Immunohistochemical stains fail to increase the detection rate of micrometastatic melanoma in completion regional lymph node dissection specimens

In melanoma patients, examination of tissue sections stained for immunohistochemical markers as an adjunct to examination of haematoxylin and eosin (H&E)-stained sections has been shown to increase the detection rate of micrometastatic disease in sentinel lymph nodes (SLNs). However, immunohistochemical stains are not routinely performed on completion regional lymph node dissection (CLND) specimens in most centres and it is not known whether their use would increase the detection of micrometastatic disease in these specimens. This study was performed to determine whether the application of immunohistochemical stains for S100 and HMB45 (in addition to H&E stains) increases the detection of micrometastatic disease in CLND specimens of melanoma patients and whether their use would be cost-effective in routine pathological practice. Forty-nine CLND specimens from patients with a prior positive SLN biopsy were examined by performing H&E stains and immunohistochemical stains for S100 protein and HMB-45 on each node, and the detection rate of melanoma metastases using H&E-stained sections was compared with that using immunohistochemically stained sections. The number of nodes in the CLND specimens ranged from 4 to 37 (median 14, mean 14.7). Nodal deposits of melanoma cells were detected in 12 of 49 cases (24%). Among these 12 positive cases, the mean number of positive nodes per CLND specimen was 2.2 (range, 1-14). The total number of positive nodes in the 12 CLND specimens was 27, accounting for 3.8% of the 720 nodes removed in the study group of 49 cases. Melanoma cells in all 27 positive nodes were identified both on the H&E-stained slides and the slides stained immunohistochemically for S100. The melanoma cells were positive for HMB45 in 24 of the 27 lymph nodes that contained metastatic melanoma (the metastatic melanoma cells were negative for HMB45 in three positive nodes from one specimen). No further positive lymph nodes were detected with the immunostains that had not been identified on the H&E-stained sections. This study suggests that the use of immunostains does not increase the detection rate of metastatic melanoma in CLND specimens, and that their routine use would not be cost-effective. We therefore recommend only H&E staining on sections of all lymph nodes in CLND specimens from melanoma patients.