Carbon dye histologically confirms the identity of sentinel lymph nodes in cutaneous melanoma

False-negative results from lymphatic mapping and sentinel lymphadenectomy (LM/SL) are associated with technical failures in nuclear medicine and surgery or with erroneous histologic evaluation. Any method that can confirm sentinel lymph node (SN) identity might decrease the false-negative rate. Carbon dye has been used as an adjunct to assist lymphadenectomy for some tumors, and the authors hypothesized that it could be used for the histologic verification of SNs removed during LM/SL. The current study assessed the clinical utility of carbon dye as a histopathologic adjunct for the identification of SNs in patients with melanoma and correlated the presence of carbon particles with the histopathologic status of the SNs.

LM/SL was performed using carbon dye (India ink) combined with isosulfan blue dye and sulfur colloid. Blue-stained and/or radioactive lymph nodes (two times background) were defined as SNs. Lymph nodes were evaluated for the presence of carbon particles and melanoma cells. If an SN lacked carbon dye in the initial histologic sections, four additional levels were obtained with S-100 protein and HMB-45 immunohistochemistry. Completion lymph node dissection (CLND) was performed if any SN contained melanoma cells.

One hundred patients underwent successful LM/SL in 120 lymph node regions. Carbon particles were identified in 199 SNs from 111 lymph node regions of 96 patients. Sixteen patients had tumor-positive SNs, all of which contained carbon particles. The anatomic location of the carbon particles within these tumor-positive SNs was found to be correlated with the location of tumor cells in the SNs. The presence of carbon particles appeared to be correlated with blue-black staining (P = 0.0001) and with tumor foci (P = 0.028). All 35 non-SNs that were removed during LM/SL were tumor-negative, and only 2 contained carbon particles. Of the 272 non-SNs removed during CLND, 5 contained metastases; 3 of these 5 were the only non-SNs that had carbon particles. The use of carbon particles during LM/SL was found to be safe and nontoxic.

Carbon dye used in LM/SL for melanoma permits the histologic confirmation of SNs. Carbon particles facilitate histologic evaluation by directing the pathologist to the SNs most likely to contain tumor. The location of carbon particles within SNs may assist the pathologist in the detection of metastases, thereby decreasing the histopathologic false-negative rate of LM/SL and subsequently reducing the same-basin recurrence rate.