Correct staging of patients with colorectal cancer: the significance of ex-vivo sentinel lymph node mapping in colorectal cancer

Background In recent years, the technique of sentinel lymph node mapping (SLNM) has been applied to colorectal cancer. One aim is to ultrastage those patients deemed to be node negative by routine pathological processing but who go on to develop systemic disease. Such a group may benefit from adjuvant chemotherapy.

Methods 40 patients with primary colorectal cancer were prospectively mapped with 1–2ml of isosulphan blue dye injected around tumors within 5–10 minutes of resection. During routine pathological analysis, all nodes were bi-valved and blue staining nodes were noted. These later underwent multi-level step sectioning with H+E and cytokeratin staining.

Results Sentinel lymph nodes (SLN) were found in 39 of 40 patients (98% sensitivity) with an average of 4.1 sentinel nodes per patient (range 1–8). Focussed examination of SLNs identified occult tumor deposits in 6 of 21 (29%) node negative patients. No metastatic cells were found in SLNs draining the 3 adenomas.

Conclusions The ability to identify SLNs after formalin fixation increases the ease and applicability of SLNM in colorectal cancer.