Have a look at the ESMO guidelines.
Early rectal cancer not suitable for local excision [cT1–cT2; cT3a/ b if middle or high, N0 (or also cN1 if high), MRF clear, no EMVI].
More advanced tumours up to and including cT2c/T3a/b should be treated by radical TME surgery because of higher risks of recurrence and the higher risk of mesorectal lymph node involvement.
...
These early, favourable cases, which are not suitable for local excision, i.e. cT1-2 but with adverse pathological features (e.g. G3, V1, L1), and some cT3a/b without clear involvement of MRF (MRF-) according to MRI, when located above the levators, may be appropriate for surgery alone with TME [II, A], as the risk of local failure is very low. Although not prospectively assessed, EMVI on MRI, even in the case of cT3a/b tumours, confers a higher risk of local and distant recurrence.
Intermediate/more locally advanced rectal cancers [cT3a/b (very low, levators clear, MRF clear or (cT3a/b in mid- or high rectum, cN1-2 (not extranodal), no EMVI].
The routine delivery of preoperative RT, either CRT or short-course preoperative radiotherapy (SCPRT), to all patients with imaging predicted cN+ remains controversial in view of the poor accuracy if categorised by nodal size alone, and the lack of prognostic relevance of the preoperative MRI assessment of involved lymph nodes on the risk of local recurrence. This is particularly valid because data suggest a low risk of local recurrence if the surgeon routinely carries out good-quality TME and removes the mesorectal nodes en bloc. However, it is the responsibility of the surgeon to demonstrate that consistent, good-quality TME is being achieved.
Locally advanced rectal cancers (>cT3b, and EMVIþ).
For patients with LARC, treatment decisions regarding neoadjuvant therapy should be based on preoperative, MRI-predicted CRM
( 1 mm), EMVI and more advanced T3 substages (T3c/T3d), which define the risk of both local recurrence and/or synchronous and subsequent metastatic disease. MRI also allows risk stratification in terms of the predicted required extent of surgery, and the achievement of a clear CRM (>1 mm). For resectable cancers, where there is no indication on MRI that surgery is likely to be associated with either an R2 or an R1
resection, standard TME should achieve a curative resection, and downstaging/downsizing is not necessary to achieve this. The use of CRT or SCPRT aims to reduce local recurrence.
...
Previous recommendations aimed to reduce the overall risk of an involved CRM to < 3% and local recurrence to (preferably) < 5% in the population in whom curative treatment is intend. Evidence from the UK CR07 trial suggests that, without RT, a local recurrence rate of 5% (27/543) can be achieved if a complete mesorectal excision is carried out with a negative CRM. MDTs and surgeons are, therefore, required to audit their local recurrence rates. There are recognised long-term adverse consequences of surgery and RT. Symptoms such as chronic pain, faecal incontinence and sexual difficulties are reported in both sexes. Good communication between surgeons, clinicians and patients will optimise joint decision-making.
Tumours with threatened resection margin.
The terms ‘unresectable/borderline cancers’ (i.e. cT4, with the resection margin at risk, involved MRF or CRMþ) are imprecise, but MRI can predict rectal cancers that are unlikely to be amenable to a curative resection without multivisceral resection, either because the tumour abuts or breaches the MRF or there is macroscopic tumour outside the MRF with local extension to pelvic side wall and sacrum or in terms of tumour spread involvement into the lateral compartment. In these circumstances, preoperative treatment is necessary to shrink the cancer back away from the threatened margin i.e. the MRF/CRM. Without preoperative treatment or in the case of no response, surgery is likely to lead to either an
R1 or an R2 resection. For such patients, CRT has been shown to significantly increase the chance of performing an R0 resection compared with RT alone.
You see what the picture is over here?
We are left with "tumours with threatened resection margin" more or less...
Kinda crazy that radiotherapy got omitted without any phase III data to back up that decision
