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MART1 and MelanA are considered sensitive markers of melanocytic differentiation and are used to increase the detection of melanoma micrometastases in sentinel lymph nodes (SLNs). However, the false-positive rates of these two antibodies have not been adequately evaluated. We examined 217 lymph nodes (LNs) from patients with no history of melanoma: 117 SLNs from breast cancer patients, 79 LNs from other nonmelanoma malignancy patients, and 21 reactive LNs. Capsular melanocytic nevi were identified in 5 SLNs from 5 breast cancer patients by both antibodies. Two of these 5 SLNs with capsular nevus also contain MART1- and MelanA-positive cells within the lymph node parenchyma. Individual immunoperoxidase-positive cells were also identified within the parenchyma of lymph nodes without capsular nevus (9 LNs with MART1 and 3 LNs with MelanA). The false-positive rate is 5.1% for MART1 and 2.4% for MelanA. In conclusion, MART1- or MelanA-positive cells may be present in lymph nodes from patients without melanoma. Therefore, MART1- and MelanA-positive cells in SLNs from melanoma patients, without corresponding atypia or hematoxylin and eosin findings, should be interpreted with caution.
Yan et al. (Sat,) studied this question.