Purpose: Detection of micrometastasis in melanoma-draining lymph nodes is important for staging and prognosis. Immunohistochemical staining (IHC) using S-100p-HMB-45-, and MART-1 - specfic antibodies is used for detecting metastases in sentinel lymph nodes (SLN). However, improvement in IHC is needed for melanoma micrometastasis detection. Experimental Design: Paraffin-embedded archival tissue (PEAT) specimens were obtained from 42 non-SLN macrometastases, 42 SLN metastases, and 16 tumor-negative SLNs of 100 melanoma patients who underwent SLN biopsy. PEAT specimens were assessed by IHC with high molecular weight-melanoma-associated antigen (HMW-MAA)-specific monoclonal antibodies (mAb) and with S-100p-, HMB-45-, and MART-1 -specific antibodies. Quantitative real-time reverse-transcriptase PCR assay was used for HMW-MAA and MART-1 mRNA detection. Results: Expression frequency and immunostaining intensity were higher for HMW-MAA than MART-1 in nodal macrometastases (P < 0.0001 and P < 0.0001, respectively) and microme-tastases (P < 0.0001 and P = 0.004, respectively). All 52 (100%) macrometastases were positive with HMW-MAA-specific mAbs, whereas 43 (83%) were positive with MART-1 - specific mAbs. In a comparison analysis, 23 of 23 (100%) micrometastases were HMW-MAA - positive, whereas 21 (91%) and 18 (78%) specimens were S-100p- and HMB-45- positive, respectively. Quantitative real-time reverse-transcriptase PCR analysis of 48 nodal metastases showed HMW-MAA mRNA detection in SLNs with metastases. Conclusions: HMW-MAA is more sensitive and specific than MART-1, S-100p, and HMB-45 for IHC-based detection of SLN micrometastases. SLN PEAT-based detection specificity of melanoma micrometastases can be improved by IHC with HMW-MAA - specific mAbs.
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