Carbon dye staining of sentinel lymph nodes facilitates microstaging of colon cancer patients

Background: Carbon dye, when peritumourally injected, permanently marks the drainage site of sentinel lymph nodes (SLN). The objective of the current study was to evaluate whether the use of carbon dye facilitated the detection of small nodal tumour infiltrates in colon cancer patients. Methods: In a prospective trial, 19 patients underwent open, oncological resections of localized colon cancer and SLN procedure according to a standardized protocol. Isosulfan blue 1% and sterile filtered carbon dye (mixed 1:1) were injected into the subserosa circumferentially around the tumour. Lymph nodes staining blue were marked as SLN. Serial sections of each SLN were stained with hematoxylin and eosin (H&E) and with the pancytokeratin marker AE1/AE3. The intranodal presence and site of carbon particles were noted and compared with the location of possible tumour infiltrates. Results: Identification of at least one SLN was successful in 18 patients (identification rate 95%). Four patients (22%) were pN+, 11 (61%) were pN0(i-). Three patients (17%) were upstaged from pN0(i-) to pN0(i+) as isolated tumour cells were detected in their SLN: in two (11%) of the three patients, carbon dye and isolated tumour cells were found in the same nodal compartment, hence facilitating the recognition of isolated tumour cells by the pathologist. Conclusion: The use of carbon dye in the SLN procedure for colon cancer may facilitate the detection of small nodal tumour infiltrates.