Role for Lateral Node Dissection in Low Rectal Cancer

Use of lateral lymph node dissection -- a technique not commonly employed in the U.S. -- can be avoided in certain patients with low rectal cancer, but should be "seriously considered" for those with persistently enlarged lymph nodes in the iliac compartment after neoadjuvant treatment, said researchers from the Lateral Node Study Consortium.

At 3 years post-surgery, no cases of lateral node recurrence were detected among 28 patients whose nodes shrunk from a short-axis size of 7 mm on primary magnetic resonance imaging (MRI) to below 4 mm on restaging MRI, reported Atsushi Ogura, MD, from Leiden University Medical Center in the Netherlands, and colleagues.

Writing in JAMA Surgery, they said that this level of shrinkage -- which occurred in 29% of patients -- "abolishes" this local recurrence risk and defines "an important group in whom lateral lymph node dissection can be avoided, as it probably offers no benefit."

However, patients with lateral nodes in the internal iliac compartment that were 7 mm or greater on primary MRI and remained larger than 4 mm when restaged had a 5-year lateral local recurrence risk of 52.3% with neoadjuvant chemoradiotherapy/radiotherapy plus total mesorectal excision compared with 8.7% in those also treated with lateral lymph node dissection (HR 6.2, 95% CI 1.4-28.5, P=0.007).

In addition to size, the finding that lateral node location is a factor in outcomes has not previously been reported, Ogura's team wrote. Persistently enlarged nodes in the internal iliac compartment carried almost six times the risk for 5-year lateral local recurrence compared with nodes in the obturator compartment (52.3% vs 9.5%; HR 5.8, 95% CI 1.6-21.3, P=0.003).

"It is known from Japanese studies that malignant lateral lymph nodes were most frequently located in the internal iliac compartment after lateral lymph node dissection, the rationale behind this being that they are the first basin directly from the lateral ligament," the authors explained.

But why the 5-year lateral local recurrence rate is far lower for nodes in the obturator compartment that are similarly large and unresponsive "remains a mystery," they said.

Important Step

In an editorial that accompanied the study, Linda Ferrari, MD, of St. Thomas' Hospital in London, and Alessandro Fichera, MD, of the University of North Carolina at Chapel Hill, wrote that this study is an "important first step" toward identifying patients at high risk of local recurrence who could potentially benefit from more aggressive surgery.

"Defining the size and location of the lymph nodes at high risk of recurrence will help surgeons select patients who may benefit from lateral lymph node dissection," they wrote. "This would be another step toward a tailored surgical approach to patients with locally advanced rectal cancer, based on solid scientific evidence."

According to Ferrari and Fichera, neoadjuvant treatment followed by total mesorectal excision has been the standard of care in Western countries for 2 decades, in contrast to Eastern countries where prophylactic lateral lymph node dissection is the standard.

However, they noted that the Lateral Node Study Consortium included institutions from Eastern and Western countries, meaning that it had heterogeneity in surgical techniques, indications for lateral lymph node dissection, length of radiotherapy, and descriptions of radiation fields. Therefore, "more definitive standardization of surgical and radiotherapy techniques is needed to reach definitive conclusions."

Study Details

The retrospective, pooled cohort study included data from 741 patients from 12 centers in seven countries who underwent surgery for cT3 or cT4 low rectal cancer from 2009 to 2013. Included patients had primary MRI, underwent chemoradiotherapy or radiotherapy, and had a restaging MRI. Patients were treated with either total mesorectal excision alone (n=651) or with lateral lymph node dissection (n=90).

In the group that did not receive lateral lymph node dissection, a short-axis lateral node of 7 mm or greater on primary MRI resulted in a 5-year lateral local recurrence rate of 17.9%, which was significantly higher than the 4.1% rate for those with a node size smaller than 7 mm (P<0.001).

For nodes in the obturator compartment, there was no difference between lateral local recurrence in patients with a short-axis node size of 7 mm or greater on primary MRI that remained larger than 4 mm on restaging MRI with or without use of lateral lymph node dissection.