Cellular blue nevus with nevus cells in a sentinel lymph node.

Regional lymph node involvement by a cellular blue nevus has been reported. However, it has recently been suggested that specific cases with "benign metastasizing" cellular blue nevi are actually rare. This study describes a typical case of a cellular blue nevus with nevus cells in a sentinel lymph node. We demonstrated that a cellular blue nevus clearly involved the regional lymph node and investigated the immunohistochemical profiles of such nodal cellular blue nevus cells. The location of the nevus cells fundamentally indicated a benign type, with limitation to the capsule and the fibrous trabeculae. However, only a few, isolated nevus cells were also seen in the parenchyma of the lymph node. The nevus cells in the capsule and the fibrous trabeculae were positive for c-kit, like the migrating melanocytes from the neural crest. In cellular blue nevi or lesions with similar histopathological features, it may be appropriate to consider the predominant involvement of the capsule as well as the benign cytological features and the immunohistochemical profiles (Ki-67-, PCNA-, and c-kit+) of the nodal cells to be a benign sign.

Merkel cell-poor trichoblastoma with basal cell carcinoma-like foci.

We reexamined 11 cases of trichoblastoma, and two cases of trichoblastoma with basal cell carcinoma (BCC)-like foci were found. In these two trichoblastomas with BCC-like foci, the BCC-like foci were often localized in peripheral or deep areas of lesions extending out of the fibrocytic stroma. Immunohistochemistry was performed in five conventional trichoblastomas and in two trichoblastomas with BCC-like foci, using antibodies against CK20 and CK15. No CK20-positive Merkel cells and no expression of CK15 were seen in any neoplastic aggregations of the two trichoblastomas with BCC-like foci. In contrast, increased numbers of Merkel cells and positive staining for CK15 were observed in all five trichoblastomas without BCC-like foci. The five trichoblastomas without BCC-like foci included two trichoblastomas with a popped out or shelled out appearance, which characteristically had a thick fibrous capsule surrounding the fibrotic stroma, demonstrating numerous Merkel cells in the aggregations. Some trichoblastomas may undergo mutations, resulting in the development of foci of BCC and in the loss of the expression of CK15 as well as the disappearance of Merkel cells.