Sentinel lymph node mapping accurately predicts nodal status in >90 percent of melanoma and breast and colorectal cancers.
However, because of anatomic differences, sentinel lymph node mapping of rectal cancers has been considered inaccurate and difficult relative to colon.
Dr Sahal and colleagues from Michigan, America undertook a prospective study in order to identify differences in sentinel lymph node mapping between patients with colon cancer and those with rectal cancer.
At operation, clinicians injected 1 to 3 ml of 1% isosulfan blue dye subserosally around colon cancers.
The investigators were able to see the first to fourth blue-staining nodes within 10 minutes of injection and these were marked as sentinel lymph nodes.
For cancer of the mid-rectum to low rectum, the clinicians injected dye submucosally via rigid scope and spinal needle.
The researchers dissected the mesorectum ex vivo to identify blue nodes nearest the tumor as sentinel lymph nodes.
|Sentinel lymph nodes were identified in 99.1% of colon and 91.5% of rectal patients|
|Diseases of the Colon and Rectum|
The investigators then stained multilevel microsections of sentinel lymph nodes with hematoxylin and eosin and also immunostained sections for cytokeratin.
The researchers also performed a standard examination of the entire specimen.
The study included a total of 407 consecutive patients (336 with colon and 71 rectum).
The researchers identified sentinel lymph nodes in 99.1% of colon and 91.5% of rectal patients.
In addition, the research team found skip metastases in 3.6% of colon vs. 2.8% of rectal patients.
Occult micrometastases were found in 13.4 % of colon vs. 7.0 % of rectal patients.
Except for success rates, no other parameters were statistically different between colon and rectum.
Dr Sahal commented, "Lower success in sentinel lymph node identification in rectal cancer may have been related to neoadjuvant chemoradiation received in all six of the patients with sentinel lymph node mapping failures."
"Despite higher success rates in sentinel lymph node identification for colon patients, sentinel lymph node mapping was highly successful (91.5 percent) in rectal patients."
Dr Sahal concluded, "Nodal upstaging, skip metastases, and occult metastases were similar."