Epithelial distribution of a myelomonocytic antigen L1 in relation to cutaneous malignancies and melanocytic naevi

summary The distribution of L1 antigen in four common skin tumours was examined immunohistochemically in 40 samples of formalin-fixed routine biopsy material. Presence of L1 in the dermis depended on the extent and composition of the inflammatory infiltrate; L1 was found mainly in reactive histiocytes and neutrophils. Intense epidermal staining was seen adjacent to squamous cell carcinoma, basal cell carcinoma and malignant melanoma, but not adjacent to melanocytic naevi. In specimens of melanocytic naevi, L1 staining around pilosebaceous units was weak or absent. Around the three malignant types of lesion, epidermal L1 positivity faded distally-thereby indicating the extent of the tumour. L1 was, in addition, expressed by the most highly differentiated cells in squamous cell carcinomas, whereas the other neoplasms were negative. Antibody to L1 may, thus, be a useful adjunct for distinction between various types of skin tumours.