Local recurrence rates in rectal cancer have reduced dramatically since the introduction of the total mesorectal excision (TME) technique. These rates have been lowered further with the use of neoadjuvant (chemo)radiotherapy ((C)RT) regimens in appropriate cases, decreasing overall rates of 5-year local recurrence to 5-10%. However, in patients with enlarged lateral lymph nodes (LLNs, ≥7mm short-axis size), recurrence rates have remained high, up to 20%. Most likely, this is caused by lymphatic spread of low rectal cancer to the lateral compartments. Western surgeons have always relied on (C)RT to sterilize the lateral compartments, containing the internal iliac and obturator lymph nodes, alleviating fears of operative morbidity and nerve function disorders associated with a lateral lymph node dissection (LLND), mainly performed in the East. Furthermore, most Western clinicians consider lateral nodal disease to represent metastatic disease, not amendable to cure.

The Lateral Node Consortium undertook a multi-centre study with 12 centres from seven countries, collecting data over a 5-year period, including all consecutive patients operated for a cT3 or T4 rectal cancer. In all patients, every series of MRIs was re-reviewed by a standardized protocol, examining lateral pelvic nodes, defining these according to size and the presence of malignant features and relating these to the development of locally recurrent disease. In the first publication of the consortium with a total of 1216 patients, it was shown that pre-treatment lateral lymph node (LLN) size of ≥7 mm, results in an unacceptably high incidence of lateral local recurrence of 20%, despite (C)RT with TME. Within the consortium, several centres performed LLND's after (C)RT, which resulted in a significantly lower rate of lateral local recurrence of 6% in nodes ≥7 mm (p = 0.042). Furthermore, LLN enlargement did not influence distant metastases rate, suggesting it is a local issue which requires to be addressed through targeted treatment in the pelvis, rather simply representing a marker of poor prognosis and distant disease.

Additionally, a second study, the Snapshot Rectal Cancer 2016 was conducted in 2020. This national retrospective cohort study included 3057 patients operated for rectal cancer in 2016 with a 4-year follow-up period. Radiologists were trained for LLN classification and measurements and re-reviewed MRIs of 882 patients with low (≤8cm from the anorectal junction), cT3/4 rectal cancer who received neoadjuvant (chemo)radiotherapy with the help of two atlases. This study found a 4-year LLR risk of 15% in presence of enlarged LLNs.

The major drawback of these multi-center studies are their retrospective nature. Radiological reporting of LLNs was low for primary MRIs, which may have influenced treatment decisions. Consequently, LLNs may have not been separately included in irradiation field. Moreover, neither study was able to investigate the effect of LLND in a trained setting. In the Netherlands, radiologists, radiation oncologists, surgeons and pathologists have recently been educated and trained to enhance knowledge and awareness of LLNs and to implement nerve-sparing minimally invasive LLND. The LaNoReC describes a prospective evaluation of oncological outcomes after multi-disciplinary training, thereby aiming for a 50% reduction in LLR rates.