become particularly apparent with respect to low rectal cancers that are growing close to or into the levator muscles or the sphincters. In these cases, there has been a clear trend toward the use of chemoradiotherapy (in fact, it is thought to be always required), although the appropriate measure would rather be to perform more suitable surgery.^20,22,24,25 More extensive surgery will decrease the risk of CRM+, and thus the risk of a local failure, but will not automatically improve survival because the risk of systemic relapse is likely more associated with the tumor extent than CRM+ per se.

To conclude, we advocate the use of the terminology MRF instead of CRM in the preoperative staging of patients with rectal cancer. In particularly low tumors that are below the levator muscles, where the MRF cannot be defined, the relationship to the sphincters should be described.